Management of the Colorado River: Water Allocations, Drought, and the Federal Role

Changes from May 23, 2023 to November 1, 2023

This page shows textual changes in the document between the two versions indicated in the dates above. Textual matter removed in the later version is indicated with ~~red strikethrough~~ and textual matter added in the later version is indicated with blue.

Management of the Colorado River: Water
May May 523, 2023 , 2023
Allocations, Drought, and the Federal Role
Charles V. Stern
The Colorado River Basin covers more than 246,000 square miles in seven U.S. states The Colorado River Basin covers more than 246,000 square miles in seven U.S. states
Specialist in Natural Specialist in Natural
(Wyoming, Colorado, Utah, New Mexico, Arizona, Nevada, and California) and Mexico. (Wyoming, Colorado, Utah, New Mexico, Arizona, Nevada, and California) and Mexico.
Resources Policy Resources Policy
Pursuant to federal law, the Bureau of Reclamation (part of the Department of the Interior) Pursuant to federal law, the Bureau of Reclamation (part of the Department of the Interior)

manages much of the basin’s water supplies. Colorado River water is used primarily for manages much of the basin’s water supplies. Colorado River water is used primarily for
Pervaze A. Sheikh
agricultural irrigation and municipal and industrial (M&I) uses; it is also important for agricultural irrigation and municipal and industrial (M&I) uses; it is also important for
Specialist in Natural Specialist in Natural
hydropower production, fish and wildlife, and recreational uses. hydropower production, fish and wildlife, and recreational uses.
Resources Policy Resources Policy

River Management
Kristen Hite
A collection of compacts, treaties, statutes, and other authorities govern Colorado River A collection of compacts, treaties, statutes, and other authorities govern Colorado River
Legislative Attorney Legislative Attorney
allocations and apportionments. The foundational management document, the Colorado River allocations and apportionments. The foundational management document, the Colorado River

Compact of 1922, established a framework to apportion water supplies between the river’s Upper Compact of 1922, established a framework to apportion water supplies between the river’s Upper
and Lower Basins, divided at Lee Ferry, AZ. The compact allocated 7.5 million acre-feet (MAF) and Lower Basins, divided at Lee Ferry, AZ. The compact allocated 7.5 million acre-feet (MAF)
For a copy of the full report, For a copy of the full report,
annually to each basin, and a 1994 treaty made an additional 1.5 MAF in annual flows available annually to each basin, and a 1994 treaty made an additional 1.5 MAF in annual flows available
please call 7-5700 or visit please call 7-5700 or visit
to Mexico. A Supreme Court case and related decrees inform the Secretary of the Interior’s to Mexico. A Supreme Court case and related decrees inform the Secretary of the Interior’s
www.crs.gov. www.crs.gov.
management of the delivery of all water below Hoover Dam. management of the delivery of all water below Hoover Dam.
Apportioned Colorado River water Apportioned Colorado River water ~~is in excess of~~exceeds the river’s natural flows, and actual consumptive use plus other water the river’s natural flows, and actual consumptive use plus other water
losses (e.g., evaporation) typically exceeds losses (e.g., evaporation) typically exceeds ~~natural~~ flows. This imbalanceflows. This imbalance ~~has stressed basin water supplies, exacerbated by a~~
, coupled with a long-term drought dating to 2000long-term drought dating to 2000~~. Reclamation and basin stakeholders closely track~~, has stressed basin water supplies. Reclamation closely tracks the status of two large reservoirs—Lake the status of two large reservoirs—Lake
Powell in the Upper Basin and Lake Mead in the Lower Basin—as indicators of basin storage conditions. Powell in the Upper Basin and Lake Mead in the Lower Basin—as indicators of basin storage conditions. ~~Under criteria~~
~~agreed upon by basin states, water releases from both lakes are tied to specific water storage levels.~~ Since the onset of Since the onset of
drought in the early 2000s, storage levels at these reservoirs have drought in the early 2000s, storage levels at these reservoirs have ~~been falling; in 2021 and 2022, Reclamation declared the~~
~~first-ever Tier One and Tier Two Shortages in the Lower Basin. These designations reduced water deliveries to contractors in~~
~~Arizona and Nevada, as well as~~fallen. To alleviate these trends, water releases from both lakes have been tied to specific water storage levels. Since 2020, pursuant to previous agreements, Reclamation has reduced water deliveries in Arizona and Nevada and reduced its deliveries to Mexico. In the Upper Basin, Lake Powell’s storage to Mexico. In the Upper Basin, Lake Powell’s storage ~~has also~~also has continued to drop continued to drop~~. This trend~~
~~could soon~~; some worry this could jeopardize hydropower generation at Glen Canyon Dam jeopardize hydropower generation at Glen Canyon Dam ~~and has led to operational changes in the Upper Basin.~~
. Wet conditions in 2023 improved the short-term outlook for both reservoirs. Efforts to Address Drought
The federal government has led multiple efforts to improve the basin’s water supply outlook, resulting in collaborative The federal government has led multiple efforts to improve the basin’s water supply outlook, resulting in collaborative
agreements in 2003 and 2007 and agreements in 2003 and 2007 and in the 2019 drought contingency plans (DCPs) for the Upper and Lower Colorado River the 2019 drought contingency plans (DCPs) for the Upper and Lower Colorado River
Basins. Basins. ~~The hydrologic outlook for the Colorado River Basin has deteriorated further since approval of the DCPs. Due~~In 2022, due to to
widespread concern about the basin’s long-term water supplies, Reclamation initiated a process to revise its near-term widespread concern about the basin’s long-term water supplies, Reclamation initiated a process to revise its near-term
operational guidelines for river management. In April 2023, the bureau published a draft environmental impact statement operational guidelines for river management. In April 2023, the bureau published a draft environmental impact statement
with with ~~two~~ action alternatives that action alternatives that ~~both~~ would have imposed additional water delivery cutbacks on Lower Basin would have imposed additional water delivery cutbacks on Lower Basin contractors~~contractors in~~
~~2024-2026 but differed in how they allocated water cuts~~. On May 22, 2023, the Department of the Interior . On May 22, 2023, the Department of the Interior and basin states announced a announced a
consensus-based proposal in which the three Lower Basin states will conserve a total of 3 MAF prior to 2026, with 2.3 MAF consensus-based proposal in which the three Lower Basin states will conserve a total of 3 MAF prior to 2026, with 2.3 MAF
of these cuts compensated by the federal government of these cuts compensated by the federal government ~~via~~using previously appropriated funds. Reclamation is analyzing this proposal in the context of improved 2023 hydrology and expects to finalize a near-term plan by the end of 2023. Parallel to this process, Reclamation is analyzing options for long-term (post-2026) basin operations ~~previously appropriated funds. The initial announcement did not~~
~~specify allocations of curtailments at the state or contractor level, or how these cuts would be tied to specific Lake Mead~~
~~elevations~~. .
Congressional Role
Congress funds and oversees management of basin water and power facilities. Congress has enacted legislation affecting Congress funds and oversees management of basin water and power facilities. Congress has enacted legislation affecting
Colorado River waters (e.g., Indian water rights settlementsColorado River waters (e.g., Indian water rights settlements;, new water storage facilities) and authorizing water shortage new water storage facilities) and authorizing water shortage
mitigation (e.g., the DCPs and other related efforts). Section 50233 of P.L. 117-169 (popularly known as the Inflation mitigation (e.g., the DCPs and other related efforts). Section 50233 of P.L. 117-169 (popularly known as the Inflation
Reduction Act) provided $4.0 billion for drought mitigation in the West, and this funding will compensate water contractors Reduction Act) provided $4.0 billion for drought mitigation in the West, and this funding will compensate water contractors
for recently agreed-upon delivery reductions. for recently agreed-upon delivery reductions. Most of the recent efforts to improve the basin’s water supply outlook expire in 2026. Congress may consider further amending existing authorities or funding Congress may consider further amending existing authorities or funding
mitigation activities for basin water shortages. mitigation activities for basin water shortages.
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Introduction
From its headwaters in Colorado and Wyoming to its terminus in the Gulf of California, the Colorado From its headwaters in Colorado and Wyoming to its terminus in the Gulf of California, the Colorado
River Basin covers more than 246,000 square miles. The basin spans seven U.S. states (Wyoming, River Basin covers more than 246,000 square miles. The basin spans seven U.S. states (Wyoming,
Colorado, Utah, New Mexico, Arizona, Nevada, and California) and two countries (the United States and Colorado, Utah, New Mexico, Arizona, Nevada, and California) and two countries (the United States and
Mexico). Pursuant to federal law, the Bureau of Reclamation (Reclamation), a component of the Mexico). Pursuant to federal law, the Bureau of Reclamation (Reclamation), a component of the
Department of the Interior (DOI), plays a prominent role in the management of the basin’s waters. In the Department of the Interior (DOI), plays a prominent role in the management of the basin’s waters. In the
Lower Basin (i.e., Arizona, Nevada, and California), Reclamation also serves as Lower Basin (i.e., Arizona, Nevada, and California), Reclamation also serves as water master on behalf on behalf
of the Secretary of the Interior, a role that elevates the status of the federal government in basin water of the Secretary of the Interior, a role that elevates the status of the federal government in basin water
management.1 The federal role in managing Colorado River water is magnified by the multiple federally management.1 The federal role in managing Colorado River water is magnified by the multiple federally
owned and operated water storage and conveyance facilities in the basin, which provide low-cost water owned and operated water storage and conveyance facilities in the basin, which provide low-cost water
and hydropower supplies. and hydropower supplies.
Colorado River water is used primarily for agricultural irrigation and municipal and industrial (M&I) Colorado River water is used primarily for agricultural irrigation and municipal and industrial (M&I)
purposes. The river’s flow and stored water also are important for power production, fish and wildlife, purposes. The river’s flow and stored water also are important for power production, fish and wildlife,
and recreation, among other uses. A majority of basin water supplies (70%) are used to irrigate 5.5 million and recreation, among other uses. A majority of basin water supplies (70%) are used to irrigate 5.5 million
acres of land; basin waters also provide M&I water supplies to nearly 40 million people.2 Much of the acres of land; basin waters also provide M&I water supplies to nearly 40 million people.2 Much of the
area that depends on the river for its water supplies is outside of the drainage area area that depends on the river for its water supplies is outside of the drainage area ~~for~~of the Colorado River the Colorado River
Basin. Storage and conveyance facilities on the Colorado River provide trans-basin diversions that serve Basin. Storage and conveyance facilities on the Colorado River provide trans-basin diversions that serve
areas such as Cheyenne, WY; multiple cities in Colorado’s Front Range (e.g., Fort Collins, Denver, areas such as Cheyenne, WY; multiple cities in Colorado’s Front Range (e.g., Fort Collins, Denver,
Boulder, and Colorado Springs, CO); Provo, UT; Albuquerque and Santa Fe, NM; and Los Angeles, San Boulder, and Colorado Springs, CO); Provo, UT; Albuquerque and Santa Fe, NM; and Los Angeles, San
Diego, and the Imperial Valley in Southern Diego, and the Imperial Valley in Southern ~~California~~ California (Figure 1). . Colorado River hydropower facilities Colorado River hydropower facilities
can provide up to 4,200 megawatts of electrical power per year.3 The river also provides habitat for a wide can provide up to 4,200 megawatts of electrical power per year.3 The river also provides habitat for a wide
range of species, including several species listed under the federal Endangered Species Act (ESA; 87 Stat. range of species, including several species listed under the federal Endangered Species Act (ESA; 87 Stat.
884, 16 U.S.C. §§1531-1544). It flows through seven national wildlife refuges and 11 National Park 884, 16 U.S.C. §§1531-1544). It flows through seven national wildlife refuges and 11 National Park
Service (NPS) units; these and other areas of the river support important recreational opportunities.4 Service (NPS) units; these and other areas of the river support important recreational opportunities.4

1 As discussed later in 1 As discussed later in “The Law of the River: Foundational Documents and Programs,” the Boulder Canyon Project Act of 1928 the Boulder Canyon Project Act of 1928
made the Secretary of the Interior responsible for the distribution (via contract) of all Colorado River water delivered below made the Secretary of the Interior responsible for the distribution (via contract) of all Colorado River water delivered below
Hoover Dam (i.e., the Lower Basin), and authorized such regulations as necessary to enter into these contracts. Subsequent court Hoover Dam (i.e., the Lower Basin), and authorized such regulations as necessary to enter into these contracts. Subsequent court
decisions confirmed the Secretary’s power to apportion surpluses and shortages among and within Lower Basin states; this forms decisions confirmed the Secretary’s power to apportion surpluses and shortages among and within Lower Basin states; this forms
the basis for the designation Lower Basin the basis for the designation Lower Basin water master. No similar authorities or designations have been provided for the Upper . No similar authorities or designations have been provided for the Upper
Basin. Basin.
2 U.S. Bureau of Reclamation (Reclamation), 2 U.S. Bureau of Reclamation (Reclamation), Colorado River Basin Water Supply and Demand Study, p. 4, December 2012, at , p. 4, December 2012, at
https://www.usbr.gov/lc/region/programs/crbstudy/finalreport/index.html. https://www.usbr.gov/lc/region/programs/crbstudy/finalreport/index.html.
3 Ibid., p. 3. 3 Ibid., p. 3.
4 Ibid. 4 Ibid.
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Management of the Colorado River: Water Allocations, Drought, and the Federal Role

Figure 1. Colorado River Basin and U.S. Areas That Import Colorado River Water

Source: Bureau of Reclamation, Bureau of Reclamation, Colorado River Basin Water Supply and Demand Study, 2012. , 2012.
Precipitation and runoff in the basin are highly variable. Water conditions on the river depend largely on Precipitation and runoff in the basin are highly variable. Water conditions on the river depend largely on
snowmelt in the basin’s northern areas. From 1906 to snowmelt in the basin’s northern areas. From 1906 to ~~2022~~2023, natural flows in the Colorado River Basin , natural flows in the Colorado River Basin
averaged about 14.6 million acre-feet (MAF) annually.5 Flows have dipped significantly averaged about 14.6 million acre-feet (MAF) annually.5 Flows have dipped significantly ~~during the~~

~~5 Reclamation, “PROVISIONAL Natural Flow Data~~since 2000; 5 CRS analysis of Bureau of Reclamation, “Provisional Natural Flow Data, 1906-2023 (Excel file, 0.3 MB) based on the April, 2023 24 MS,” at 1906-2023 (Excel file, 0.3 MB) based on the April, 2023 24 MS,” at
https://www.usbr.gov/lc/region/g4000/NaturalFlow/LFnatFlow1906-2023.2023.4.17.xlsx. Hereinafter, Reclamation, https://www.usbr.gov/lc/region/g4000/NaturalFlow/LFnatFlow1906-2023.2023.4.17.xlsx. Hereinafter, Reclamation,
“Reclamation Flow Data.” “Reclamation Flow Data.”
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Management of the Colorado River: Water Allocations, Drought, and the Federal Role

~~current drought, which dates to 2000;~~ annual natural flows from 2000 to annual natural flows from 2000 to ~~2022~~2023 averaged approximately averaged approximately
12.12.15 MAF per year.6 MAF per year.6 ~~Reclamation has noted that~~According to Reclamation, the 23-year period from 2000 to 2022 was the driest 23- the 23-year period from 2000 to 2022 was the driest 23-
year period in more than 100 years year period in more than 100 years of Colorado River of record keeping, and among the driest periods in the past 1,200 record keeping, and among the driest periods in the past 1,200
years.7 Climate change impacts, including warmer temperatures and altered precipitation patterns, may years.7 Climate change impacts, including warmer temperatures and altered precipitation patterns, may
further increase the likelihood of prolonged drought in the basin.8 further increase the likelihood of prolonged drought in the basin.8
Congress plays a prominent role in the management of the Colorado River. Congress plays a prominent role in the management of the Colorado River. ~~Specifically,~~ Congress funds Congress funds
and oversees Reclamation’s management of Colorado River Basin facilities, including facility operations and oversees Reclamation’s management of Colorado River Basin facilities, including facility operations
and programs to protect and restore endangered and threatened species. Congress has also approved and and programs to protect and restore endangered and threatened species. Congress has also approved and
continues to consider Indian water rights settlements involving Colorado River waters, and development continues to consider Indian water rights settlements involving Colorado River waters, and development
of new and expanded water storage in the basin. In addition, Congress has approved supplemental of new and expanded water storage in the basin. In addition, Congress has approved supplemental
funding to mitigate drought and stretch basin water supplies, and new authorities for Reclamation to funding to mitigate drought and stretch basin water supplies, and new authorities for Reclamation to
combat drought and enter into agreements with states and combat drought and enter into agreements with states and those who are contracted to receive water from federal Colorado Colorado River infrastructure (i.e., contractors)~~River contractors~~. This report . This report
provides background on management of the Colorado River, with a focus on recent developments. It also provides background on management of the Colorado River, with a focus on recent developments. It also
discusses the congressional role in the management of basin waters. discusses the congressional role in the management of basin waters.
The Law of the River:
Foundational Documents and Programs
The The Law of the River refers to a collection of compacts, treaties, statutes, and other authorities that govern refers to a collection of compacts, treaties, statutes, and other authorities that govern
Colorado River allocations and apportionments.9 In the latter part of the 19th century, interested parties in Colorado River allocations and apportionments.9 In the latter part of the 19th century, interested parties in
the Colorado River Basin began to recognize that local interests alone could not solve the challenges the Colorado River Basin began to recognize that local interests alone could not solve the challenges
associated with development of the Colorado River. Plans conceived by parties in California’s Imperial associated with development of the Colorado River. Plans conceived by parties in California’s Imperial
Valley to divert water from the mainstream of the Colorado River were thwarted because these proposals Valley to divert water from the mainstream of the Colorado River were thwarted because these proposals
were subject to the sovereignty of both the United States and Mexico.10 The river also presented were subject to the sovereignty of both the United States and Mexico.10 The river also presented
engineering challenges, such as deep canyons and erratic water flows, and economic hurdles that engineering challenges, such as deep canyons and erratic water flows, and economic hurdles that
prevented local or state groups from building the necessary storage facilities and canals to provide an prevented local or state groups from building the necessary storage facilities and canals to provide an
adequate water supply. In part because local or state groups could not resolve these “national problems,” adequate water supply. In part because local or state groups could not resolve these “national problems,”
Congress considered options to control the Colorado River and resolve potential conflicts between the Congress considered options to control the Colorado River and resolve potential conflicts between the
states.11 In an effort to resolve these conflicts and avoid litigation, Congress gave its consent for the states states.11 In an effort to resolve these conflicts and avoid litigation, Congress gave its consent for the states
and Reclamation to enter into an agreement to apportion Colorado River water supplies in 1921.12 and Reclamation to enter into an agreement to apportion Colorado River water supplies in 1921.12

6 6 ~~Ibid~~CRS Analysis of Reclamation Flow Data. .
7 Reclamation, Department of the Interior, “Request for Input on Development of Post-2026 Colorado River Reservoir 7 Reclamation, Department of the Interior, “Request for Input on Development of Post-2026 Colorado River Reservoir
Operational Strategies for Lake Powell and Lake Mead Under Historically Low Reservoir Conditions,” 87Operational Strategies for Lake Powell and Lake Mead Under Historically Low Reservoir Conditions,” 87 Federal Register
37884, June 24, 2022. Hereinafter 87 FR 37884, 2022. For additional discussion on historic drought in the Colorado River, see 37884, June 24, 2022. Hereinafter 87 FR 37884, 2022. For additional discussion on historic drought in the Colorado River, see
Subhrendu Gangopadhyay, Connie A. Woodhouse, and Gregory J. McCabe, “Tree Rings Reveal Unmatched 2nd Century Subhrendu Gangopadhyay, Connie A. Woodhouse, and Gregory J. McCabe, “Tree Rings Reveal Unmatched 2nd Century
Drought in the Colorado River Basin,” Drought in the Colorado River Basin,” Geophysical Research Letters, vol. 49, no. 11 (June 2022). , vol. 49, no. 11 (June 2022).
8 B. Udall and J. Overpeck, “The Twenty-First Century Colorado River Hot Drought and Implications for the Future,” 8 B. Udall and J. Overpeck, “The Twenty-First Century Colorado River Hot Drought and Implications for the Future,” Water
Resources Research, vol. 53 (February 17, 2017), pp. 2404-2418. , vol. 53 (February 17, 2017), pp. 2404-2418.
9 For an example of how courts characterize the Law of the River, see, for example, Navajo Nation v. Dep’t of the Interior, 26 9 For an example of how courts characterize the Law of the River, see, for example, Navajo Nation v. Dep’t of the Interior, 26
F.4th 794, 800 (9th Cir. 2022). F.4th 794, 800 (9th Cir. 2022).
10 Arizona v. California, 373 U.S. 546 (1963). Hereinafter, Arizona v. California. 10 Arizona v. California, 373 U.S. 546 (1963). Hereinafter, Arizona v. California.
11 S. Doc. No. 67-142 (1922). For example, the states in the Upper Basin (Colorado, Wyoming, Utah, and New Mexico), where 11 S. Doc. No. 67-142 (1922). For example, the states in the Upper Basin (Colorado, Wyoming, Utah, and New Mexico), where
the majority of the river’s runoff originates, feared that a storage facility making water available downstream might form a basis the majority of the river’s runoff originates, feared that a storage facility making water available downstream might form a basis
for claims to priority access to basin waters by Lower Basin states before Upper Basin states could develop means to access their for claims to priority access to basin waters by Lower Basin states before Upper Basin states could develop means to access their
share. share.
12 Ch. 72, 42 Stat. 171 (1921). In lieu of litigation, interstate compacts have historically been a preferred means of allocating 12 Ch. 72, 42 Stat. 171 (1921). In lieu of litigation, interstate compacts have historically been a preferred means of allocating
~~water among competing uses. Pursuant to the U.S. Constitution, Article I, Section 10, Clause 3, no such compacts can be entered~~
~~into without the consent of Congress.~~
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The below sections discuss the resulting agreement, the Colorado River Compact, as well as key statutory The below sections discuss the resulting agreement, the Colorado River Compact, as well as key statutory
authorities, the Supreme Court’s decision in authorities, the Supreme Court’s decision in Arizona v. California, and other documents and agreements , and other documents and agreements
that form the basis of the Law of the River. that form the basis of the Law of the River.
Colorado River Compact
The Colorado River Compact of 1922, negotiated by the seven basin states and the federal government, The Colorado River Compact of 1922, negotiated by the seven basin states and the federal government,
was initially signed by all but one basin state (Arizona).13 Under the compact, the states established a was initially signed by all but one basin state (Arizona).13 Under the compact, the states established a
framework to apportion the water supplies between the Upper Basin and the Lower Basin, with the framework to apportion the water supplies between the Upper Basin and the Lower Basin, with the
dividing line between the two basins located at Lee Ferry, AZ,14 below the confluence of the Colorado and dividing line between the two basins located at Lee Ferry, AZ,14 below the confluence of the Colorado and
Paria Rivers near the Utah border.15 Each basin was apportioned 7.5 MAF annually for beneficial Paria Rivers near the Utah border.15 Each basin was apportioned 7.5 MAF annually for beneficial
consumptive use, and the Lower Basin was given the right to increase its beneficial consumptive use by consumptive use, and the Lower Basin was given the right to increase its beneficial consumptive use by
an additional 1 MAF annually. The agreement also required that Upper Basin states not deplete more than an additional 1 MAF annually. The agreement also required that Upper Basin states not deplete more than
a total of 75 MAF over any 10-year period (i.e., 7.5 MAF per year), thus allowing for averaging over time a total of 75 MAF over any 10-year period (i.e., 7.5 MAF per year), thus allowing for averaging over time
to make up for low-flow years. The compact did not address inter- or intrastate allocations of water to make up for low-flow years. The compact did not address inter- or intrastate allocations of water
(which it left to future agreements and legislation), nor did it address tribal rights or other rights that (which it left to future agreements and legislation), nor did it address tribal rights or other rights that
existed at the time the compact was finalized.16 The compact also contemplated how the basins could existed at the time the compact was finalized.16 The compact also contemplated how the basins could
share the burden of provisioning water to Mexico, the river’s natural terminus, the details of which were share the burden of provisioning water to Mexico, the river’s natural terminus, the details of which were
addressed in subsequent international agreements.17 The compact was not to become binding until it had addressed in subsequent international agreements.17 The compact was not to become binding until it had
been approved by the legislatures of each of the signatory states and by Congress. been approved by the legislatures of each of the signatory states and by Congress.
Boulder Canyon Project Act
Congress approved and modified the Colorado River Compact in the Boulder Canyon Project Act (BCPA) Congress approved and modified the Colorado River Compact in the Boulder Canyon Project Act (BCPA)
of 1928.18 The BCPA ratified the 1922 compact, and authorized the construction of a federal facility to of 1928.18 The BCPA ratified the 1922 compact, and authorized the construction of a federal facility to
impound water in the Lower Basin (Boulder Dam, later renamed Hoover Dam) and of related facilities to impound water in the Lower Basin (Boulder Dam, later renamed Hoover Dam) and of related facilities to
deliver water in Southern California (e.g., the All-American Canal, which delivers Colorado River water deliver water in Southern California (e.g., the All-American Canal, which delivers Colorado River water
to California’s Imperial Valley). The BCPA apportioned the Lower Basin’s 7.5 MAF per year among the to California’s Imperial Valley). The BCPA apportioned the Lower Basin’s 7.5 MAF per year among the
three Lower Basin states: 4.4 MAF per year to California, 2.8 MAF to Arizona, and 300,000 acre-feet three Lower Basin states: 4.4 MAF per year to California, 2.8 MAF to Arizona, and 300,000 acre-feet
(AF) to Nevada, with the states to divide any surplus waters among them. It also directed the Secretary of (AF) to Nevada, with the states to divide any surplus waters among them. It also directed the Secretary of
the Interior to serve as the sole contracting authority for Colorado River water use in the Lower Basin and the Interior to serve as the sole contracting authority for Colorado River water use in the Lower Basin and
authorized several storage projects for study in the Upper Basin. authorized several storage projects for study in the Upper Basin.
Congress’s approval of the compact in the BCPA was conditioned on a number of factors, including Congress’s approval of the compact in the BCPA was conditioned on a number of factors, including
ratification of the compact by California and five other states (thereby allowing the compact to become ratification of the compact by California and five other states (thereby allowing the compact to become
effective without Arizona’s concurrence), and California agreeing by act of its legislature to limit its water effective without Arizona’s concurrence), and California agreeing by act of its legislature to limit its water

water among competing uses. Pursuant to the U.S. Constitution, Article I, Section 10, Clause 3, no such compacts can be entered into without the consent of Congress. 13 Because the Colorado River Compact of 1922 did not specify the apportionments for individual states, Arizona initially refused 13 Because the Colorado River Compact of 1922 did not specify the apportionments for individual states, Arizona initially refused
to sign and ratify the agreement out of concern that rapidly growing California would lay claim to most of the Lower Basin’s to sign and ratify the agreement out of concern that rapidly growing California would lay claim to most of the Lower Basin’s
share of water. Arizona signed and ratified the compact in 1944. share of water. Arizona signed and ratified the compact in 1944.
14 14 Lee Ferry is the dividing line between basins designated in the compact. is the dividing line between basins designated in the compact. Lees Ferry (or (or Lee’s Ferry), approximately 1 mile ), approximately 1 mile
upstream from that point, is the location of the USGS streamgage that has measured flows dating to 1921. After the compact was upstream from that point, is the location of the USGS streamgage that has measured flows dating to 1921. After the compact was
signed, the Lees Ferry streamgage, along with a gage on the Paria River, became the measurements used to determine compliance signed, the Lees Ferry streamgage, along with a gage on the Paria River, became the measurements used to determine compliance
with the compact. with the compact.
15 Arizona receives water under both the Upper and the Lower Basin apportionments, because parts of the state are in both basins. 15 Arizona receives water under both the Upper and the Lower Basin apportionments, because parts of the state are in both basins.
16 Boulder Canyon Project Act (BCPA), 45 Stat. 64–65, as codified in 43 U.S.C. §§617l–q; 16 Boulder Canyon Project Act (BCPA), 45 Stat. 64–65, as codified in 43 U.S.C. §§617l–q; c.f. Boulder Canyon Project Boulder Canyon Project
Adjustment Act, 54 Stat. 799, as codified in 43 U.S.C. §618m (containing similar savings clause language). Adjustment Act, 54 Stat. 799, as codified in 43 U.S.C. §618m (containing similar savings clause language).
17 Colorado River Compact Art. III(c). See below 17 Colorado River Compact Art. III(c). See below ~~section,~~ section, “1944 U.S.-Mexico Water Treaty.”
18 BCPA, Ch. 42, 45 Stat. 1057 (1928), codified as amended at 43 U.S.C. §617. 18 BCPA, Ch. 42, 45 Stat. 1057 (1928), codified as amended at 43 U.S.C. §617.
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use to 4.4 MAF per year and not more than half of any surplus waters. California met this requirement by use to 4.4 MAF per year and not more than half of any surplus waters. California met this requirement by
passing the California Limitation Act of March 4, 1929, and the compact became effective on that date.19 passing the California Limitation Act of March 4, 1929, and the compact became effective on that date.19
1944 U.S.-Mexico Water Treaty20
In 1944, the United States signed a water treaty with Mexico (1944 U.S.-Mexico Water Treaty) to guide In 1944, the United States signed a water treaty with Mexico (1944 U.S.-Mexico Water Treaty) to guide
how the two countries share the waters of the Colorado River.21 The treaty established water allocations how the two countries share the waters of the Colorado River.21 The treaty established water allocations
for the two countries and created a governance framework (i.e., the International Boundary and Water for the two countries and created a governance framework (i.e., the International Boundary and Water
Commission) to resolve disputes arising from the treaty’s execution. The treaty requires the United States Commission) to resolve disputes arising from the treaty’s execution. The treaty requires the United States
to provide Mexico with 1.5 MAF of Colorado River water annually, plus an additional 200,000 AF when to provide Mexico with 1.5 MAF of Colorado River water annually, plus an additional 200,000 AF when
a surplus is declared. During drought, the United States may reduce deliveries to Mexico in similar a surplus is declared. During drought, the United States may reduce deliveries to Mexico in similar
proportion to reductions of U.S. consumptive uses. The treaty has been supplemented by additional proportion to reductions of U.S. consumptive uses. The treaty has been supplemented by additional
agreements between the United States and Mexico, known as agreements between the United States and Mexico, known as minutes, regarding matters related to the , regarding matters related to the
treaty’s execution and interpretation.22 treaty’s execution and interpretation.22
Arizona v. California
Arizona ratified the Colorado River Compact in 1944, at which time the state began to pursue a federal Arizona ratified the Colorado River Compact in 1944, at which time the state began to pursue a federal
project (later named the Central Arizona Project, or CAP) to bring Colorado River water to its primary project (later named the Central Arizona Project, or CAP) to bring Colorado River water to its primary
population centers in Phoenix and Tucson. California opposed the project, claiming it had senior water population centers in Phoenix and Tucson. California opposed the project, claiming it had senior water
rights based on its “first in time” use under the doctrine of prior appropriation and that any diversions rights based on its “first in time” use under the doctrine of prior appropriation and that any diversions
from Colorado River from Colorado River tributaries should be included in Arizona’s allotted 2.8 MAF under the Colorado should be included in Arizona’s allotted 2.8 MAF under the Colorado
River Compact.23 In 1952, Arizona filed suit against California in the U.S. Supreme Court to settle these River Compact.23 In 1952, Arizona filed suit against California in the U.S. Supreme Court to settle these
and other issues.24 and other issues.24
Eleven years later, in the 1963 Eleven years later, in the 1963 Arizona v. California decision, the Supreme Court ruled in favor of decision, the Supreme Court ruled in favor of
Arizona.25 The ruling was notable in forgoing typical Reclamation deference to state law under the Arizona.25 The ruling was notable in forgoing typical Reclamation deference to state law under the
Reclamation Act of 1902 and formed the basis for the Secretary of the Interior’s role as Reclamation Act of 1902 and formed the basis for the Secretary of the Interior’s role as water master for for

19 The Department of the Interior also requested that California prioritize its Colorado River rights among users before the 19 The Department of the Interior also requested that California prioritize its Colorado River rights among users before the
Colorado River Compact became effective; the state established priority among these users for water in both “normal” and Colorado River Compact became effective; the state established priority among these users for water in both “normal” and
“surplus” years in the California Seven-Party Agreement, signed in August 1931. “surplus” years in the California Seven-Party Agreement, signed in August 1931.
20 For more information on the 1994 U.S.-Mexico Water Treaty and Colorado River water sharing issues with Mexico, see CRS 20 For more information on the 1994 U.S.-Mexico Water Treaty and Colorado River water sharing issues with Mexico, see CRS
Report R42917, Report R42917, Mexico: Background and U.S. Relations, by Clare Ribando Seelke and Joshua Klein. , by Clare Ribando Seelke and Joshua Klein.
21 The treaty also included water-sharing provisions relating to the Lower Rio Grande and Tijuana Rivers. See Treaty Between 21 The treaty also included water-sharing provisions relating to the Lower Rio Grande and Tijuana Rivers. See Treaty Between
the United States of America and Mexico Respecting Utilization of Waters of the Colorado and Tijuana Rivers and of the Rio the United States of America and Mexico Respecting Utilization of Waters of the Colorado and Tijuana Rivers and of the Rio
Grande, U.S.-Mex., February 3, 1944, 59 State. 1219, at https://www.ibwc.gov/Treaties_Minutes/treaties.html. Mexico ratified it Grande, U.S.-Mex., February 3, 1944, 59 State. 1219, at https://www.ibwc.gov/Treaties_Minutes/treaties.html. Mexico ratified it
on October 16, 1945 and the United States ratified the treaty on November 1, 1945. It became effective on November 8, 1945. on October 16, 1945 and the United States ratified the treaty on November 1, 1945. It became effective on November 8, 1945.
22 International Boundary 22 International Boundary &and Water Commission, Minutes between the United States and Mexican Sections of the IBWC, Water Commission, Minutes between the United States and Mexican Sections of the IBWC,
at https://www.ibwc.gov/Treaties_Minutes/Minutes.html. For more information on recent minutes, see section, https://www.ibwc.gov/Treaties_Minutes/Minutes.html. For more information on recent minutes, see section, “Minute 319 and
Minute 323 Agreements with Mexico.”
23 Historically, water in the western United States (versus riparian rights in the eastern portion) has been governed by some form 23 Historically, water in the western United States (versus riparian rights in the eastern portion) has been governed by some form
of the of the rule of prior appropriation. Under this rule, the party that first appropriates water and puts it to . Under this rule, the party that first appropriates water and puts it to beneficial use thereby thereby
acquires a vested right to continue to divert and use that quantity of water against claimants junior in time. acquires a vested right to continue to divert and use that quantity of water against claimants junior in time.
24 Article III of the Constitution states that in all cases in which a state shall be a party, the Supreme Court has original 24 Article III of the Constitution states that in all cases in which a state shall be a party, the Supreme Court has original
jurisdiction. U.S. Constitution, Article III, §2, cl. 2. In original jurisdiction cases, the Supreme Court issues detailed decrees that jurisdiction. U.S. Constitution, Article III, §2, cl. 2. In original jurisdiction cases, the Supreme Court issues detailed decrees that
are more akin to trial court judgments than the Supreme Court’s usual appellate decisions. are more akin to trial court judgments than the Supreme Court’s usual appellate decisions.
25 The 1963 Supreme Court decision in Arizona v. California25 The 1963 Supreme Court decision in Arizona v. California is the first in a line of Supreme Court decisions and orders in the is the first in a line of Supreme Court decisions and orders in the
same litigation that address water allocation disputes within the Lower Basin. 373 U.S. 546, 601 (1963), 376 U.S. 340 (1964) same litigation that address water allocation disputes within the Lower Basin. 373 U.S. 546, 601 (1963), 376 U.S. 340 (1964)
(order issued), 383 U.S. 268 (1966) (amending judgment), 466 U.S. 144 (1984) (amending order), 530 U.S. 392 (2000) (order issued), 383 U.S. 268 (1966) (amending judgment), 466 U.S. 144 (1984) (amending order), 530 U.S. 392 (2000)
(subsequent determination), 531 U.S. 1 (2000) (supplemented), 547 U.S. 150 (2006) (consolidated decree); (subsequent determination), 531 U.S. 1 (2000) (supplemented), 547 U.S. 150 (2006) (consolidated decree); cf. California v.
United States, 438 U.S. 645 (1978). , 438 U.S. 645 (1978).
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the Lower Basin.26 The Court determined that the BCPA serves as the framework for apportioning the the Lower Basin.26 The Court determined that the BCPA serves as the framework for apportioning the
Lower Basin’s share of the mainstream waters of the Colorado River, neither the BCPA nor water Lower Basin’s share of the mainstream waters of the Colorado River, neither the BCPA nor water
contracts require any specific formula for apportioning shortages, and the Secretary of the Interior contracts require any specific formula for apportioning shortages, and the Secretary of the Interior
exercises considerable control in managing the delivery of water from Lake Mead to the Lower Basin. exercises considerable control in managing the delivery of water from Lake Mead to the Lower Basin.
The Court determined that the Colorado River Compact guides resolution of disputes regarding The Court determined that the Colorado River Compact guides resolution of disputes regarding
allocations between basins, that statutory authority—in this case the BCPA—guides Lower Basin water allocations between basins, that statutory authority—in this case the BCPA—guides Lower Basin water
allocations originating from the main stream of the River, and that tributary allocations are reserved to the allocations originating from the main stream of the River, and that tributary allocations are reserved to the
states.27 Although California argued its historical use of the river trumped Arizona’s rights to the Arizona states.27 Although California argued its historical use of the river trumped Arizona’s rights to the Arizona
allotment, the Court rejected this argument because Congress had spoken definitively to the contrary.28 allotment, the Court rejected this argument because Congress had spoken definitively to the contrary.28
A key element of the suit concerned the extent to which Arizona’s Gila River diversions should count A key element of the suit concerned the extent to which Arizona’s Gila River diversions should count
toward its allocation in the Colorado River Compact and BCPA. The Supreme Courttoward its allocation in the Colorado River Compact and BCPA. The Supreme Court concluded that the concluded that the
BCPA and compact’s 7.5 MAF allocations within and between basins apply only to the mainstream of the BCPA and compact’s 7.5 MAF allocations within and between basins apply only to the mainstream of the
Colorado River. 29 Tributary allocations, such as from Arizona’s diversion of water from the Gila River, Colorado River. 29 Tributary allocations, such as from Arizona’s diversion of water from the Gila River,
are governed under separate authorities.30 are governed under separate authorities.30
As detailed in the Supreme Court’s opinion, Congress granted DOI the exclusive authority to enter into As detailed in the Supreme Court’s opinion, Congress granted DOI the exclusive authority to enter into
contracts with Lower Basin users to apportion stored water pursuant to BCPA Section 5.31 The resulting contracts with Lower Basin users to apportion stored water pursuant to BCPA Section 5.31 The resulting
contracts determine how mainstream water is delivered to Lower Basin users. In the event of shortages, contracts determine how mainstream water is delivered to Lower Basin users. In the event of shortages,
the Secretary of the Interior has discretion to determine how to divide the burden of shortages in the the Secretary of the Interior has discretion to determine how to divide the burden of shortages in the
Lower Basin among the three states, within the parameters of the BCPA and water contracts.32 The Court Lower Basin among the three states, within the parameters of the BCPA and water contracts.32 The Court
clarified that DOI is not bound by a single approach to addressing shortages and acknowledged that one clarified that DOI is not bound by a single approach to addressing shortages and acknowledged that one
valid option could be to reduce lower basin deliveries proportionally to statutory allocations of the first valid option could be to reduce lower basin deliveries proportionally to statutory allocations of the first
7.5 MAF (California 4.4/7.5, Arizona 2.8/7.5, and Nevada 0.3/7.5). DOI also has the authority and 7.5 MAF (California 4.4/7.5, Arizona 2.8/7.5, and Nevada 0.3/7.5). DOI also has the authority and
discretion to elect an alternate basis for apportioning shortages, subject to statutory constraints.33 These discretion to elect an alternate basis for apportioning shortages, subject to statutory constraints.33 These
constraints include the congressionally directed priorities for uses of the dam and reservoir, as well as constraints include the congressionally directed priorities for uses of the dam and reservoir, as well as
limitations reflected in statute or the Colorado River Compact.34 limitations reflected in statute or the Colorado River Compact.34

26 Pursuant to Section 8 of the Reclamation Act of 1902 (32 Stat. 388), Reclamation is not to interfere with state laws “relating to 26 Pursuant to Section 8 of the Reclamation Act of 1902 (32 Stat. 388), Reclamation is not to interfere with state laws “relating to
the control, appropriation, use, or distribution of water used in irrigation,” and “the Secretary of the Interior, in carrying out the control, appropriation, use, or distribution of water used in irrigation,” and “the Secretary of the Interior, in carrying out
provisions of the Act, shall proceed in conformance with such laws.” However, the Court in Arizona v. Californiaprovisions of the Act, shall proceed in conformance with such laws.” However, the Court in Arizona v. California noted that the noted that the
Secretary must be able to manage the projects of the Colorado River Basin without being subject to “the varying, possibly Secretary must be able to manage the projects of the Colorado River Basin without being subject to “the varying, possibly
inconsistent, commands of the different state legislatures.” The Court therefore construed the Secretary’s authority “to permit inconsistent, commands of the different state legislatures.” The Court therefore construed the Secretary’s authority “to permit
him, within the boundaries set down in the Act, to allocate and distribute the waters of the mainstream of the Colorado River.” him, within the boundaries set down in the Act, to allocate and distribute the waters of the mainstream of the Colorado River.”
Arizona, 373 U.S. at 587, 589–90. Arizona, 373 U.S. at 587, 589–90.
27 Ibid. at 564–65. 27 Ibid. at 564–65.
28 Ibid. at 593. 28 Ibid. at 593.
29 Arizona v. California, 547 U.S. at 161–66. 29 Arizona v. California, 547 U.S. at 161–66.
30 Ibid. In addition to the Central Arizona Project legislation discussed in the next section, Arizona v. California30 Ibid. In addition to the Central Arizona Project legislation discussed in the next section, Arizona v. California also addressed also addressed
Gila River disputes between Arizona and New Mexico prior to reaching the mainstream, which is beyond the scope of this report. Gila River disputes between Arizona and New Mexico prior to reaching the mainstream, which is beyond the scope of this report.
31 Arizona v. California, 373 U.S. 31 Arizona v. California, 373 U.S. at 593-594. As the court explained, BCPA §5 serves as the basis for DOI’s authority to at 593-594. As the court explained, BCPA §5 serves as the basis for DOI’s authority to
apportion Lower Basin water deliveries. apportion Lower Basin water deliveries.
32 Ibid 32 Ibid. at 594 (allowing the Secretary, “in case of shortage,” to “adopt a method of proration” and to consider “priority of use, at 594 (allowing the Secretary, “in case of shortage,” to “adopt a method of proration” and to consider “priority of use,
local laws and customs, or any other factors that might be helpful in reaching an informed judgment in harmony with the Act, the local laws and customs, or any other factors that might be helpful in reaching an informed judgment in harmony with the Act, the
best interests of the Basin States, and the welfare of the Nation”). best interests of the Basin States, and the welfare of the Nation”).
33 Ibid33 Ibid. at 592–93. at 592–93.
34 Ibid34 Ibid. at 584 (referencing BCPA contract authority limitations including that irrigation and domestic uses are for “permanent at 584 (referencing BCPA contract authority limitations including that irrigation and domestic uses are for “permanent
service,” that nothing should disrupt compact-designated allocations between basins, and that reclamation law provisions service,” that nothing should disrupt compact-designated allocations between basins, and that reclamation law provisions
generally apply unless Congress explicitly provides otherwise); generally apply unless Congress explicitly provides otherwise); c.f. BCPA, BCPA, supra note 19. note 19.
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In 1964, the Supreme Court issued a decree implementing its opinion in In 1964, the Supreme Court issued a decree implementing its opinion in Arizona v. California.35 The .35 The
decree has been updated multiple times since, most recently in 2006.36 The decree requires the United decree has been updated multiple times since, most recently in 2006.36 The decree requires the United
States to follow specific priorities for managing water flows from federal structures based on the BCPA.37 States to follow specific priorities for managing water flows from federal structures based on the BCPA.37
In the event flows are insufficient to provide 7.5 MAF per year to the Lower Basin, the decree instructs In the event flows are insufficient to provide 7.5 MAF per year to the Lower Basin, the decree instructs
DOI to account for DOI to account for present perfected rights (i.e., water rights already in place at the time the Colorado (i.e., water rights already in place at the time the Colorado
River Compact became effective) in order of their priority dates.38 Additionally, the decree quantified River Compact became effective) in order of their priority dates.38 Additionally, the decree quantified
water rights for five tribes, although it did not address any rights or priorities of any additional Indian water rights for five tribes, although it did not address any rights or priorities of any additional Indian
Reservation.39 After consulting with states and “major” contracting parties, DOI has the authority to Reservation.39 After consulting with states and “major” contracting parties, DOI has the authority to
apportion flows pursuant to the BCPA and other statutes based on the following priority use order: apportion flows pursuant to the BCPA and other statutes based on the following priority use order:
(1) river regulation, navigation improvements, and flood control; (2) irrigation and domestic uses, (1) river regulation, navigation improvements, and flood control; (2) irrigation and domestic uses,
including the satisfaction of present perfected rights; and (3) electric power.40 The decree also identifies including the satisfaction of present perfected rights; and (3) electric power.40 The decree also identifies
specific quantities of present perfected rights and their date of recognition.41 specific quantities of present perfected rights and their date of recognition.41
Arizona v. California continues to play a significant role in Colorado River allocations. Multiple federal continues to play a significant role in Colorado River allocations. Multiple federal
statutes pertaining to Colorado River basin management refer to the statutes pertaining to Colorado River basin management refer to the Arizona v. California decree and decree and
codify its requirements.42 Following the decree, Arizona sought congressional authorization of a new codify its requirements.42 Following the decree, Arizona sought congressional authorization of a new
project to access and convey its Colorado River supplies as provided for in the Supreme Court’s decree. project to access and convey its Colorado River supplies as provided for in the Supreme Court’s decree.
Congress authorized that project in 1968, on the condition that California’s and Nevada’s water deliveries Congress authorized that project in 1968, on the condition that California’s and Nevada’s water deliveries
receive priority over Arizona’s during times of drought (see belowreceive priority over Arizona’s during times of drought (see below, “Colorado River Basin Project Act of
1968”).
. Upper Basin Compact and Colorado River Storage Project Authorizations
Congress did not allow projects originally authorized for study in the Upper Basin under BCPA to move Congress did not allow projects originally authorized for study in the Upper Basin under BCPA to move
forward with federally funded construction until the Upper Basin states determined their individual water forward with federally funded construction until the Upper Basin states determined their individual water
allocations, which occurred under the Upper Colorado River Basin Compact of 1948.43 Because there was allocations, which occurred under the Upper Colorado River Basin Compact of 1948.43 Because there was

35 Arizona v. California, 376 U.S. 340 (1964). The 1964 decree determined, among other things, that all water in the mainstream 35 Arizona v. California, 376 U.S. 340 (1964). The 1964 decree determined, among other things, that all water in the mainstream
of the Colorado River below Lee Ferry and within the United States would be “water controlled by the United States” and that of the Colorado River below Lee Ferry and within the United States would be “water controlled by the United States” and that
the Secretary would release water under only three types of designations for a year: “normal, surplus, and shortage.” the Secretary would release water under only three types of designations for a year: “normal, surplus, and shortage.”
36 The Supreme Court supplemented the 1964 decree in 1966, 1979, 1984, and 2000; in 2006 it issued a consolidated decree 36 The Supreme Court supplemented the 1964 decree in 1966, 1979, 1984, and 2000; in 2006 it issued a consolidated decree
incorporating the 1964 decree and supplements. incorporating the 1964 decree and supplements. See supra note 26. Among other things, the decrees set forth tribal water rights note 26. Among other things, the decrees set forth tribal water rights
and present perfected rights of various parties in the Lower Basin.and present perfected rights of various parties in the Lower Basin.
37 Arizona v. California, 376 U.S. 340 (1964); 547 U.S. 150 (allowing for Colorado River water releases to satisfy Mexico treaty 37 Arizona v. California, 376 U.S. 340 (1964); 547 U.S. 150 (allowing for Colorado River water releases to satisfy Mexico treaty
obligations “without regard” to the priorities specified in the BCPA as referenced in subdivision II(A) of the decree).obligations “without regard” to the priorities specified in the BCPA as referenced in subdivision II(A) of the decree).
38 Arizona v. California, 547 U.S. 150 (2006), 154–55, 166. Present perfected rights are those existing as of June 25, 1929, in 38 Arizona v. California, 547 U.S. 150 (2006), 154–55, 166. Present perfected rights are those existing as of June 25, 1929, in
accordance with state law and exercised by actually diverting a specific quantity of water and/or reservation of water rights for accordance with state law and exercised by actually diverting a specific quantity of water and/or reservation of water rights for
federal use. Ibidfederal use. Ibid. at 154. at 154.
39 Arizona v. California 39 Arizona v. California. 373 U.S. at 598–602. Indian reserved water rights were first recognized by the Supreme Court in 373 U.S. at 598–602. Indian reserved water rights were first recognized by the Supreme Court in
Winters v. United States, 207 U.S. 564, 575-77 (1908). Under the WintersWinters v. United States, 207 U.S. 564, 575-77 (1908). Under the Winters doctrine, when Congress reserves land (i.e., for an doctrine, when Congress reserves land (i.e., for an
Indian reservation), it implicitly reserves water sufficient to fulfill the purpose of the reservation. Because the establishment of Indian reservation), it implicitly reserves water sufficient to fulfill the purpose of the reservation. Because the establishment of
Indian reservations (and, therefore, of Indian water rights) generally predated large-scale development of water resources for non-Indian reservations (and, therefore, of Indian water rights) generally predated large-scale development of water resources for non-
Indian users, the water rights of tribes often are senior to those of non-Indian water rights. For more information on the resulting Indian users, the water rights of tribes often are senior to those of non-Indian water rights. For more information on the resulting
settlements, see below section, settlements, see below section, “Tribal Water Rights” and CRS Report R44148, and CRS Report R44148, Indian Water Rights Settlements. .
40 Arizona v. California, 547 U.S. 150 at 154–56 (2006). The Court did not clarify what a constituted “major delivery contract.” 40 Arizona v. California, 547 U.S. 150 at 154–56 (2006). The Court did not clarify what a constituted “major delivery contract.”
IbidIbid. at 155. at 155.
41Ibid. at 167–81 (2006). In sum, California, including tribal uses within the state, is entitled to approximately 3 MAF based on 41Ibid. at 167–81 (2006). In sum, California, including tribal uses within the state, is entitled to approximately 3 MAF based on
present perfected rights. Present perfected rights total approximately 1.05 MAF in Arizona and .000013 MAF in Nevada. present perfected rights. Present perfected rights total approximately 1.05 MAF in Arizona and .000013 MAF in Nevada.
California’s rights include Imperial Irrigation District rights to 2.6 MAF (priority date of 1901), Palo Verde Irrigation District California’s rights include Imperial Irrigation District rights to 2.6 MAF (priority date of 1901), Palo Verde Irrigation District
rights to 0.2 MAF (priority date of 1877), tribal rights totaling approximately 0.16 MAF with priority dates ranging from 1873-rights to 0.2 MAF (priority date of 1877), tribal rights totaling approximately 0.16 MAF with priority dates ranging from 1873-
1903, and an additional 0.04 MAF from other uses. 1903, and an additional 0.04 MAF from other uses.
42 See, for example, 43 U.S.C. §§1521, 1525. 42 See, for example, 43 U.S.C. §§1521, 1525.
43 Upper Colorado River Basin Compact, 1948. 43 Upper Colorado River Basin Compact, 1948.
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some uncertainty as to the exact amount of water that would remain in the system after Lower Basin some uncertainty as to the exact amount of water that would remain in the system after Lower Basin
obligations were met, the Upper Basin Compact established state allocations in terms of percentage: obligations were met, the Upper Basin Compact established state allocations in terms of percentage:
Colorado (where the largest share of runoff to the river originates) is the largest entitlement holder in the Colorado (where the largest share of runoff to the river originates) is the largest entitlement holder in the
Upper Basin, with rights to 51.75% of any Upper Basin flows after Colorado River Compact obligations Upper Basin, with rights to 51.75% of any Upper Basin flows after Colorado River Compact obligations
to the Lower Basin have been met. Other states also received percentage-based allocations, including to the Lower Basin have been met. Other states also received percentage-based allocations, including
Wyoming (14%), New Mexico (11.25%), and Utah (23%). Arizona was allocated 50,000 AF in addition Wyoming (14%), New Mexico (11.25%), and Utah (23%). Arizona was allocated 50,000 AF in addition
to its Lower Basin apportionment, in recognition of the portion of the state in the Upper to its Lower Basin apportionment, in recognition of the portion of the state in the Upper ~~Basi~~n.Basin. Figure 2
shows basin allocations by state following approval of the Upper Basin Compact (i.e., the allocations that shows basin allocations by state following approval of the Upper Basin Compact (i.e., the allocations that
generally guide current water deliveries). The Upper Basin Compact also established the Upper Colorado generally guide current water deliveries). The Upper Basin Compact also established the Upper Colorado
River Commission, an interstate administrative water agency charged with administering the provisions River Commission, an interstate administrative water agency charged with administering the provisions
of the Upper Basin Compact.44 of the Upper Basin Compact.44
Figure 2. Colorado River Basin Allocations
(shown as percentage of allocation or million acre-feet [MAF]) (shown as percentage of allocation or million acre-feet [MAF])

Source: Figure by the Congressional Research Service (CRS), using data from USGS, ESRI Data & Maps, 2017, Central Figure by the Congressional Research Service (CRS), using data from USGS, ESRI Data & Maps, 2017, Central
Arizona Project, and ESRI World Shaded Relief Map. Arizona Project, and ESRI World Shaded Relief Map.

44 For more information, see Upper Colorado River Commission, “About the UCRC,” at http://www.ucrcommission.com/about- 44 For more information, see Upper Colorado River Commission, “About the UCRC,” at http://www.ucrcommission.com/about-
us/. us/.
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Notes: Although both the Upper and Lower Basins were each allocated 7.5 MAF, there was uncertainty about how much Although both the Upper and Lower Basins were each allocated 7.5 MAF, there was uncertainty about how much
water would remain in the Upper Basin after Colorado River Compact obligations to Lower Basin states were water would remain in the Upper Basin after Colorado River Compact obligations to Lower Basin states were ~~fulfil ed~~fulfilled. .
Therefore, outside of 50,000 AF provided annually to Arizona, the Upper Basin Compact includes apportionments in Therefore, outside of 50,000 AF provided annually to Arizona, the Upper Basin Compact includes apportionments in
terms of percentage of the overall Upper Basin allocation. terms of percentage of the overall Upper Basin allocation.
Subsequent federal legislation paved the way for development of Upper Basin waters. The Colorado Subsequent federal legislation paved the way for development of Upper Basin waters. The Colorado
River Storage Project (CRSP) Act of 1956 authorized CRSP River Storage Project (CRSP) Act of 1956 authorized CRSP initial units of Glen Canyon, Flaming Gorge, of Glen Canyon, Flaming Gorge,
Navajo, and Aspinall in the Upper Basin. The act also established the Upper Colorado River Basin Fund, Navajo, and Aspinall in the Upper Basin. The act also established the Upper Colorado River Basin Fund,
which receives revenues collected in connection with the projects, to be made available for defraying the which receives revenues collected in connection with the projects, to be made available for defraying the
project’s costs of operation, maintenance, and emergency expenditures. project’s costs of operation, maintenance, and emergency expenditures.
Colorado River Basin Project Act of 1968
The Colorado River Basin Project Act (CRBPA), enacted in 1968, authorized additional projects in both The Colorado River Basin Project Act (CRBPA), enacted in 1968, authorized additional projects in both
the Upper and Lower Basins and made other changes to basin management. In the CRBPA, Congress the Upper and Lower Basins and made other changes to basin management. In the CRBPA, Congress
authorized a major new water conveyance project in Arizona, the Central Arizona Project (CAP),45 as well authorized a major new water conveyance project in Arizona, the Central Arizona Project (CAP),45 as well
as several other Upper Basin projects (e.g., the Animas La Plata and Central Utah projects). The CRBPA as several other Upper Basin projects (e.g., the Animas La Plata and Central Utah projects). The CRBPA
also established funding mechanisms for revenues from power generation from relevant Upper and Lower also established funding mechanisms for revenues from power generation from relevant Upper and Lower
Basin facilities to be used to fund specific expenses in each respective basin. The act also provided Basin facilities to be used to fund specific expenses in each respective basin. The act also provided
direction on how to address shortages in the Lower Basin when the Colorado River cannot supply annual direction on how to address shortages in the Lower Basin when the Colorado River cannot supply annual
consumptive use of 7.5 MAF in Arizona, California, and Nevada.46 consumptive use of 7.5 MAF in Arizona, California, and Nevada.46
The CRBPA represented a legislative compromise between the interests of California and Arizona. The The CRBPA represented a legislative compromise between the interests of California and Arizona. The
act authorized the CAP but provides that, in the event of shortage conditions, California’s 4.4 MAF act authorized the CAP but provides that, in the event of shortage conditions, California’s 4.4 MAF
allocation would have priority over CAP water supplies.47 Specifically, when there are shortages, the allocation would have priority over CAP water supplies.47 Specifically, when there are shortages, the
CRBPA directs that diversions to the CAP are to be limited to ensure sufficient consumptive use for CRBPA directs that diversions to the CAP are to be limited to ensure sufficient consumptive use for
certain California and Nevada users whose water rights predate the CAP, consistent with the 1964 certain California and Nevada users whose water rights predate the CAP, consistent with the 1964 Arizona
v. California decree decree.48 48
In addition, the CRBPA directs the Secretary of the Interior to develop a plan for meeting future water In addition, the CRBPA directs the Secretary of the Interior to develop a plan for meeting future water
needs, develop criteria for operating federally authorized reservoirs in the basin to ensure that the needs, develop criteria for operating federally authorized reservoirs in the basin to ensure that the
reservoirs satisfy existing needs and legal obligations, and report annually on implementation of the reservoirs satisfy existing needs and legal obligations, and report annually on implementation of the
plan.49 Section 602 of the CRBPA directs the Secretary of the Interior to consultatively develop plan.49 Section 602 of the CRBPA directs the Secretary of the Interior to consultatively develop
operational criteria—known as operational criteria—known as Long-Range Operating Criteria (LROC)—for federally authorized (LROC)—for federally authorized
Colorado River reservoirs in the following order of priority: (1) treaty obligations to Mexico, (2) the Colorado River reservoirs in the following order of priority: (1) treaty obligations to Mexico, (2) the
Colorado River Compact requirement for the Upper Basin to not deplete more than 75 MAF to Lower Colorado River Compact requirement for the Upper Basin to not deplete more than 75 MAF to Lower
Basin states over any 10-year period, and (3) carryover storage to meet these needs.50 The Secretary of the Basin states over any 10-year period, and (3) carryover storage to meet these needs.50 The Secretary of the

45 See 45 See 43 U.S.C. §§1501–1556. The Central Arizona Project was authorized in 43 U.S.C. §1521. Some portions of the Colorado 43 U.S.C. §§1501–1556. The Central Arizona Project was authorized in 43 U.S.C. §1521. Some portions of the Colorado
River Basin Project Act (CRBPA) were codified as amendments to the CRSPA. IbidRiver Basin Project Act (CRBPA) were codified as amendments to the CRSPA. Ibid. §§620a, 620a-1. §§620a, 620a-1.
46 Ibid. 46 Ibid.
47 43 U.S.C. §1521. 47 43 U.S.C. §1521.
48 See48 See 43 U.S.C. §1525 (allowing for limitations to Arizona supplies sufficient to enable 4.4 MAF of annual consumption “by 43 U.S.C. §1525 (allowing for limitations to Arizona supplies sufficient to enable 4.4 MAF of annual consumption “by
holders of present perfected rights, by other users in the State of California served under existing contracts with the United States holders of present perfected rights, by other users in the State of California served under existing contracts with the United States
by diversion works heretofore constructed, and by other existing Federal reservations in that State, and by users of the same by diversion works heretofore constructed, and by other existing Federal reservations in that State, and by users of the same
character in Arizona and Nevada”). Note that the legislation references Section II(B)(1) of the Arizona v. California 1964 character in Arizona and Nevada”). Note that the legislation references Section II(B)(1) of the Arizona v. California 1964
Supreme Court decree, 376 U.S. 340, which is associated with the 1963 opinion SectionSupreme Court decree, 376 U.S. 340, which is associated with the 1963 opinion Section III, Apportionment and Contracts in III, Apportionment and Contracts in
Time of Shortage, 373 U.S. 546, 592-94. See alsoTime of Shortage, 373 U.S. 546, 592-94. See also 43 U.S.C. §1521(b) (allowing modifications to Central Arizona Project 43 U.S.C. §1521(b) (allowing modifications to Central Arizona Project
diversions).diversions).
49 Ibid 49 Ibid. §§1501(b), 1552. §§1501(b), 1552.
50 Ibid. §1552(a)-(b). The Grand Canyon Protection Act (P.L. 102-575) directs DOI to operate Glen Canyon Dam in a specific 50 Ibid. §1552(a)-(b). The Grand Canyon Protection Act (P.L. 102-575) directs DOI to operate Glen Canyon Dam in a specific
manner. In addition to compliance with laws governing Colorado River water apportionment, DOI must adopt criteria and manner. In addition to compliance with laws governing Colorado River water apportionment, DOI must adopt criteria and
operating plans separate from and in addition to the ones specified in Section 602 of the CRBPA consistent with Grand Canyon operating plans separate from and in addition to the ones specified in Section 602 of the CRBPA consistent with Grand Canyon
(continued...) (continued...)
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Interior may modify the criteria based on “actual operating experience or unforeseen circumstances” after Interior may modify the criteria based on “actual operating experience or unforeseen circumstances” after
correspondence and consultation with representatives of the basin states.51 The Secretary of the Interior correspondence and consultation with representatives of the basin states.51 The Secretary of the Interior
first adopted LROC in 1970; they were last modified in 2005.52 first adopted LROC in 1970; they were last modified in 2005.52
Water Storage and Operations
The Colorado River Basin’s large water storage projects can store as much as 60 MAF, or about four The Colorado River Basin’s large water storage projects can store as much as 60 MAF, or about four
times the Colorado River’s annual flows, to insulate water users from annual variability in flows. Thus, times the Colorado River’s annual flows, to insulate water users from annual variability in flows. Thus,
storage and operations in the basin receive considerable attention, particularly at the basin’s two largest storage and operations in the basin receive considerable attention, particularly at the basin’s two largest
dams and their storage reservoirs: Glen Canyon Dam/Lake Powell in the Upper Basin (26.2 MAF of dams and their storage reservoirs: Glen Canyon Dam/Lake Powell in the Upper Basin (26.2 MAF of
storage capacity) and Hoover Dam/Lake Mead in the Lower Basin (26.1 MAF of storage capacity). The storage capacity) and Hoover Dam/Lake Mead in the Lower Basin (26.1 MAF of storage capacity). The
status of these projects is monitored closely by Reclamation and interested stakeholders as an indicator of status of these projects is monitored closely by Reclamation and interested stakeholders as an indicator of
basin health. basin health.
Glen Canyon Dam, completed in 1963 at the southern end of the Upper Basin, serves as the linchpin for Glen Canyon Dam, completed in 1963 at the southern end of the Upper Basin, serves as the linchpin for
Upper Basin storage and regulates flows from the Upper Basin to the Lower Basin, pursuant to the Upper Basin storage and regulates flows from the Upper Basin to the Lower Basin, pursuant to the
Colorado River Compact. From 2000 to 2020, it generated an average of approximately 3.8 billion Colorado River Compact. From 2000 to 2020, it generated an average of approximately 3.8 billion
kilowatt-hours (KWh) of electricity per year, which the Western Area Power Administration (WAPA) kilowatt-hours (KWh) of electricity per year, which the Western Area Power Administration (WAPA)
supplies to 5.8 million customers in Upper Basin States.53 Other significant storage in the Upper Basin supplies to 5.8 million customers in Upper Basin States.53 Other significant storage in the Upper Basin
includes the initial units of the CRSP: the Aspinall Unit in Colorado (including Blue Mesa, Crystal, and includes the initial units of the CRSP: the Aspinall Unit in Colorado (including Blue Mesa, Crystal, and
Morrow Point dams on the Gunnison River, with combined storage capacity of more than 1 MAF),54 the Morrow Point dams on the Gunnison River, with combined storage capacity of more than 1 MAF),54 the
Flaming Gorge Unit in Utah (including Flaming Gorge Dam on the Green River, with a capacity of 3.8 Flaming Gorge Unit in Utah (including Flaming Gorge Dam on the Green River, with a capacity of 3.8
MAF), and the Navajo Unit in New Mexico (including Navajo Dam on the San Juan River, with a MAF), and the Navajo Unit in New Mexico (including Navajo Dam on the San Juan River, with a
capacity of 1 MAF). The Upper Basin is also home to 16 participating projects, which are authorized to capacity of 1 MAF). The Upper Basin is also home to 16 participating projects, which are authorized to
use water for irrigation, M&I uses, and other purposes.55 use water for irrigation, M&I uses, and other purposes.55
Hoover Dam, completed in 1936, provides the majority of the Lower Basin’s storage and generates on Hoover Dam, completed in 1936, provides the majority of the Lower Basin’s storage and generates on
average about 4 billion KWh of electricity per year for customers in California, Arizona, and Nevada.56 average about 4 billion KWh of electricity per year for customers in California, Arizona, and Nevada.56
Also important for Lower Basin Operations are Davis Dam/Lake Mohave, which regulates flows to Also important for Lower Basin Operations are Davis Dam/Lake Mohave, which regulates flows to
Mexico under the 1944 Treaty, and Parker Dam/Lake Havasu, which impounds water for diversion into Mexico under the 1944 Treaty, and Parker Dam/Lake Havasu, which impounds water for diversion into
the Colorado River Aqueduct (thereby allowing for deliveries to urban areas in Southern California) and the Colorado River Aqueduct (thereby allowing for deliveries to urban areas in Southern California) and
CAP (allowing for diversion to users in Arizona). Further downstream on the Arizona/California border, CAP (allowing for diversion to users in Arizona). Further downstream on the Arizona/California border,

National Park values. However, the legislation states that the provisions are not intended to affect state water rights to Colorado National Park values. However, the legislation states that the provisions are not intended to affect state water rights to Colorado
River allocations that have been secured by “any compact, law, or decree.” P.L. 102-575, §1802, 106 Stat. 4669 (1992). The River allocations that have been secured by “any compact, law, or decree.” P.L. 102-575, §1802, 106 Stat. 4669 (1992). The
CRBPA provides that if the federal government fails to comply with applicable law in operating Glen Canyon Dam, any affected CRBPA provides that if the federal government fails to comply with applicable law in operating Glen Canyon Dam, any affected
state can sue to enforce its provisions in the Supreme Court. 43 U.S.C. §1551(c). state can sue to enforce its provisions in the Supreme Court. 43 U.S.C. §1551(c).
51 Ibid 51 Ibid.
52 Operating Criteria, 70 52 Operating Criteria, 70 Federal Register 15,873 (Mar. 29, 2005); Colorado River Reservoirs, Coordinated Long-Range 15,873 (Mar. 29, 2005); Colorado River Reservoirs, Coordinated Long-Range
Operations, 35 Operations, 35 Federal Register 8951 (June 10, 1970). Through later legislation, Congress required that, in preparing the LROC 8951 (June 10, 1970). Through later legislation, Congress required that, in preparing the LROC
and Annual Operating Plan, the Secretary of the Interior must consult the governors of the basin states and with the public, seeand Annual Operating Plan, the Secretary of the Interior must consult the governors of the basin states and with the public, see
Grand Canyon Protection Act of 1992, P.L. 102-575, §1804(c)(3), 106 Stat. 4669. Grand Canyon Protection Act of 1992, P.L. 102-575, §1804(c)(3), 106 Stat. 4669.
53 Statement of Bureau of Reclamation Commissioner Camille Calimlim Touton, in U.S. Congress, Senate Committee on Energy 53 Statement of Bureau of Reclamation Commissioner Camille Calimlim Touton, in U.S. Congress, Senate Committee on Energy
and Natural Resources, Subcommittee on Water and Power, 117th Cong., 2nd sess., May 25, 2022. For a more detailed discussion and Natural Resources, Subcommittee on Water and Power, 117th Cong., 2nd sess., May 25, 2022. For a more detailed discussion
of the effects of long-term drought on Glen Canyon Dam, see CRS Report R47497, of the effects of long-term drought on Glen Canyon Dam, see CRS Report R47497, Long-Term Drought and Glen Canyon Dam:
Potential Effects on Water Deliveries and Hydropower, by Charles V. Stern and Ashley J. Lawson. , by Charles V. Stern and Ashley J. Lawson.
54 The Curecanti Unit was renamed the Aspinall Unit in 1980 in honor of U.S. Representative Wayne N. Aspinall of Colorado. 54 The Curecanti Unit was renamed the Aspinall Unit in 1980 in honor of U.S. Representative Wayne N. Aspinall of Colorado.
55 In total, 16 of the 22 Upper Basin projects authorized as part of CRSP have been developed. (Of the six remaining projects, 55 In total, 16 of the 22 Upper Basin projects authorized as part of CRSP have been developed. (Of the six remaining projects,
five were determined by Reclamation to be infeasible, and Congress deauthorized the the Pine River Extension Project.) For a five were determined by Reclamation to be infeasible, and Congress deauthorized the the Pine River Extension Project.) For a
complete list of projects, see Bureau of Reclamation, “Colorado River Storage Project,” at https://www.usbr.gov/uc/rm/crsp/complete list of projects, see Bureau of Reclamation, “Colorado River Storage Project,” at https://www.usbr.gov/uc/rm/crsp/
index.html. index.html.
56 Reclamation, “Hoover Dam Frequently Asked Questions and Answers,” at https://www.usbr.gov/lc/hooverdam/faqs/ 56 Reclamation, “Hoover Dam Frequently Asked Questions and Answers,” at https://www.usbr.gov/lc/hooverdam/faqs/
powerfaq.html, accessed powerfaq.html, accessed ~~August 3, 2022~~October 30, 2023. .
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Imperial Dam (a diversion dam) diverts Colorado River water to the All-American Canal for use in some Imperial Dam (a diversion dam) diverts Colorado River water to the All-American Canal for use in some
of the river’s largest agricultural areas in California’s Imperial and Coachella Valleys. of the river’s largest agricultural areas in California’s Imperial and Coachella Valleys.
Annual Operations
Reclamation monitors Colorado River reservoir levels and projects them 24 months into the future in Reclamation monitors Colorado River reservoir levels and projects them 24 months into the future in
monthly studies (called monthly studies (called 24-month studies).57 The studies take into account forecasted hydrology, reservoir ).57 The studies take into account forecasted hydrology, reservoir
operations, and diversion and consumptive use schedules to model a single scenario of reservoir operations, and diversion and consumptive use schedules to model a single scenario of reservoir
conditions. The studies inform operating decisions by Reclamation looking one to two years into the conditions. The studies inform operating decisions by Reclamation looking one to two years into the
future. They express water storage conditions at Lake Mead and Lake Powell in terms of elevation, as feet future. They express water storage conditions at Lake Mead and Lake Powell in terms of elevation, as feet
above mean sea level. above mean sea level.
In addition to the 24-month studies, the CRBPA requires the Secretary of the Interior to transmit to In addition to the 24-month studies, the CRBPA requires the Secretary of the Interior to transmit to
Congress and the governors of the basin states, by January 1 of each year, an Congress and the governors of the basin states, by January 1 of each year, an Annual Operating Plan
(AOP). In the AOP, Reclamation describes the actual operation for the preceding water year and the (AOP). In the AOP, Reclamation describes the actual operation for the preceding water year and the
projected operation for the coming year. The AOP’s projected January 1 water conditions for the projected operation for the coming year. The AOP’s projected January 1 water conditions for the
upcoming calendar year establish a baseline for future annual operations.58 upcoming calendar year establish a baseline for future annual operations.58
Since the adoption of operational guidelines by Reclamation and basin states in 2007 (see below section, Since the adoption of operational guidelines by Reclamation and basin states in 2007 (see below section,
“2007 Interim Guidelines”~~), Reclamation~~), Reclamation has tied operations of Hoover and Glen Canyon Dams to has tied operations of Hoover and Glen Canyon Dams to
specific pool elevations at Lake Mead and Lake Powell. For Lake Mead, the first level of shortage (a specific pool elevations at Lake Mead and Lake Powell. For Lake Mead, the first level of shortage (a Tier
One Shortage Condition) in the 2007 guidelines, under which Arizona’s and Nevada’s allocations are ) in the 2007 guidelines, under which Arizona’s and Nevada’s allocations are
curtailments (along with releases to Mexico), is triggered if the Lake Mead pool elevation falls below curtailments (along with releases to Mexico), is triggered if the Lake Mead pool elevation falls below
1,075 feet. For Lake Powell, releases under tiered operations are based on storage levels in both Lake 1,075 feet. For Lake Powell, releases under tiered operations are based on storage levels in both Lake
Powell and Lake Mead. Drought contingency plans (DCPs) for the Upper and Lower Basins, enacted in Powell and Lake Mead. Drought contingency plans (DCPs) for the Upper and Lower Basins, enacted in
2019, overlaid additional operational changes tied to elevations in both reservoirs2019, overlaid additional operational changes tied to elevations in both reservoirs~~. For Lake Mead, this~~
~~included additional curtailments beyond those established in 2007~~, including a new Tier Zero shortage beginning at a higher reservoir elevation (up to 1,090 feet) and additional curtailments for other existing tiers (e.g., Tier Two, etc.).59 For Lake Powell, the Upper Basin .59 For Lake Powell, the Upper Basin
DCP incorporated a Drought Response Operations Agreement (DROA) that established a target lake DCP incorporated a Drought Response Operations Agreement (DROA) that established a target lake
elevation of 3,525 feet. It also provided for altered releases from Glen Canyon Dam and Upper Basin elevation of 3,525 feet. It also provided for altered releases from Glen Canyon Dam and Upper Basin
reservoirs in order to protect Lake Powell from falling below an elevation that would no longer produce reservoirs in order to protect Lake Powell from falling below an elevation that would no longer produce
hydropower. These efforts are discussed more in the below section hydropower. These efforts are discussed more in the below section “Recent Developments and
Agreements.”
Recent Conditions
~~Falling~~Since 2020, falling water levels in Lake Mead water levels in Lake Mead ~~have~~ resulted in Reclamation resulted in Reclamation ~~announcing~~implementing Lower Colorado River Basin Lower Colorado River Basin
delivery curtailments for Arizona and Nevadadelivery curtailments for Arizona and Nevada~~, in accordance with previous plans. In August 2021,~~
~~Reclamation declared the first-ever Tier One Shortage Condition for the Lower Basin.60 In August 2022,~~
~~Reclamation announced the first-ever Tier Two Shortage, which resulted in additional water supply~~ in accordance with previous plans (Table 1). Water year 2020 triggered a Tier Zero reduction, as agreed to in the 2019 DCPs. In August 2021, Reclamation declared the first-ever Tier One Shortage Condition for the Lower Basin in Water Year 2022.60 In August 2022 Reclamation cut deliveries further, announcing a Tier Two Shortage for 2023, resulting in additional water supply delivery cutbacks in that year.61 For 2024, Reclamation forecasts

57 Current 24-month studies, as well as two- and five-year probable projections of Lake Mead and Powell elevations, are 57 Current 24-month studies, as well as two- and five-year probable projections of Lake Mead and Powell elevations, are
available at Reclamation, “Colorado River System Projections Overview,” at https://www.usbr.gov/lc/region/g4000/riverops/available at Reclamation, “Colorado River System Projections Overview,” at https://www.usbr.gov/lc/region/g4000/riverops/
coriver-projections.html. coriver-projections.html.
58 Current and historical AOPs are available at Reclamation, “Annual Operating Plan for Colorado River Reservoirs,” at 58 Current and historical AOPs are available at Reclamation, “Annual Operating Plan for Colorado River Reservoirs,” at
https://www.usbr.gov/uc/water/rsvrs/ops/aop/. https://www.usbr.gov/uc/water/rsvrs/ops/aop/.
59 For 59 For ~~example, a new set of curtailments for Nevada and Arizona at lake elevations up to 1,090 feet (Tier Zero) was added~~
~~pursuant to the 2019 DCP for the Lower Colorado River Basin. These agreements also added additional curtailment requirements~~
~~to existing Tiers below Tier 1 (e.g., Tier 2, etc.). For more details, see Table 1.~~
~~60 Reclamation, “Reclamation Announces 2022~~more details, see below section, “Lower Basin Drought Contingency Plan”. 60 Reclamation, “Reclamation Announces 2022 Operating Conditions for Lake Powell and Lake Mead,” press release, August 16, 2021, at https://www.usbr.gov/newsroom/#/news-release/3950. 61 Reclamation, “Interior Department Announces Actions to Protect Colorado River System, Sets 2023 Operating Conditions for Lake Powell and Lake Mead,” press release, August 16, Operating Conditions for Lake Powell and Lake Mead,” press release, August 16,
~~2021~~2022, at https://www.usbr.gov/newsroom/, at https://www.usbr.gov/newsroom/#/news-release/news-release/~~3950.~~
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~~delivery cutbacks.61 In March 2022~~annual operations under a Level 1 shortage condition (i.e., fewer cutbacks than in Water Year 2023) as a result of improved hydrology and other conservation efforts.62 For its part, in 2022 and early 2023, Lake Powell fell below the target elevation of 3,525 feet, which had , Lake Powell fell below the target elevation of 3,525 feet, which had
not occurred since the late 1960s.not occurred since the late 1960s.6263 However, Lake Powell levels rebounded in 2023 compared with 2022. Table 1. Lower Basin Lake Mead Operational Tiers by Year, 2020-2024 (water delivery curtailments in terms of thousand acre-feet [KAF]) Cumulative Delivery Curtailments by State by KAF (percentage of total deliveries) Operational Year Tier Arizona California Nevada 2020 Zero 192 (6.8%) - 8 (2.6%) 2021 Zero 192 (6.8%) - 8 (2.6%) 2022 One 512 (18.2%) - 21 (7.0%) 2023 Two 592 (21.1%) - 25 (8.3%) 2024 (forecast) One 512 (18.2%) - 21 (7.0%) Source: CRS, based on information from the Bureau of Reclamation, 2019-2023.
Mitigating the Environmental Effects of Colorado River
Basin Development
Construction of most of the Colorado River’s water supply infrastructure predated major federal Construction of most of the Colorado River’s water supply infrastructure predated major federal
environmental protection statutes, such as the National Environmental Policy Act (NEPA; 42 U.S.C. environmental protection statutes, such as the National Environmental Policy Act (NEPA; 42 U.S.C.
§§4321 et seq.) and the ESA. Thus, many of the environmental impacts associated with the development §§4321 et seq.) and the ESA. Thus, many of the environmental impacts associated with the development
of basin resources were not originally taken into account. Over time, multiple efforts have been initiated of basin resources were not originally taken into account. Over time, multiple efforts have been initiated
to mitigate these effects. Some of the highest-profile efforts have been associated with water quality (in to mitigate these effects. Some of the highest-profile efforts have been associated with water quality (in
particular, salinity control) and the effects of facility operations on endangered and threatened species.particular, salinity control) and the effects of facility operations on endangered and threatened species.
These efforts are discussed below. Salinity Control
Salinity and water quality are long-standing issues in the Colorado River Basin. Parts of the Upper Basin Salinity and water quality are long-standing issues in the Colorado River Basin. Parts of the Upper Basin
are covered by salt-bearing shale (which increases salt content of water inflows), and salinity content are covered by salt-bearing shale (which increases salt content of water inflows), and salinity content
increases as the river flows downstream due to both natural leaching and return flows from agricultural increases as the river flows downstream due to both natural leaching and return flows from agricultural
irrigation. The 1944 U.S.-Mexico Water Treaty did not set water quality or salinity standards in the irrigation. The 1944 U.S.-Mexico Water Treaty did not set water quality or salinity standards in the
Colorado River Basin. After years of dispute between the United States and Mexico regarding the salinity Colorado River Basin. After years of dispute between the United States and Mexico regarding the salinity
of the water reaching Mexico’s border, the two countries reached an agreement on August 30, 1973, with of the water reaching Mexico’s border, the two countries reached an agreement on August 30, 1973, with
the signing of Minute 242 of the International Boundary and Water Commission.the signing of Minute 242 of the International Boundary and Water Commission.6364 The agreement The agreement
guarantees Mexico that the average salinity of its treaty deliveries will be no more than 115 parts perguarantees Mexico that the average salinity of its treaty deliveries will be no more than 115 parts per
~~million higher than the salinity content of the water diverted to the All-American Canal at Imperial Dam~~
~~in Southern California. To control the salinity of Colorado River water in accordance with this agreement,~~
~~Congress passed the Colorado River Basin Salinity Control Act of 1974, which authorized desalting and~~
~~salinity control facilities to improve Colorado River water quality. The most prominent of these facilities~~
~~is the Yuma Desalting Plant, which was largely completed in 1992 but has never operated at capacity due~~
~~to cost and other factors.64 In 1974, the seven basin states also established water quality standards for~~
~~salinity through the Colorado River Basin Salinity Control Forum.65~~

~~61 Reclamation, “Interior Department Announces Actions to Protect Colorado River System, Sets 2023 Operating Conditions for~~
62 Reclamation, “Reclamation announces 2024 operating conditions for Lake Powell and Lake Mead,” press release, August Lake Powell and Lake Mead,” press release, August ~~16, 2022~~15, 2023, at https://www.usbr.gov/newsroom/news-release/, at https://www.usbr.gov/newsroom/news-release/~~4294.~~
624603. 63 Reclamation, “Lake Powell to Temporarily Decline Below 3,525 Feet,” press release, March 4, 2022, at https://www.usbr.gov/ Reclamation, “Lake Powell to Temporarily Decline Below 3,525 Feet,” press release, March 4, 2022, at https://www.usbr.gov/
newsroom/#/news-release/4117. 3,525 feet is established as a target because it is 35 feet above 3,490 feet, or the level at which newsroom/#/news-release/4117. 3,525 feet is established as a target because it is 35 feet above 3,490 feet, or the level at which
power production would cease. power production would cease.
6364 See International Boundary and Water Commission, See International Boundary and Water Commission, Minute 242, Permanent and Definitive Solution to the International
Problem of the Salinity of the Colorado River, August 30, 1973, at https://www.ibwc.gov/Treaties_Minutes/Minutes.html. , August 30, 1973, at https://www.ibwc.gov/Treaties_Minutes/Minutes.html.
~~64 The Yuma Desalting Plant’s limited operations have been due in part to the cost of its operations (desalination can require~~
~~considerable electricity to operate) and surplus flows in the Colorado River during some years. In lieu of operating the plant,~~
~~high-salinity irrigation water has been separated from the United States’ required deliveries to Mexico and disposed of through a~~
~~canal that enters Mexico and discharges into wetlands called the Ciénega de Santa Clara, near the Gulf of California. Whether~~
~~and how the plant should be operated and how the impacts on the Ciénega de Santa Clara from the untreated irrigation runoff~~
~~should be managed remain topics of some debate in the basin and between Mexico and the United States.~~
~~65 Additional information about the forum and related salinity control efforts is available at Colorado River Basin, “Salinity~~
~~Control Forum,” at https://www.coloradoriversalinity.org/.~~
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~~Endangered Species Efforts and Habitat Improvements~~
~~Congress enacted the ESA in 1973.66 As the federal government listed some basin species under ESA in~~
~~accordance with the act,67~~Congressional Research Service 12 Management of the Colorado River: Water Allocations, Drought, and the Federal Role million higher than the salinity content of the water diverted to the All-American Canal at Imperial Dam in Southern California. To control the salinity of Colorado River water in accordance with this agreement, Congress passed the Colorado River Basin Salinity Control Act of 1974, which authorized desalting and salinity control facilities to improve Colorado River water quality. The most prominent of these facilities is the Yuma Desalting Plant, which was largely completed in 1992 but has never operated at capacity due to cost and other factors.65 In 1974, the seven basin states also established water quality standards for salinity through the Colorado River Basin Salinity Control Forum.66 Endangered Species Efforts and Habitat Improvements Congress enacted the ESA in 1973.67 As the federal government listed some basin species under ESA in accordance with the act,68 federal agencies and nonfederal stakeholders consulted with the U.S. Fish and federal agencies and nonfederal stakeholders consulted with the U.S. Fish and
Wildlife Service (FWS) to address the conservation of the listed species. As a result of these Wildlife Service (FWS) to address the conservation of the listed species. As a result of these
consultations, several major programs have been developed to protect and restore listed fish species on consultations, several major programs have been developed to protect and restore listed fish species on
the Colorado River and its tributaries. Summaries of some of the key programs are below. the Colorado River and its tributaries. Summaries of some of the key programs are below.
Upper Colorado Endangered Fish Recovery Program
The Upper Colorado Endangered Fish Recovery Program was established in 1988 to assist in the recovery The Upper Colorado Endangered Fish Recovery Program was established in 1988 to assist in the recovery
of four species of endangered fish in the Upper Colorado River Basin.of four species of endangered fish in the Upper Colorado River Basin.6869 Congress formally authorized this Congress formally authorized this
program in 2000.program in 2000.6970 The program is implemented through several stakeholders under a cooperative The program is implemented through several stakeholders under a cooperative
agreement signed by the governors of Colorado, Utah, and Wyoming; the Secretary of the Interior; and agreement signed by the governors of Colorado, Utah, and Wyoming; the Secretary of the Interior; and
the Administrator of WAPA. The recovery goals of the program are to reduce threats to species and the Administrator of WAPA. The recovery goals of the program are to reduce threats to species and
improve their status so they are eventually delisted from the ESA. Some of the actions taken in the past improve their status so they are eventually delisted from the ESA. Some of the actions taken in the past
include providing adequate instream flows for fish and their habitat, restoring habitat, reducing nonnative include providing adequate instream flows for fish and their habitat, restoring habitat, reducing nonnative
fish, augmenting fish populations with stocked fish, and conducting research and monitoring. fish, augmenting fish populations with stocked fish, and conducting research and monitoring.
Reclamation is the lead federal agency for the program and provides the majority of federal funds for Reclamation is the lead federal agency for the program and provides the majority of federal funds for
implementation. Other funding includes a portion of Upper Basin hydropower revenues from WAPA and implementation. Other funding includes a portion of Upper Basin hydropower revenues from WAPA and
funding from FWS; the states of Colorado, Wyoming, and Utah; and water users, among others. funding from FWS; the states of Colorado, Wyoming, and Utah; and water users, among others.
~~San Juan River Basin Recovery Implementation Program~~
~~The San Juan River Basin Recovery Implementation Program was established in 1992 to assist in the~~
~~recovery of ESA-listed fish species on the San Juan River, the Colorado’s largest tributary.70 The program~~
~~is a partnership implemented under a cooperative agreement between DOI and the states of Colorado and~~
~~New Mexico, the Jicarilla Apache Nation, the Navajo Nation, the Southern Ute Indian Tribe, and the Ute~~
~~Mountain Ute Indian Tribe.71 It is concerned with the recovery of the Razorback sucker (~~~~Xyrauchen~~
~~texanus) and Colorado pikeminnow (Ptychocheilus Lucius). Congress authorized this program in with the~~
~~aim to protect the genetic integrity and population of listed species, conserve and restore habitat~~
~~(including water quality), reduce nonnative species, and monitor species. The program is coordinated by~~
~~FWS, and Reclamation is responsible for operating the Animas-La Plata Project and Navajo Dam on the~~
~~San Juan River in a way that reduces effects on the fish populations. The program is funded by a portion~~
~~of revenues from hydropower revenues from WAPA in the Upper Basin, Reclamation, the Bureau of~~
~~Indian Affairs, and participating states. Recovery efforts for listed fish are coordinated with the Upper~~
~~Colorado Endangered Fish Recovery Program.~~

66 65 The Yuma Desalting Plant’s limited operations have been due in part to the cost of its operations (desalination can require considerable electricity to operate) and surplus flows in the Colorado River during some years. In lieu of operating the plant, high-salinity irrigation water has been separated from the United States’ required deliveries to Mexico and disposed of through a canal that enters Mexico and discharges into wetlands called the Ciénega de Santa Clara, near the Gulf of California. Whether and how the plant should be operated and how the impacts on the Ciénega de Santa Clara from the untreated irrigation runoff should be managed remain topics of some debate in the basin and between Mexico and the United States. 66 Additional information about the forum and related salinity control efforts is available at Colorado River Basin, “Salinity Control Forum,” at https://www.coloradoriversalinity.org/. 67 For background information on the Endangered Species Act (87 Stat. 884, 16 U.S.C. §§1531-1544), see CRS Report R46677, For background information on the Endangered Species Act (87 Stat. 884, 16 U.S.C. §§1531-1544), see CRS Report R46677,
The Endangered Species Act: Overview and Implementation. .
6768 Several listed species are found throughout the Colorado River Basin. Some are specifically found in the Colorado River, such Several listed species are found throughout the Colorado River Basin. Some are specifically found in the Colorado River, such
as the Razorback sucker (as the Razorback sucker (Xyrauchen texanus), Bonytail chub (), Bonytail chub (Gila elegans), Colorado pikeminnow (), Colorado pikeminnow (Ptychocheilus Lucius), and ), and
Humpback chub (Humpback chub (Gila cypha). Consultation about an agency action’s effects on these species is required by 16 U.S.C. §1536(a). ). Consultation about an agency action’s effects on these species is required by 16 U.S.C. §1536(a).
6869 The fish species are the humpback chub, bonytail, Colorado pikeminnow and razorback sucker. For more information, see The fish species are the humpback chub, bonytail, Colorado pikeminnow and razorback sucker. For more information, see
Upper Colorado River Endangered Fish Recovery Program at http://www.coloradoriverrecovery.org/uc. Upper Colorado River Endangered Fish Recovery Program at http://www.coloradoriverrecovery.org/uc.
~~69 P.L. 106-392.~~
~~70 For more information, see U.S. Fish and Wildlife Service, “San Juan River Basin Recovery Implementation Program,” at~~
~~https://www.fws.gov/southwest/sjrip/.~~
~~71 It also includes participation by water development interests in~~70 P.L. 106-392. Congressional Research Service 13 Management of the Colorado River: Water Allocations, Drought, and the Federal Role San Juan River Basin Recovery Implementation Program The San Juan River Basin Recovery Implementation Program was established in 1992 to assist in the recovery of ESA-listed fish species on the San Juan River, the Colorado’s largest tributary.71 The program is a partnership implemented under a cooperative agreement between DOI and the states of Colorado and Colorado and New Mexico, the Jicarilla Apache Nation, the Navajo Nation, the Southern Ute Indian Tribe, and the Ute Mountain Ute Indian Tribe.72 It is concerned with the recovery of the Razorback sucker (Xyrauchen texanus) and Colorado pikeminnow (Ptychocheilus Lucius). Congress authorized this program in with the aim to protect the genetic integrity and population of listed species, conserve and restore habitat (including water quality), reduce nonnative species, and monitor species. The program is coordinated by FWS, and Reclamation is responsible for operating the Animas-La Plata Project and Navajo Dam on the San Juan River in a way that reduces effects on the fish populations. The program is funded by a portion of revenues from hydropower revenues from WAPA in the Upper Basin, Reclamation, the Bureau of Indian Affairs, and participating states. Recovery efforts for listed fish are coordinated with the Upper Colorado Endangered Fish Recovery Program.~~New Mexico.~~
~~Congressional Research Service~~

13

~~Management of the Colorado River: Water Allocations, Drought, and the Federal Role~~

Glen Canyon Dam Adaptive Management Program
The Glen Canyon Dam Adaptive Management Program was established in 1997 in response to a directive The Glen Canyon Dam Adaptive Management Program was established in 1997 in response to a directive
from Congress under the Grand Canyon Protection Act of 1992 to operate Glen Canyon Dam “in such a from Congress under the Grand Canyon Protection Act of 1992 to operate Glen Canyon Dam “in such a
manner as to protect, mitigate adverse impacts to, and improve the values for which Grand Canyon manner as to protect, mitigate adverse impacts to, and improve the values for which Grand Canyon
National Park and Glen Canyon National Recreation Area were established.”National Park and Glen Canyon National Recreation Area were established.”7273 This program uses This program uses
experiments to determine how water flows affect natural resources south of the dam. Reclamation is in experiments to determine how water flows affect natural resources south of the dam. Reclamation is in
charge of modifying flows for experiments, and the U.S. Geological Survey conducts monitoring and charge of modifying flows for experiments, and the U.S. Geological Survey conducts monitoring and
other studies to evaluate the effects of the flows.other studies to evaluate the effects of the flows.7374 The results are expected to better inform managers how The results are expected to better inform managers how
to provide water deliveries and conserve species. to provide water deliveries and conserve species.
Lower Colorado Multi-Species Conservation Program
The Multi-Species Conservation Program (MSCP) is a multistakeholder initiative to conserve 27 species The Multi-Species Conservation Program (MSCP) is a multistakeholder initiative to conserve 27 species
(8 listed under ESA) along the Lower Colorado River while maintaining water and power supplies for (8 listed under ESA) along the Lower Colorado River while maintaining water and power supplies for
farmers, tribes, industries, and urban residents.farmers, tribes, industries, and urban residents.7475 The MSCP began in 2005 and is planned to last for at The MSCP began in 2005 and is planned to last for at
least 50 years.least 50 years.7576 The MSCP was created through consultation under ESA. To achieve compliance under The MSCP was created through consultation under ESA. To achieve compliance under
ESA, federal entities involved in managing water supplies in the Lower Colorado River Basin met with ESA, federal entities involved in managing water supplies in the Lower Colorado River Basin met with
resource agencies from Arizona, California, and Nevada; Native American Tribes; environmental groups; resource agencies from Arizona, California, and Nevada; Native American Tribes; environmental groups;
and recreation interests to develop a program to conserve species along a portion of the Colorado River. A and recreation interests to develop a program to conserve species along a portion of the Colorado River. A
biological opinion (BiOp) issued by the FWS in 1997 covers operations and maintenance activities biological opinion (BiOp) issued by the FWS in 1997 covers operations and maintenance activities
conducted by Reclamation along the Colorado River from Lake Mead to the Southerly International conducted by Reclamation along the Colorado River from Lake Mead to the Southerly International
~~Boundary; consultation was reinitiated in 2002, and a new BiOp was issued later that year.76 Nonfederal~~
~~stakeholders also applied and received an incidental take permit under Section 10(a) of the ESA for their~~
~~activities.77 This resulted in a habitat conservation plan for the MSCP that formed the basis for the~~
~~program.78 A Lower Colorado River Multi-Species Conservation Program Implementing Agreement~~
~~integrated the federal and nonfederal activities in the MSCP and was signed by stakeholders in 2005.79~~
~~The objective of the MSCP is to create habitat for listed species, augment the populations of species listed~~
~~under ESA, maintain current and future water diversions and power production, and abide by the~~
~~incidental take authorizations for listed species under the ESA. The estimated total cost of the program~~
~~over its lifetime is approximately $626 million in 2003 dollars ($903 million in 2019 dollars) and is to be~~
~~split evenly between Reclamation (50%) and the states of California, Nevada, and Arizona (who~~

72 71 For more information, see U.S. Fish and Wildlife Service, “San Juan River Basin Recovery Implementation Program,” at https://www.fws.gov/southwest/sjrip/. 72 It also includes participation by water development interests in Colorado and New Mexico. 73 For more information, see Reclamation, Glen Canyon Dam Adaptive Management Program, “Glen Canyon Dam High Flow For more information, see Reclamation, Glen Canyon Dam Adaptive Management Program, “Glen Canyon Dam High Flow
Experimental Release,” at https://www.usbr.gov/uc/progact/amp/ltemp.html. Experimental Release,” at https://www.usbr.gov/uc/progact/amp/ltemp.html.
7374 Regardless of the status and results of flow experiments, the total annual volume of water released from Glen Canyon Dam Regardless of the status and results of flow experiments, the total annual volume of water released from Glen Canyon Dam
remains dictated by the Law of the River, as described above. remains dictated by the Law of the River, as described above.
7475 The stakeholders include 6 federal and state agencies, 6 tribes, and 36 cities and water and power authorities. Stakeholders The stakeholders include 6 federal and state agencies, 6 tribes, and 36 cities and water and power authorities. Stakeholders
serve more than 20 million residents in the region, and irrigate 2 million acres of farmland. For more information, see Lower serve more than 20 million residents in the region, and irrigate 2 million acres of farmland. For more information, see Lower
Colorado River Multi-Species Conservation Program at https://www.lcrmscp.gov/. Colorado River Multi-Species Conservation Program at https://www.lcrmscp.gov/.
7576 The program was authorized under Subtitle E of Title IX of P.L. 111-11. The program was authorized under Subtitle E of Title IX of P.L. 111-11.
~~76 U.S. Fish and Wildlife Service, Reinitiation of Formal Section 7 Consultation on Lower Colorado River Operations and~~
~~Maintenance - Lake Mead to Southerly International Boundary, Arizona, California and Nevada, April 30, 2002,~~
~~https://www.usbr.gov/lc/region/g2000/BO2002operations.pdf.~~
~~77 The incidental take permit is valid for 50 years from its date of issuance and covers the implementation of the~~ Congressional Research Service 14 Management of the Colorado River: Water Allocations, Drought, and the Federal Role Boundary; consultation was reinitiated in 2002, and a new BiOp was issued later that year.77 Nonfederal stakeholders also applied and received an incidental take permit under Section 10(a) of the ESA for their activities.78 This resulted in a habitat conservation plan for the MSCP that formed the basis for the program.79 A Lower Colorado Lower Colorado
~~River Multi-Species Conservation Program, diversions of water from the river, demand for and receipt of hydropower, and flow~~
~~and non-flow actions along the Colorado River with the geographic scope of the permit.~~
~~78 Lower Colorado River Multi-Species Conservation Program,~~ ~~Final Lower Colorado River Multi-Species Conservation~~
~~Program Volume II: Habitat Conservation Plan, December 17, 2004, at https://lcrmscp.gov/lcrm-prod/lcrm-prod/pdfs/~~
~~hcp_volii_2004.pdf.~~
~~79 Lower Colorado River Multi-Species Conservation Program Implementing Agreement at https://lcrmscp.gov/lcrm-prod/lcrm-~~
~~prod/pdfs/imp_agr_2005.pdf.~~
~~Congressional Research Service~~

14

~~Management of the Colorado River: Water Allocations, Drought, and the Federal Role~~

River Multi-Species Conservation Program Implementing Agreement integrated the federal and nonfederal activities in the MSCP and was signed by stakeholders in 2005.80 The objective of the MSCP is to create habitat for listed species, augment the populations of species listed under ESA, maintain current and future water diversions and power production, and abide by the incidental take authorizations for listed species under the ESA. The estimated total cost of the program over its lifetime is approximately $626 million in 2003 dollars and is to be split evenly between Reclamation (50%) and the states of California, Nevada, and Arizona (who collectively fund the remaining 50%). The management and implementation of the MSCP is the collectively fund the remaining 50%). The management and implementation of the MSCP is the
responsibility of Reclamation, in consultation with a steering committee of stakeholders. responsibility of Reclamation, in consultation with a steering committee of stakeholders.
Hydropower Revenues Funding Colorado River Basin Activities
Hydropower revenues finance a number of activities throughout the Colorado River Basin. In the Lower Basin, the Hydropower revenues finance a number of activities throughout the Colorado River Basin. In the Lower Basin, the
Colorado River Dam Fund uses power revenues generated by the Boulder Canyon Project (i.e., Hoover Dam) to fund Colorado River Dam Fund uses power revenues generated by the Boulder Canyon Project (i.e., Hoover Dam) to fund
operational and construction costs for related Reclamation facilities. A separate fund, the Lower Colorado River Basin operational and construction costs for related Reclamation facilities. A separate fund, the Lower Colorado River Basin
Development Fund, Development Fund, ~~col ects~~collects revenues from the Central Arizona Project (CAP), as well as from a surcharge on revenues revenues from the Central Arizona Project (CAP), as well as from a surcharge on revenues
from the Boulder Canyon and Parker-Davis Projects that was enacted under the Hoover Power Plant Act of 1984 (P.L. 98-from the Boulder Canyon and Parker-Davis Projects that was enacted under the Hoover Power Plant Act of 1984 (P.L. 98-
381). These revenues are available without further appropriation toward defraying CAP operation and maintenance costs, 381). These revenues are available without further appropriation toward defraying CAP operation and maintenance costs,
salinity control efforts, and funding for Indian water rights settlements identified under the Arizona Water Settlements Act salinity control efforts, and funding for Indian water rights settlements identified under the Arizona Water Settlements Act
of 2004 (i.e., funding for water systems of the Gila River Indian Community and the Tohono O’odham Nation, among of 2004 (i.e., funding for water systems of the Gila River Indian Community and the Tohono O’odham Nation, among
others). In the Upper Basin, the Upper Colorado River Basin Fund others). In the Upper Basin, the Upper Colorado River Basin Fund ~~col ects~~collects revenues from the initial units of the Colorado revenues from the initial units of the Colorado
River Storage Project and funds operation and maintenance expenses, salinity control, the Glen Canyon Dam Adaptive River Storage Project and funds operation and maintenance expenses, salinity control, the Glen Canyon Dam Adaptive
Management Program, and endangered fish studies on the Colorado and San Juan rivers, among other things. Management Program, and endangered fish studies on the Colorado and San Juan rivers, among other things.
Source: Department of the Interior,Department of the Interior, Department of the Interior Budget Appendix, Fiscal Year 2023 Budget Request.
Tribal Water Rights
Tribal water rights are often senior to other uses on the Colorado River.Tribal water rights are often senior to other uses on the Colorado River.8081 Tribal water diversions based on Tribal water diversions based on
these rights typically come out of individual state allocations. There are 30 federally recognized tribes in these rights typically come out of individual state allocations. There are 30 federally recognized tribes in
the Colorado River Basin, many of whom have settled or unresolved (i.e., currently claimed for use but the Colorado River Basin, many of whom have settled or unresolved (i.e., currently claimed for use but
unsettled) tribal water rights.unsettled) tribal water rights.8182 As of early 2023, 11 basin tribes had reserved (i.e., held for future use) As of early 2023, 11 basin tribes had reserved (i.e., held for future use)
water rights claims that have not been quantified and settled; the total potential amount of these claims is water rights claims that have not been quantified and settled; the total potential amount of these claims is
~~unknown.82 According to Reclamation, as of December 2020, tribes held diversion rights to~~
~~approximately 3.4 MAF per year of Colorado River water.83 Previous studies noted that these tribes were~~
~~using just over half of their quantified rights.84~~
~~Because of the magnitude and seniority of tribal water rights, future decisions about the settlement and~~
~~development of tribal water rights in the~~ 77 U.S. Fish and Wildlife Service, Reinitiation of Formal Section 7 Consultation on Lower Colorado River Operations and Maintenance - Lake Mead to Southerly International Boundary, Arizona, California and Nevada, April 30, 2002, at https://www.usbr.gov/lc/region/g2000/BO2002operations.pdf. 78 The incidental take permit is valid for 50 years from its date of issuance and covers the implementation of the Lower Colorado Colorado River Multi-Species Conservation Program, diversions of water from the river, demand for and receipt of hydropower, and flow and non-flow actions along the Colorado River with the geographic scope of the permit. 79 Lower Colorado River Multi-Species Conservation Program, Final Lower Colorado River Multi-Species Conservation Program Volume II: Habitat Conservation Plan, December 17, 2004, at https://lcrmscp.gov/lcrm-prod/lcrm-prod/pdfs/hcp_volii_2004.pdf. 80 Lower Colorado River Multi-Species Conservation Program Implementing Agreement at https://lcrmscp.gov/lcrm-prod/lcrm-prod/pdfs/imp_agr_2005.pdf. 81~~River Basin are likely to influence the availability of~~
~~basin water resources for various uses. Increased consumptive water use by tribes with existing quantified~~
~~and settled water rights, and/or future settlement of claims and additional consumptive use of basin waters~~
~~by tribes with reserved rights, would exacerbate competition for basin water resources. At the same time,~~
~~some tribes have entered into arrangements to lease or conserve their waters to other users; new~~

80 Tribal water rights claims typically arise out of the right of many tribes to water resources dating to treaties establishing their Tribal water rights claims typically arise out of the right of many tribes to water resources dating to treaties establishing their
reservations. These water rights are often senior to those of non-Indian water rights holders because they date to the creation of reservations. These water rights are often senior to those of non-Indian water rights holders because they date to the creation of
the reservation (i.e., prior to the awarding of most state water rights). For more information on Indian water rights settlements, the reservation (i.e., prior to the awarding of most state water rights). For more information on Indian water rights settlements,
see CRS Report R44148, see CRS Report R44148, Indian Water Rights Settlements. .
8182 For a list of the tribes, see Bureau of Reclamation, “Colorado River Basin,” at https://www.usbr.gov/ColoradoRiverBasin/. Congressional Research Service 15 link to page 21 link to page 33 link to page 9 Management of the Colorado River: Water Allocations, Drought, and the Federal Role unknown.83 According to Reclamation, as of December 2020, tribes held diversion rights to approximately 3.4 MAF per year of Colorado River water.84 Previous studies noted that these tribes were using just over half of their quantified rights.85 Because of the magnitude and seniority of tribal water rights, future decisions about the settlement and development of tribal water rights in the Colorado River Basin are likely to influence the availability of basin water resources for various uses. Increased consumptive water use by tribes with existing quantified and settled water rights, and/or future settlement of claims and additional consumptive use of basin waters by tribes with reserved rights, would exacerbate competition for basin water resources. At the same time, some tribes have entered into arrangements to lease or conserve their waters to other users; new ~~For a list of the tribes, see Bureau of Reclamation, “Colorado River Basin,” at https://www.usbr.gov/ColoradoRiverBasin/.~~
~~82 CRS analysis of enacted Indian water rights settlements and Bureau of Reclamation,~~ ~~Colorado River Basin Water Supply and~~
~~Demand Study, Technical Report C- Water Demand Assessment, Appendix C9, Tribal Water Demand Scenario Quantification,~~
~~pp C9-33-C9-34. Tribes with claims yet to be fully adjudicated or quantified as of early 2023 include the Navajo Nation; the Ute~~
~~Indian Tribe of the Uintah and Ouray Reservation; the Havasupai Tribe; the Hopi Tribe; the Kaibab Band of Paiute Indians; the~~
~~Pascua Yaqui Tribe; San Carlos Apache Tribe; the San Juan Southern Paiute Tribe; the Tohono O’odham Nation; Tonto Apache~~
~~Tribe; and the Yavapai Apache Nation.~~
~~83 Reclamation,~~ ~~Review of the Colorado River Interim Guidelines for Lower Basin Shortages and Coordinated Operations for~~
~~Lake Powell and Lake Mead, December 2020, p. 14, at https://www.usbr.gov/ColoradoRiverBasin/documents/~~
~~7.D.Review_FinalReport_12-18-2020.pdf.~~
~~84 Colorado River Research Group, Tribes and Water in the Colorado River Basin, June 2016. According to this study, tribal~~
~~consumptive use in 2015 (including leasing of tribal water to non-tribal entities) totaled 1.7 MAF of the 2.9 MAF in recognized~~
~~diversion rights at that time.~~
~~Congressional Research Service~~

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~~link to page 21 link to page 22 link to page 22 link to page 35 link to page 9~~ ~~Management of the Colorado River: Water Allocations, Drought, and the Federal Role~~

agreements along these lines have the potential to secure water supplies for some non-tribal users without agreements along these lines have the potential to secure water supplies for some non-tribal users without
other viable alternative sources of water.other viable alternative sources of water.8586
Drought and the Supply/Demand Imbalance
The Colorado River Compact was based on the assumption (formed by the available record at the time) The Colorado River Compact was based on the assumption (formed by the available record at the time)
that average annual flows on the river were 16.4 MAF per year.that average annual flows on the river were 16.4 MAF per year.~~86 As noted, from 1906 to 2022, observed~~
~~historical natural flows on the river at Lee Ferry, AZ—the common point of measurement for observed~~
~~basin flows—averaged 14.6 MAF annually (Figure 3).87 Natural flows from 2000 to 2022 (i.e.,~~87 However, actual flows have been considerably less than that (and have dropped further during the during the
~~ongoing drought) averaged less than 12.1 MAF annually,88 with this period noted to be the driest 23-year~~
~~period on record.89 At the same time, consumptive use~~ongoing drought). In most years, consumptive uses and losses (e.g., evaporation) and losses (e.g., evaporation) ~~in the basin have~~
~~regularly exceeded natural flows (in particular during the current drought).90~~ of Colorado River waters exceed the river’s natural flows. This condition—referred to as the structural deficit—leads to a drawdown of basin reservoirs. Consumptive use in the basin Consumptive use in the basin
generally increased from 1971 to 2002 but declined after the 2003 approval of the Quantitative Settlement generally increased from 1971 to 2002 but declined after the 2003 approval of the Quantitative Settlement
Agreement (QSA), which Agreement (QSA), which ~~in part~~ led to a led to a marginal decrease of consumptive use in the Lower Basin (see below decrease of consumptive use in the Lower Basin (see below
section,section, “Recent Developments and Agreements”).88 In recent years, demand has dropped further, although the ongoing drought has continued to stress water supplies. In 2023, consumptive use in the Lower Basin is expected to be at its lowest level since 1984.89~~“Recent Developments and Agreements”).91 Despite this development, overall basin consumptive~~
~~use and other losses continue to exceed natural flows in most years; the resulting “structural deficit” has~~
~~caused a drawdown of basin storage (Figure 4)~~.
The lack of a formal mechanism accounting for evaporative losses in the Lower Basin exacerbates the The lack of a formal mechanism accounting for evaporative losses in the Lower Basin exacerbates the
supply/demand disparity. A key difference between Upper and Lower Basin reporting involves how each supply/demand disparity. A key difference between Upper and Lower Basin reporting involves how each
basin accounts for consumptive use. In accordance with Articles I and V of the basin accounts for consumptive use. In accordance with Articles I and V of the Arizona v. California
decree,decree,9290 a Lower Basin Water Accounting Report (published annually) reports only on diversions from 83 CRS analysis of enacted Indian water rights settlements and Bureau of Reclamation, Colorado River Basin Water Supply and Demand Study, Technical Report C- Water Demand Assessment, Appendix C9, Tribal Water Demand Scenario Quantification, pp. C9-33–C9-34. Tribes with claims yet to be fully adjudicated or quantified as of early 2023 include the Navajo Nation; the Ute Indian Tribe of the Uintah and Ouray Reservation; the Havasupai Tribe; the Hopi Tribe; the Kaibab Band of Paiute Indians; the Pascua Yaqui Tribe; San Carlos Apache Tribe; the San Juan Southern Paiute Tribe; the Tohono O’odham Nation; Tonto Apache Tribe; and the Yavapai Apache Nation. 84 Reclamation, Review of the Colorado River Interim Guidelines for Lower Basin Shortages and Coordinated Operations for Lake Powell and Lake Mead, December 2020, p. 14, at https://www.usbr.gov/ColoradoRiverBasin/documents/7d/7.D.Review_FinalReport_12-18-2020.pdf. 85 Colorado River Research Group, Tribes and Water in the Colorado River Basin, June 2016. According to this study, tribal consumptive use in 2015 (including leasing of tribal water to non-tribal entities) totaled 1.7 MAF of the 2.9 MAF in recognized diversion rights at that time. 86 See footnote 143. 87 National Research Council, Committee on the Scientific Bases of Colorado River Basin Water Management, Water Science and Technology Board, Colorado River Basin Water Management: Evaluating and Adjusting to Hydroclimatic Variability, 2007, at https://www.nap.edu/read/11857/chapter/1. 88 ~~a Lower Basin Water Accounting Report (published annually) reports only on~~ ~~diversions from~~
~~the system for consumptive use. Conversely, the comparable Upper Basin accounting—the Upper Basin~~
~~Consumptive Use and Losses Report (published every five years)—is prepared in response to~~
~~congressional direction in the CRBPA, which directed “a detailed breakdown of the beneficial~~
~~consumptive use of water on a State-by-State basis.93 Reclamation defines beneficial consumptive use to~~
~~include any removal from the system for beneficial consumptive use, which Reclamation defines to~~
~~include both diversions and losses from mainstem reservoir evaporation that occur prior to diversions 94~~
~~Thus, even though Lower Basin consumptive use is typically below the compact threshold of 7.5 MAF,~~
~~after accounting for evaporative losses, the total amount of water regularly exceeds this thresholds.~~

~~85 See footnote 142.~~
~~86 National Research Council, Committee on the Scientific Bases of Colorado River Basin Water Management, Water Science~~
~~and Technology Board, Colorado River Basin Water Management: Evaluating and Adjusting to Hydroclimatic Variability, 2007,~~
~~at https://www.nap.edu/read/11857/chapter/1.~~
~~87 Reclamation, “Reclamation Flow Data.”~~
~~88 Ibid.~~
~~89 87 FR 37884, 2022.~~
~~90 Consumptive uses and losses include reservoir evaporation and other consumptive use losses, which average an estimated 2~~
~~MAF per year. For more information on consumptive use, see Reclamation Consumptive Uses and Losses Reports at~~
~~https://www.usbr.gov/uc/DocLibrary/reports.html and Reclamation Colorado River Water Accounting and Use Reports at~~
~~https://www.usbr.gov/lc/region/g4000/wtracct.html.~~
91 Consumptive use in the Lower Basin (excluding tributaries and evaporative losses) was in excess of 8.4 MAF in 2002 but had Consumptive use in the Lower Basin (excluding tributaries and evaporative losses) was in excess of 8.4 MAF in 2002 but had
decreased to 6.8 MAF as of 2020. decreased to 6.8 MAF as of 2020.
~~92 See footnote 25.~~
~~93 43 U.S.C. §1551.~~
~~94 See Bureau of Reclamation, Upper Colorado River Basin Consumptive Uses and Losses Report, 2016-2020, February 2022, p.~~
6.
~~Congressional Research Service~~

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89 Arizona Department of Water Resources, “Arizona, California and Nevada commit to record-setting conservation to protect the Colorado River,” press release, October 19, 2023, at https://azwaternews.com/2023/10/19/arizona-california-and-nevada-commit-to-record-setting-conservationto-protect-the-colorado-river/. 90 See footnote 25. Congressional Research Service 16 Management of the Colorado River: Water Allocations, Drought, and the Federal Role the system for consumptive use. Conversely, the comparable Upper Basin accounting—the Upper Basin Consumptive Use and Losses Report (published every five years)—is prepared in response to congressional direction in the CRBPA, which directed “a detailed breakdown of the beneficial consumptive use of water on a State-by-State basis.”91 Reclamation defines beneficial consumptive use to include any removal from the system for beneficial consumptive use, which Reclamation defines to include both diversions and losses from mainstem reservoir evaporation that occur prior to diversions 92 Thus, even though Lower Basin consumptive use is typically below the compact threshold of 7.5 MAF, after accounting for evaporative losses, the total amount of water regularly exceeds this threshold. Studies~~Management of the Colorado River: Water Allocations, Drought, and the Federal Role~~

~~Figure 3. Colorado River Natural Flow at Lees Ferry, Arizona,~~
~~with 10-Year Moving Average, 1906-2022~~

Source: Bureau of Reclamation data, General Modeling Information, at https://www.usbr.gov/lc/region/g4000/riverops/
~~model-info.html.~~
~~Congressional Research Service~~

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~~Management of the Colorado River: Water Allocations, Drought, and the Federal Role~~

~~Figure 4. Combined Storage at Lakes Mead and Powell, 1960-2022~~

Source: Bureau of Reclamation, “Notice of Intent to Prepare a Supplemental Environmental Impact Statement,” Public
~~Webinar, November 9, 2022.~~
Note: Total storage = 52.3 mil ion acre-feet.
~~Recent studies~~ have concluded that Colorado River flows are unlikely to return to 20th century averages have concluded that Colorado River flows are unlikely to return to 20th century averages
and that future water supply risk is high.and that future water supply risk is high.9593 Overall, natural flows have declined by approximately 20% Overall, natural flows have declined by approximately 20%
over the last century, and one study attributed more than half of this decline to increasing temperatures over the last century, and one study attributed more than half of this decline to increasing temperatures
resulting from climate change.resulting from climate change.9694 Although there is potential for some precipitation increases in the region Although there is potential for some precipitation increases in the region
due to climate change, such potential increases are not expected to counteract projected drying resulting due to climate change, such potential increases are not expected to counteract projected drying resulting
from rising temperatures.from rising temperatures.9795 As a result, most research has projected continuing reduction in runoff through As a result, most research has projected continuing reduction in runoff through
the mid-21st century.the mid-21st century.9896
Recent Developments and Agreements
Drought conditions throughout the basin have raised concerns about potential negative impacts on water Drought conditions throughout the basin have raised concerns about potential negative impacts on water
supplies. Concerns center on what sort of changes to the current water management regime might result if supplies. Concerns center on what sort of changes to the current water management regime might result if

~~95 B. Udall and J. Overpeck, “The Twenty-First Century Colorado River Hot Drought and Implications for the Future,”~~ ~~Water~~
~~Resources Research, vol. 53 (February 17, 2017), pp. 2404-2418.~~
~~96 Paul C. D. Milly and Krista A. Dunne, “Colorado River Flow Dwindles as Warming-Driven Loss of Reflective Snow~~
~~Energizes Evaporation,” Science, vol. 367, no. 6483 (March 13, 2020), pp. 1252-1255. Hereinafter, Milly and Dunne, “Colorado~~
~~River Flow Dwindles.” Also see Mu Xiao, Bradley Udall, and Dennis P. Lettenmaier, “On the Causes of Declining Colorado~~
~~River Streamflows,” Water Resources Research 54 (2018), pp. 6739–6756.~~
~~97 Milly and Dunne, “Colorado River Flow Dwindles.”~~
~~98 Jeff Lukas and Elizabeth Payton, eds., Colorado River Basin Climate and Hydrology: State of the Science, Western Water~~
~~Assessment, University of Colorado Boulder, 2020.~~
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~~Management of the Colorado River: Water Allocations, Drought, and the Federal Role~~

the Secretary of the Interior were to determine that a shortage condition exists in the Lower Basin. Some the Secretary of the Interior were to determine that a shortage condition exists in the Lower Basin. Some
in Upper Basin States are also concerned about the potential for a in Upper Basin States are also concerned about the potential for a compact call of Lower Basin states on of Lower Basin states on
Upper Basin states. This is the commonly used term for the Lower Basin states’ hypothetical attempt to Upper Basin states. This is the commonly used term for the Lower Basin states’ hypothetical attempt to
force deliveries of Colorado River water under the compact.force deliveries of Colorado River water under the compact.9997
Drought and other uncertainties related to water rights priorities (e.g., potential tribal water rights claims) Drought and other uncertainties related to water rights priorities (e.g., potential tribal water rights claims)
spurred the development of several efforts that generally attempted to relieve pressure on basin water spurred the development of several efforts that generally attempted to relieve pressure on basin water
supplies, stabilize storage levels, and provide assurances of available water supplies. Some of the most supplies, stabilize storage levels, and provide assurances of available water supplies. Some of the most
prominent developments since the year 2000 (i.e., the beginning of the current drought) are discussed prominent developments since the year 2000 (i.e., the beginning of the current drought) are discussed
below. below.
2003 Quantitative Settlement Agreement
Prior to the 2003 finalization of the QSA, California had been using approximately 5.2 MAF of Colorado Prior to the 2003 finalization of the QSA, California had been using approximately 5.2 MAF of Colorado
River on average each year (with most of its excess water use attributed to urban areas). Under the QSA, River on average each year (with most of its excess water use attributed to urban areas). Under the QSA,
which is an agreement between several California water districts and DOI, California agreed to reduce its which is an agreement between several California water districts and DOI, California agreed to reduce its
91 43 U.S.C. §1551. 92 See Bureau of Reclamation, Upper Colorado River Basin Consumptive Uses and Losses Report, 2016-2020, February 2022, p. 6. 93 B. Udall and J. Overpeck, “The Twenty-First Century Colorado River Hot Drought and Implications for the Future,” Water Resources Research, vol. 53 (February 17, 2017), pp. 2404-2418. 94 Paul C. D. Milly and Krista A. Dunne, “Colorado River Flow Dwindles as Warming-Driven Loss of Reflective Snow Energizes Evaporation,” Science, vol. 367, no. 6483 (March 13, 2020), pp. 1252-1255. Hereinafter, Milly and Dunne, “Colorado River Flow Dwindles.” Also see Mu Xiao, Bradley Udall, and Dennis P. Lettenmaier, “On the Causes of Declining Colorado River Streamflows,” Water Resources Research 54 (2018), pp. 6739-6756. 95 Milly and Dunne, “Colorado River Flow Dwindles.” 96 Jeff Lukas and Elizabeth Payton, eds., Colorado River Basin Climate and Hydrology: State of the Science, Western Water Assessment, University of Colorado Boulder, 2020. 97 For more background, see Anne Castle and John Fleck, “The Risk of Curtailment under the Colorado River Compact,” November 20, 2019, at https://ssrn.com/abstract=3483654. Congressional Research Service 17 Management of the Colorado River: Water Allocations, Drought, and the Federal Role use to the required 4.4 MAF under the Law of the River.98~~use to the required 4.4 MAF under the Law of the River.100~~ It sought to accomplish this aim by It sought to accomplish this aim by
quantifying Colorado River entitlement levels of several water contractors; authorizing efforts to conserve quantifying Colorado River entitlement levels of several water contractors; authorizing efforts to conserve
additional water supplies (e.g., the lining of the All-American Canal); and providing for several large-additional water supplies (e.g., the lining of the All-American Canal); and providing for several large-
scale, long-term agriculture-to-urban water transfers. The QSA also committed the state to a path toward scale, long-term agriculture-to-urban water transfers. The QSA also committed the state to a path toward
restoration and mitigation related to the Salton Sea in Southern California.restoration and mitigation related to the Salton Sea in Southern California.~~101~~99
A related agreement between Reclamation and the Lower Basin states, the Inadvertent Overrun and A related agreement between Reclamation and the Lower Basin states, the Inadvertent Overrun and
Payback Policy (IOPP), went into effect concurrently with the QSA in 2004.Payback Policy (IOPP), went into effect concurrently with the QSA in 2004.~~102~~100 IOPP is an administrative IOPP is an administrative
mechanism that provides an accounting of inadvertent overruns in consumptive use compared to the mechanism that provides an accounting of inadvertent overruns in consumptive use compared to the
annual entitlements of water users in the Lower Basin. These overruns must be “paid back” in the annual entitlements of water users in the Lower Basin. These overruns must be “paid back” in the
calendar year following the overruns, and the paybacks must be made only from “extraordinary calendar year following the overruns, and the paybacks must be made only from “extraordinary
conservation measures” above and beyond normal consumptive use.conservation measures” above and beyond normal consumptive use.~~103~~101
2004 Arizona Water Settlements Act
The 2004 Arizona Water Settlements Act (AWSA,) altered the allocation of CAP water in Arizona. It The 2004 Arizona Water Settlements Act (AWSA,) altered the allocation of CAP water in Arizona. It
ratified three water rights settlements (one in each title) between the federal government and the State of ratified three water rights settlements (one in each title) between the federal government and the State of
Arizona, the Gila River Indian Community (GRIC), and the Tohono O’odham Nation, respectively.Arizona, the Gila River Indian Community (GRIC), and the Tohono O’odham Nation, respectively.~~104~~102 For For
the state and its CAP water users, the settlement resolved a final repayment cost for CAP by reducing the the state and its CAP water users, the settlement resolved a final repayment cost for CAP by reducing the
water users’ reimbursable repayment obligation from about $2.3 billion to $1.7 billion. Additionally, water users’ reimbursable repayment obligation from about $2.3 billion to $1.7 billion. Additionally,
Arizona agreed to new tribal and non-tribal allocations of CAP water so that approximately half of CAP’s Arizona agreed to new tribal and non-tribal allocations of CAP water so that approximately half of CAP’s

~~99 For more background, see Anne Castle and John Fleck, “The Risk of Curtailment under the Colorado River Compact,”~~
~~November 20, 2019, at https://ssrn.com/abstract=3483654.~~
~~100~~annual allotment would be available to Native American tribes in Arizona, at a higher priority than most other uses. The tribal communities were authorized to lease the water, so long as the water remains within the state via the state’s water banking authority. The act authorized funds to cover the cost of infrastructure required to deliver the water to the Indian communities, much of it derived from power receipts accruing to the Lower Colorado River Basin Development Fund. It also authorized funding for the study of a potential New Mexico Unit of CAP. 2007 Interim Guidelines/Coordinated Operations for Lake Powell and Lake Mead Another development in the basin wasp the 2007 adoption of the Colorado River Interim Guidelines for Lower Basin Shortages and the Coordinated Operations for Lake Powell and Lake Mead (2007 Interim Guidelines). DOI developed the guidelines to implement the LROC, through issuance of the Annual Operating Plan for Colorado River Reservoirs (AOP), as directed by the 1968 CRBPA.103 Development 98 California Quantification Settlement Agreement by and Among Imperial Irrigation District, the Metropolitan Water District of California Quantification Settlement Agreement by and Among Imperial Irrigation District, the Metropolitan Water District of
Southern California, and Coachella Valley Water District, October 10, 2003. Southern California, and Coachella Valley Water District, October 10, 2003.
~~101~~99 The Salton Sea is an inland water body in Southern California that was historically sustained by Colorado River irrigation The Salton Sea is an inland water body in Southern California that was historically sustained by Colorado River irrigation
runoff from the Imperial and Coachella Valleys, but is shrinking. Toxic dust from exposed seabed is a major concern for runoff from the Imperial and Coachella Valleys, but is shrinking. Toxic dust from exposed seabed is a major concern for
surrounding areas. For more information on the Salton Sea, see CRS Report R46625, surrounding areas. For more information on the Salton Sea, see CRS Report R46625, Salton Sea Restoration. .
~~102~~100 Reclamation, Reclamation, Record of Decision for the Colorado River Water Delivery Agreement, October 10, 2003, pp. 16-19., October 10, 2003, pp. 16-19.
~~103~~101 Ibid. Ibid.
~~104~~102 Congress passed the Colorado River Basin Project Act of 1968 and authorized construction of CAP despite significant Congress passed the Colorado River Basin Project Act of 1968 and authorized construction of CAP despite significant
uncertainty related to tribal water rights related to the Colorado River. The Gila River, Arizona’s largest tributary of the Colorado uncertainty related to tribal water rights related to the Colorado River. The Gila River, Arizona’s largest tributary of the Colorado
River, runs directly through the Gila River Indian Community, which encompasses approximately 372,000 acres south of and River, runs directly through the Gila River Indian Community, which encompasses approximately 372,000 acres south of and
adjacent to Phoenix. Additionally, the Tohono O’odham Nation possessed reserved water rights near Tucson with the potential to adjacent to Phoenix. Additionally, the Tohono O’odham Nation possessed reserved water rights near Tucson with the potential to
disrupt that city’s water supplies. disrupt that city’s water supplies.
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~~annual allotment would be available to Native American tribes in Arizona, at a higher priority than most~~
~~other uses. The tribal communities were authorized to lease the water, so long as the water remains within~~
~~the state via the state’s water banking authority. The act authorized funds to cover the cost of~~
~~infrastructure required to deliver the water to the Indian communities, much of it derived from power~~
~~receipts accruing to the Lower Colorado River Basin Development Fund. It also authorized funding for~~
~~the study of a potential New Mexico Unit of CAP.~~
~~2007 Interim Guidelines/Coordinated Operations for Lake Powell and~~
~~Lake Mead~~
~~Another development in the basin was the 2007 adoption of the~~103 Secretary of the Interior, Record of Decision: Colorado River Interim Guidelines for Colorado River Interim Guidelines for
Lower Basin Shortages and the Coordinated Operations for Lake Powell and Lake Mead (Lower Basin Shortages and the Coordinated Operations for Lake Powell and Lake Mead (~~2007 Interim~~
~~Guidelines). DOI developed the guidelines to implement the LROC, through issuance of the~~ ~~Annual~~
~~Operating Plan for Colorado River Reservoirs~~ ~~(AOP), as directed by the 1968 CRBPA.105 Development~~
December 2007), p. 4, at https://www.usbr.gov/lc/region/programs/strategies/RecordofDecision.pdf. Congressional Research Service 18 link to page 24 Management of the Colorado River: Water Allocations, Drought, and the Federal Role of the agreement began in 2005, when, in response to drought in the Southwest and the decline in basin of the agreement began in 2005, when, in response to drought in the Southwest and the decline in basin
water storage, the Secretary of the Interior instructed Reclamation to develop coordinated strategies for water storage, the Secretary of the Interior instructed Reclamation to develop coordinated strategies for
Colorado River reservoir operations during drought or shortages.Colorado River reservoir operations during drought or shortages.~~106~~104 The resulting guidelines included The resulting guidelines included
criteria for releases from Lakes Mead and Powell determined by “trigger levels” in both reservoirs, as criteria for releases from Lakes Mead and Powell determined by “trigger levels” in both reservoirs, as
well as a schedule of Lower Basin curtailments at different operational tierswell as a schedule of Lower Basin curtailments at different operational tiers ~~(Table 1). Under the~~
~~guidelines,~~. For Lake Powell, preset inflow measurements determine the reservoir’s annual operational “balancing” tier and resulting releases to Lake Mead. In the Lower Basin, the guidelines stipulated that Arizona and Nevada, which have junior rights to California, Arizona and Nevada, which have junior rights to California, ~~would face~~receive reduced allocations if reduced allocations if
Lake Mead elevations dropped below 1,075 feet. At the time, it was thought that the 2007 Guidelines Lake Mead elevations dropped below 1,075 feet. At the time, it was thought that the 2007 Guidelines
would significantly reduce the risk of Lake Mead falling to would significantly reduce the risk of Lake Mead falling to an elevation of 1,025 feet. 1,025 feet.
The 2007 agreement also included for the first time a mechanism by which parties in the Lower Basin The 2007 agreement also included for the first time a mechanism by which parties in the Lower Basin
were able to store conserved water in Lake Mead, known as Intentionally Created Surplus (ICS). were able to store conserved water in Lake Mead, known as Intentionally Created Surplus (ICS).
Reclamation accounts for this water annually, and the users storing the water may access the surplus in Reclamation accounts for this water annually, and the users storing the water may access the surplus in
future years, in accordance with the Law of the River. As of 2020, the portion of Lake Mead water in future years, in accordance with the Law of the River. As of 2020, the portion of Lake Mead water in
storage that was classified as ICS was 2.99 MAF.storage that was classified as ICS was 2.99 MAF.~~107~~105 That is, as of the end of the 2021 water year, That is, as of the end of the 2021 water year,
approximately one-third of the water stored in Lake Mead was previously conserved ICS volume. approximately one-third of the water stored in Lake Mead was previously conserved ICS volume.
The 2007 guidelines are considered “interim” because they are scheduled to expire in 20 years (i.e., at the The 2007 guidelines are considered “interim” because they are scheduled to expire in 20 years (i.e., at the
end of 2026). Thus, Reclamation began coordinating a review on the effectiveness of the 2007 guidelines end of 2026). Thus, Reclamation began coordinating a review on the effectiveness of the 2007 guidelines
in 2020, and in 2022 formally initiated the review process for post-2026 operations.in 2020, and in 2022 formally initiated the review process for post-2026 operations.~~108~~106 The review is The review is
expected to encompass negotiations related to renewal of the Upper and Lower Basin DCPs, which are an expected to encompass negotiations related to renewal of the Upper and Lower Basin DCPs, which are an
overlay on the 2007 guidelines (see below overlay on the 2007 guidelines (see below ~~section,~~section, “2019 Drought Contingency Plans”).).
System Conservation Program
In 2014, Reclamation and several major basin water supply agencies (Central Arizona Water In 2014, Reclamation and several major basin water supply agencies (Central Arizona Water
Conservation District, Southern Nevada Water Authority, Metropolitan Water District of Southern Conservation District, Southern Nevada Water Authority, Metropolitan Water District of Southern

~~105 Secretary of the Interior, Record of Decision: Colorado River Interim Guidelines for Lower Basin Shortages and the~~
~~Coordinated Operations for Lake Powell and Lake Mead (December 2007), p. 4, at https://www.usbr.gov/lc/region/programs/~~
~~strategies/RecordofDecision.pdf.~~
~~106~~California, and Denver Water) executed a memorandum of understanding to provide funding for voluntary conservation projects and reductions of water use. The activities outlined in the memorandum had the goal of developing new system water,107 to be applied toward storage in Lake Mead, by the end of 2019.108 Congress formally authorized federal participation in these efforts, known as the Pilot System Conservation Program, in the Energy and Water Development and Related Agencies Appropriations Act, 2015 (P.L. 113-235, Division D). The Energy and Water Development and Related Agencies Appropriations Act, 2019 (P.L. 115-244, Division A) extended the authority through the end of FY2022, with the stipulation that Upper Basin agreements could not proceed without the participation of the Upper Basin states through the Upper Colorado River Commission. The authority was most recently extended 104 Prior to this time, the Secretary of the Interior had the authority to declare a shortage, but no shortage criteria had been Prior to this time, the Secretary of the Interior had the authority to declare a shortage, but no shortage criteria had been
publicly announced or published. (Criteria for surplus operations were put in place in 2001.) publicly announced or published. (Criteria for surplus operations were put in place in 2001.)
~~107~~105 Bureau of Reclamation, Bureau of Reclamation, Colorado River Accounting and Water Use Report, Calendar Year 2021, at https://www.usbr.gov/lc/, at https://www.usbr.gov/lc/
region/g4000/wtracct.html. region/g4000/wtracct.html.
~~108~~106 Department of the Interior, Reclamation, “Request for Input on Development of Post-2026 Colorado River Reservoir Department of the Interior, Reclamation, “Request for Input on Development of Post-2026 Colorado River Reservoir
Operational Strategies for Lake Powell and Lake Mead Under Historically Low Reservoir Conditions,” 87Operational Strategies for Lake Powell and Lake Mead Under Historically Low Reservoir Conditions,” 87 Federal Register
37884-37888, June 24, 2022. 37884-37888, June 24, 2022.
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~~California, and Denver Water) executed a memorandum of understanding to provide funding for~~
~~voluntary conservation projects and reductions of water use. The activities outlined in the memorandum~~
~~had the goal of developing new system water,109 to be applied toward storage in Lake Mead, by the end of~~
~~2019.110 Congress formally authorized federal participation in these efforts, known as the Pilot System~~
~~Conservation Program, in the Energy and Water Development and Related Agencies Appropriations Act,~~
~~2015 (P.L. 113-235, Division D). The Energy and Water Development and Related Agencies~~
~~Appropriations Act, 2019 (P.L. 115-244, Division A) extended the authority through the end of FY2022,~~
~~with the stipulation that Upper Basin agreements could not proceed without the participation of the Upper~~
~~Basin states through the Upper Colorado River Commission. The authority was most recently extended~~
107 System water refers to water that is provided to increase water supplies as a whole, without being directed toward additional consumptive use for specific contractors or water users. 108 Agreement Among the United States of America, Through the Department of the Interior, Bureau of Reclamation, the Central Arizona Water Conservation District, the Metropolitan Water District of Southern California, Denver Water, and the Southern Nevada Water Authority, for a Pilot Program for Funding the Creation of Colorado River System Water Through Voluntary Water Conservation and Reductions in Use, Agreement No. 14-XX-30-W0574, July 30, 2014, at https://www.usbr.gov/lc/region/programs/PilotSysConsProg/PilotSCPFundingAgreement7-30-2014.pdf. Congressional Research Service 19 link to page 24 Management of the Colorado River: Water Allocations, Drought, and the Federal Role through FY2024 in Division CC of the Consolidated Appropriations Act, FY2023 (P.L. 117-328). through FY2024 in Division CC of the Consolidated Appropriations Act, FY2023 (P.L. 117-328).
Reclamation estimated that as of the end of 2019, the Lower Basin program had conserved more than Reclamation estimated that as of the end of 2019, the Lower Basin program had conserved more than
175,000 AF of water in Lake Mead, at an average cost of $170 per AF.175,000 AF of water in Lake Mead, at an average cost of $170 per AF.~~111~~109 Additional projects also were Additional projects also were
carried out in the Upper Basin by the Upper Colorado River Basin Commission; these efforts ended in carried out in the Upper Basin by the Upper Colorado River Basin Commission; these efforts ended in
2018.2018.~~112~~110
Minute 319 and Minute 323 Agreements with ~~Mexico113~~Mexico111
In 2017, the United States and Mexico signed Minute 323, which extended and replaced elements of a In 2017, the United States and Mexico signed Minute 323, which extended and replaced elements of a
previous agreement related to implementation of the 1944 U.S.-Mexico Water Treaty, Minute 319, signed previous agreement related to implementation of the 1944 U.S.-Mexico Water Treaty, Minute 319, signed
in 2012.in 2012.~~114~~112 Minute 323 includes, among other things, options for Mexico to hold water in reserve in U.S. Minute 323 includes, among other things, options for Mexico to hold water in reserve in U.S.
reservoirs for emergencies and water conservation efforts, as well as U.S. commitments for flows to reservoirs for emergencies and water conservation efforts, as well as U.S. commitments for flows to
support the ecological health of the Colorado River Delta. It also extended the initial Mexican cutback support the ecological health of the Colorado River Delta. It also extended the initial Mexican cutback
commitments made under Minute 319 (which were similar in structure to the 2007 cutbacks negotiated commitments made under Minute 319 (which were similar in structure to the 2007 cutbacks negotiated
for Lower Basin states) and established a Binational Water Scarcity Contingency Plan that included for Lower Basin states) and established a Binational Water Scarcity Contingency Plan that included
additional cutbacks that would be triggered if DCPs are approved by U.S. basin states (see the following additional cutbacks that would be triggered if DCPs are approved by U.S. basin states (see the following
section,section, “2019 Drought Contingency Plans”).).
2019 Drought Contingency Plans
Ongoing drought conditions and the potential for water supply shortages prompted discussions and Ongoing drought conditions and the potential for water supply shortages prompted discussions and
negotiations focused on how to conserve additional basin water supplies. After several years of negotiations focused on how to conserve additional basin water supplies. After several years of
negotiations, on March 19, 2019, Reclamation and the Colorado River Basin states finalized DCPs for negotiations, on March 19, 2019, Reclamation and the Colorado River Basin states finalized DCPs for
both the Upper Basin and the Lower Basin. These plans, which are an overlay of the 2007 Interim both the Upper Basin and the Lower Basin. These plans, which are an overlay of the 2007 Interim
Guidelines discussed above, required final authorization by Congress to be implemented. Congress Guidelines discussed above, required final authorization by Congress to be implemented. Congress
approved the plans on April 16, 2019, in the Colorado River Drought Contingency Plan Authorization approved the plans on April 16, 2019, in the Colorado River Drought Contingency Plan Authorization

~~109 System water refers to water that is provided to increase water supplies as a whole, without being directed toward additional~~
~~consumptive use for specific contractors or water users.~~
~~110 Agreement Among the United States of America, Through the Department of the Interior, Bureau of Reclamation, the Central~~
~~Arizona Water Conservation District, the Metropolitan Water District of Southern California, Denver Water, and the Southern~~
~~Nevada Water Authority, for a Pilot Program for Funding the Creation of Colorado River System Water Through Voluntary~~
~~Water Conservation and Reductions in Use, Agreement No. 14-XX-30-W0574, July 30, 2014, at https://www.usbr.gov/lc/region/~~
~~programs/PilotSysConsProg/PilotSCPFundingAgreement7-30-2014.pdf.~~
~~111~~Act; like the 2007 guidelines, these plans are scheduled to be in place through 2026. At the time of their enactment, the combined efforts represented by the DCPs were expected to cut the risk of Colorado River reservoirs reaching critically low elevations by approximately 50%.113 Each of the basin-level DCPs is discussed below in more detail. Upper Basin Drought Contingency Plan The Upper Basin DCP aims to protect against Lake Powell reaching critically low elevations through coordinated Upper Basin reservoir operations. It also authorizes storage of conserved water in the Upper Basin that would serve as the foundation for a water use reduction effort (i.e., a Demand Management Program) that may be developed in the future.114 109 For individual projects, see Lower Colorado Region, “Pilot System Conservation Program,” at https://www.usbr.gov/lc/region/programs/ Lower Colorado Region, “Pilot System Conservation Program,” at https://www.usbr.gov/lc/region/programs/
PilotSysConsProg/pilotsystem.html. Accessed PilotSysConsProg/pilotsystem.html. Accessed ~~January 17~~October 30, 2023. , 2023.
~~112~~110 For more information, see Upper Colorado River Commission, “System Conservation Pilot Program,” at For more information, see Upper Colorado River Commission, “System Conservation Pilot Program,” at
http://www.ucrcommission.com/system-conservation-pilot-program/. http://www.ucrcommission.com/system-conservation-pilot-program/.
~~113~~111 For more information on the 1994 U.S.-Mexico Water Treaty and Colorado River water sharing issues with Mexico, see CRS For more information on the 1994 U.S.-Mexico Water Treaty and Colorado River water sharing issues with Mexico, see CRS
Report R45430, Report R45430, Sharing the Colorado River and the Rio Grande: Cooperation and Conflict with Mexico, by Nicole T. Carter, , by Nicole T. Carter,
Stephen P. Mulligan, and Charles V. Stern. Stephen P. Mulligan, and Charles V. Stern.
~~114~~112 International Boundary & Water Commission, “Minutes between the United States and Mexican Sections of the IBWC,” at International Boundary & Water Commission, “Minutes between the United States and Mexican Sections of the IBWC,” at
https://www.ibwc.gov/Treaties_Minutes/Minutes.html. https://www.ibwc.gov/Treaties_Minutes/Minutes.html.
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~~Act; like the 2007 guidelines, these plans are scheduled to be in place through 2026. At the time of their~~
~~enactment, the combined efforts represented by the DCPs were expected to cut the risk of Colorado River~~
~~reservoirs reaching critically low elevations by approximately 50%.115 Each of the basin-level DCPs is~~
~~discussed below in more detail.~~
~~Upper Basin Drought Contingency Plan~~
~~The Upper Basin DCP aims to protect against Lake Powell reaching critically low elevations through~~
~~coordinated Upper Basin reservoir operations. It also authorizes storage of conserved water in the Upper~~
~~Basin that would serve as the foundation for a water use reduction effort (i.e., a~~ ~~Demand Management~~
~~Program) that may be developed in the future.116~~
113 U.S. Congress, House Committee on Natural Resources, Subcommittee on Water, Oceans, and Wildlife, Oversight Hearing on the Colorado River Drought Contingency Plan, 116th Cong., 1st sess., March 28, 2019, H.Hrg. 116-10 (Washington: GPO, 2019). Hereinafter, 2019 House Natural Resources DCP Hearing. 114 While such a mechanism exists for the Lower Basin, a comparable program has not been developed in the Upper Basin. Congressional Research Service 20 link to page 26 Management of the Colorado River: Water Allocations, Drought, and the Federal Role Under the Upper Basin DCP’s Drought Response Operations Agreement (DROA), the Upper Basin states Under the Upper Basin DCP’s Drought Response Operations Agreement (DROA), the Upper Basin states
agree to operate system units to keep the surface of Lake Powell above 3,525 feet, which is 35 feet above agree to operate system units to keep the surface of Lake Powell above 3,525 feet, which is 35 feet above
“minimum power pool” (i.e., 3,490 feet, the minimum elevation needed to run the dam’s hydroelectric “minimum power pool” (i.e., 3,490 feet, the minimum elevation needed to run the dam’s hydroelectric
plant). Under DROA, the two main mechanisms to do this are altering the timing of releases from Glen plant). Under DROA, the two main mechanisms to do this are altering the timing of releases from Glen
Canyon Dam and operating “initial unit” reservoirs on the mainstem of the Colorado River (e.g., Navajo Canyon Dam and operating “initial unit” reservoirs on the mainstem of the Colorado River (e.g., Navajo
Reservoir, Blue Mesa Reservoir, and Flaming Gorge Reservoir) to protect Lake Powell elevations, Reservoir, Blue Mesa Reservoir, and Flaming Gorge Reservoir) to protect Lake Powell elevations,
potentially through storage drawdown. Operational changes may occur either through DROA’s emergency potentially through storage drawdown. Operational changes may occur either through DROA’s emergency
provisions, which allow the Secretary of the Interior to make supplemental water deliveries at his or her provisions, which allow the Secretary of the Interior to make supplemental water deliveries at his or her
discretion (after consultation with basin states), or through a planning process establishing formal triggers discretion (after consultation with basin states), or through a planning process establishing formal triggers
for Upper Basin water deliveries to Lake Powell, based on agreed-upon hydrological targets. for Upper Basin water deliveries to Lake Powell, based on agreed-upon hydrological targets.
The other primary component of the Upper Basin DCP, the Upper Basin DCP Demand Management The other primary component of the Upper Basin DCP, the Upper Basin DCP Demand Management
Program, has not been formally established. It would entail willing seller/buyer agreements allowing for Program, has not been formally established. It would entail willing seller/buyer agreements allowing for
temporary paid reductions in water use that would provide for more storage volume in Lake Powell. As temporary paid reductions in water use that would provide for more storage volume in Lake Powell. As
noted, the Upper Colorado River Commission operated an Upper Basin System Conservation Pilot noted, the Upper Colorado River Commission operated an Upper Basin System Conservation Pilot
Program from 2015 to 2018; that program compensated water users for temporary, voluntary efforts that Program from 2015 to 2018; that program compensated water users for temporary, voluntary efforts that
resulted in additional water conserved in Lake Powell. A future Upper Basin DCP Demand Management resulted in additional water conserved in Lake Powell. A future Upper Basin DCP Demand Management
Program may expand on some of those efforts. Program may expand on some of those efforts.
Due to falling lake levels, Reclamation implemented drought response operations under DROA that led to Due to falling lake levels, Reclamation implemented drought response operations under DROA that led to
reduced storage in other Upper Basin mainstem reservoirs in 2021 and 2022.reduced storage in other Upper Basin mainstem reservoirs in 2021 and 2022.~~117~~115 Separately, Reclamation Separately, Reclamation
also began planning efforts under DROA, known as the also began planning efforts under DROA, known as the Drought Response Operations Plan, and , and
approved this plan in 2022.approved this plan in 2022.~~118~~116 Reclamation modeling indicates that these efforts, combined with improved Reclamation modeling indicates that these efforts, combined with improved
hydrology in 2023, are expected to stabilize Lake Powell storage levels in the next two hydrology in 2023, are expected to stabilize Lake Powell storage levels in the next two ~~year~~syears (Figure 5).

~~115 U.S. Congress, House Committee on Natural Resources, Subcommittee on Water, Oceans, and Wildlife,~~ ~~Oversight Hearing~~
~~on the Colorado River Drought Contingency Plan, 116th Cong., 1st sess., March 28, 2019, H.Hrg. 116-10 (Washington: GPO,~~
~~2019). Hereinafter, 2019 House Natural Resources DCP Hearing.~~
~~116 While such a mechanism exists for the Lower Basin, a comparable program has not been developed in the Upper Basin.~~
~~117~~3). 115 For example, in 2021, 180,000 AF was transferred to Lake Powell from Flaming Gorge Reservoir (125,000 AF), Blue Mesa For example, in 2021, 180,000 AF was transferred to Lake Powell from Flaming Gorge Reservoir (125,000 AF), Blue Mesa
Reservoir (36,000 AF), and Navajo Reservoir (20,000 AF). Reservoir (36,000 AF), and Navajo Reservoir (20,000 AF).
~~118~~116 For more information, see Reclamation, Colorado River Basin Drought Contingency Plans, at “Drought Response Operations For more information, see Reclamation, Colorado River Basin Drought Contingency Plans, at “Drought Response Operations
Agreement,” at https://www.usbr.gov/dcp/droa.html. Agreement,” at https://www.usbr.gov/dcp/droa.html.
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Figure 53. Lake Powell End-of-Month Elevation Projections
( (~~April and May~~October 2023 24-month study inflow scenarios) 2023 24-month study inflow scenarios)

Source: U.S. Bureau of Reclamation, “24-Month Study Projections,” U.S. Bureau of Reclamation, “24-Month Study Projections,” ~~May~~October 2023, at https://www.usbr.gov/lc/region/g4000/ 2023, at https://www.usbr.gov/lc/region/g4000/
riverops/24ms-projections.html. riverops/24ms-projections.html.
Notes: WY = Water Year. DROA = Drought Response Operations Agreement. WY = Water Year. DROA = Drought Response Operations Agreement.
Lower Basin Drought Contingency Plan
The Lower Basin DCP is designed to require Arizona, California, and Nevada to curtail deliveries and The Lower Basin DCP is designed to require Arizona, California, and Nevada to curtail deliveries and
thereby contribute additional water to Lake Mead storage at predetermined “trigger” elevations. It is also thereby contribute additional water to Lake Mead storage at predetermined “trigger” elevations. It is also
designed to create additional flexibility to incentivize voluntary conservation of water to be stored in Lake designed to create additional flexibility to incentivize voluntary conservation of water to be stored in Lake
Mead, thereby increasing lake levels. Under the DCP, Nevada and Arizona (which were already set to Mead, thereby increasing lake levels. Under the DCP, Nevada and Arizona (which were already set to
have their supplies curtailed beginning at 1,075 feet under the 2007 Interim Guidelines) have committed have their supplies curtailed beginning at 1,075 feet under the 2007 Interim Guidelines) have committed
to contributing additional supplies to maintain higher lake levels (i.e., beyond previous commitments). to contributing additional supplies to maintain higher lake levels (i.e., beyond previous commitments).
These reductions begin at 1,090 feet and would reach their maximums when reservoir levels drop below These reductions begin at 1,090 feet and would reach their maximums when reservoir levels drop below
1,025 feet. The Lower Basin DCP includes—for the first time—delivery cutbacks for California. These 1,025 feet. The Lower Basin DCP includes—for the first time—delivery cutbacks for California. These
curtailments begin with a 200,000 AF delivery reduction at Lake Mead elevations between 1,040 and curtailments begin with a 200,000 AF delivery reduction at Lake Mead elevations between 1,040 and
1,045 feet and would increase by 50,000 AF for each additional 51,045 feet and would increase by 50,000 AF for each additional 5 -foot drop in Lake Mead elevation below foot drop in Lake Mead elevation below
1,040 feet, to as much as 350,000 AF at elevations of 1,025 feet or lower.1,040 feet, to as much as 350,000 AF at elevations of 1,025 feet or lower.
The curtailments are categorized in terms of levels, with Level 1 shortage conditions the term adopted for elevations from 1,050-1,075 feet, and Level 2 conditions the term for elevations between 1,025 feet and 1,050 feet. The curtailments in the Lower Basin DCP are in addition to those agreed to under the 2007 Interim The curtailments in the Lower Basin DCP are in addition to those agreed to under the 2007 Interim
Guidelines and under Minute 323 with Mexico. Specific and cumulative reductions are shown Guidelines and under Minute 323 with Mexico. Specific and cumulative reductions are shown inin Table 12.
In addition to the state-level reductions, under the Lower Basin DCP Reclamation also agreed to pursue In addition to the state-level reductions, under the Lower Basin DCP Reclamation also agreed to pursue
efforts to add 100,000 AF or more of system water within the basin. Some of the largest and most efforts to add 100,000 AF or more of system water within the basin. Some of the largest and most
controversial reductions under the Lower Basin DCP were committed to by Arizona, where pursuant to controversial reductions under the Lower Basin DCP were committed to by Arizona, where pursuant to
previous changes under the 2004 AWSA, a large group of agricultural users were already facing major previous changes under the 2004 AWSA, a large group of agricultural users were already facing major
cutbacks to their CAP water supplies prior to the enactment of DCP. cutbacks to their CAP water supplies prior to the enactment of DCP.
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Table 12. Lower Basin Water Delivery Curtailment Volumes Under Existing Agreements
(values in thousands of acre-feet) (values in thousands of acre-feet)
Binational
2007 Interim
Minute 323
Water
Shortage
Delivery
Scarcity
Total Volume of Curtailment

Guidelines
Reductions
DCP Curtailment
Conting. Plan
(% of Lower Colorado River Apportionment)
Lake Mead
Lower
Elevation (ft)
AZ
NV
Mexico
AZ
NV
CA
Mexico
AZ
NV
CA
Basin
Mexico
1,090 ->1,075 1,090 ->1,075
0 0
0 0
0 0
192 192
8 8
0 0
41 41
192 (6.8%) 192 (6.8%)
8 (2.6%) 8 (2.6%)
0 (0%) 0 (0%)
200 200
41 41
1,075 ->1,050 1,075 ->1,050
320 320
13 13
50 50
192 192
8 8
0 0
30 30
512 (18.2%) 512 (18.2%)
21 (7%) 21 (7%)
0 (0%) 0 (0%)
533 533
80 80
1,050 ->1,045 1,050 ->1,045
400 400
17 17
70 70
192 192
8 8
0 0
34 34
592 (21.1%) 592 (21.1%)
25 (8.3%) 25 (8.3%)
0 (0%) 0 (0%)
617 617
104 104
1,045 ->1,040 1,045 ->1,040
400 400
17 17
70 70
240 240
10 10
200 200
76 76
640 (22.8%) 640 (22.8%)
27 (9.0%) 27 (9.0%)
200 (4.5%) 200 (4.5%)
867 867
146 146
1,040 ->1,035 1,040 ->1,035
400 400
17 17
70 70
240 240
10 10
250 250
84 84
640 (22.8%) 640 (22.8%)
27 (9.0%) 27 (9.0%)
250 (5.6%) 250 (5.6%)
917 917
154 154
1,035 ->1,030 1,035 ->1,030
400 400
17 17
70 70
240 240
10 10
300 300
92 92
640 (22.8%) 640 (22.8%)
27 (9.0%) 27 (9.0%)
300 (6.8%) 300 (6.8%)
967 967
162 162
1,030 - 1,025 1,030 - 1,025
400 400
17 17
70 70
240 240
10 10
350 350
101 101
640 (22.8%) 640 (22.8%)
27 (9.0%) 27 (9.0%)
350 (7.9%) 350 (7.9%)
1,017 1,017
171 171
<1,025 <1,025
480 480
20 20
125 125
240 240
10 10
350 350
150 150
720 (22.8%) 720 (22.8%)
30 (10.0%) 30 (10.0%)
350 (7.9%) 350 (7.9%)
1,100 1,100
275 275
Sources: Table by CRS, using data in the 2007 Interim Shortage Guidelines,Table by CRS, using data in the 2007 Interim Shortage Guidelines, Minute 323 between Mexico and the United States, Minute 323 between Mexico and the United States, Lower Basin Drought Contingency Plan, and , and
the Binational Water Scarcity Contingency Plan in Minute 323 between Mexico and the United States. the Binational Water Scarcity Contingency Plan in Minute 323 between Mexico and the United States.

CRS- CRS-2423

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Management of the Colorado River: Water Allocations, Drought, and the Federal Role

In 2019, at the time of the passage of the Colorado River Drought Contingency Plan In 2019, at the time of the passage of the Colorado River Drought Contingency Plan
Authorization Act, Reclamation asserted that the Lower Basin DCP would significantly reduce Authorization Act, Reclamation asserted that the Lower Basin DCP would significantly reduce
the risk of Lake Mead elevations falling below critical elevation of 1,020 feet.the risk of Lake Mead elevations falling below critical elevation of 1,020 feet.~~119~~117 Combined with Combined with
the commitments from Mexico, total planned cutbacks under shortage scenarios (i.e., all the commitments from Mexico, total planned cutbacks under shortage scenarios (i.e., all
commitments to date, combined) were expected to decrease Lower Basin consumptive use by commitments to date, combined) were expected to decrease Lower Basin consumptive use by
241,000 AF to 1.375 MAF per year, depending on the curtailments triggered by Lake Mead’s 241,000 AF to 1.375 MAF per year, depending on the curtailments triggered by Lake Mead’s
elevation.elevation.~~120~~118 Despite these efforts, Lake Mead has continued to decline since the Lower Basin Despite these efforts, Lake Mead has continued to decline since the Lower Basin
DCP was finalized, and is projected to continue to decline despite improved hydrology in 2023 DCP was finalized, and is projected to continue to decline despite improved hydrology in 2023
(Figure 6). 4). These developments have triggered additional Lower Basin conservation efforts. These developments have triggered additional Lower Basin conservation efforts.
Figure 64. Lake Mead End of Month Elevation Projections
( (~~April and May~~October 2023 24-month study inflow scenarios) 2023 24-month study inflow scenarios)

Source: U.S. Bureau of Reclamation, “24-Month Study Projections,” U.S. Bureau of Reclamation, “24-Month Study Projections,” ~~May~~October 2023, at https://www.usbr.gov/lc/ 2023, at https://www.usbr.gov/lc/
region/g4000/riverops/24ms-projections.html. region/g4000/riverops/24ms-projections.html.
Near-Term Operations: 2023 Draft Supplemental Environmental Impact ~~Statement~~
Statements Many have noted the need for additional “near-term” operational change prior to the expiration of most recent Colorado River agreements in 2026. At a June 14, 2022, Senate hearing, the Commissioner of Reclamation announced that basin At a June 14, 2022, Senate hearing, the Commissioner of Reclamation announced that basin
states would need to conserve states would need to conserve ~~between 2 MAF and 4 MAF in 2023 and 2024~~an additional 2-4 MAF to protect Lake to protect Lake
Mead and Lake Powell storage volumes over the Mead and Lake Powell storage volumes over the ~~near-term (~~2023-20262023-2026~~) period.121 These amounts~~
~~would be in addition to the previous commitments discussed above. At the time, the~~
~~Commissioner noted that if the targets were not met with voluntary actions by the states by~~
~~August 2022, DOI was prepared to act unilaterally.122~~

~~119~~ period.119 117 2019 House Natural Resources DCP Hearing. 2019 House Natural Resources DCP Hearing.
~~120~~118 For a summary of the curtailments that add up to this amount, see “1,090 - >1,075” row For a summary of the curtailments that add up to this amount, see “1,090 - >1,075” row ofof Table 12.
~~121~~119 U.S. Congress, Senate Committee on Energy and Natural Resources, U.S. Congress, Senate Committee on Energy and Natural Resources, Short And Long Term Solutions To Extreme
Drought In The Western U.S., Statement of the Honorable Camille Touton, 117th Cong., 2nd sess., June 14, 2022. , Statement of the Honorable Camille Touton, 117th Cong., 2nd sess., June 14, 2022.
Hereinafter, 2022 Drought Hearing. These amounts were based on a 2022 Reclamation analysis. See Reclamation, Hereinafter, 2022 Drought Hearing. These amounts were based on a 2022 Reclamation analysis. See Reclamation,
~~“Colorado River System Mid Term Projections,” June 16, 2022, at https://www.usbr.gov/ColoradoRiverBasin/~~
~~documents/20220616-ColoradoRiverSystemMid-termProjections-Presentation.pdf.~~
~~122 2022 Drought Hearing.~~(continued...)
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Management of the Colorado River: Water Allocations, Drought, and the Federal Role

The Commissioner noted that if the targets were not met with voluntary actions by the states by August 2022, DOI was prepared to act unilaterally.120 No major water savings commitments were announced in response to Reclamation’s June No major water savings commitments were announced in response to Reclamation’s June
statement.statement.~~123~~ 121 In late October 2022, Reclamation announced its intent to revise the 2007 Interim In late October 2022, Reclamation announced its intent to revise the 2007 Interim
Guidelines in 2023 and 2024 (i.e., prior to post-2026 operational changes to the guidelines, which Guidelines in 2023 and 2024 (i.e., prior to post-2026 operational changes to the guidelines, which
are proceeding separately) are proceeding separately) ~~so as~~ to address continued low runoff conditions in the basin. As part to address continued low runoff conditions in the basin. As part
~~of the proposed guideline modifications, Reclamation published~~ of this process, Reclamation published in the Federal Register its notice of intent to prepare a its notice of intent to prepare a
supplemental environmental impact statement (SEIS) supplemental environmental impact statement (SEIS) ~~in the Federal Register in November~~
~~2022.124 In the SEIS,~~for changes to the 2007 Interim Guidelines.122 Reclamation is analyzing alternatives for three areas of the 2007 guidelines: Reclamation is analyzing alternatives for three areas of the 2007 guidelines:
Lake Mead operations during shortage conditions, coordinated operation of Lake Powell and Lake Mead operations during shortage conditions, coordinated operation of Lake Powell and
Lake Mead, and midyear review for implementation of the operational guidelines.Lake Mead, and midyear review for implementation of the operational guidelines. ~~Reclamation~~
~~indicated that it would, among other things, consider a “framework agreement” alternative~~
~~developed as a “consensus-based” set of actions from states and others.125~~
On January 31, 2023, all of the basin states except California On January 31, 2023, all of the basin states except California ~~submitted a combined proposal for~~
~~Reclamation modeling (the Six State Proposal) in response to the November SEIS notice.126~~
responded to Reclamation’s notice with a combined proposal (the Six State Proposal).123 California submitted its own proposal (the California submitted its own proposal (the California Proposal) separately.) separately.~~127~~124 The Six State The Six State
Proposal requested that Reclamation model in its SEIS 1.543-1.943 MAF per year in newProposal requested that Reclamation model in its SEIS 1.543-1.943 MAF per year in new
delivery reductions on Lower Colorado River Basin delivery reductions on Lower Colorado River Basin ~~contractors (i.e., reductions in addition to~~
~~previous commitments). Those additional reductions would~~contractors, to be implemented through two be implemented through two
mechanisms. First, reductions to account for 1.543 MAF of evaporative losses (referred to as an mechanisms. First, reductions to account for 1.543 MAF of evaporative losses (referred to as an
Infrastructure Protection Volume) would be allocated among Lower Basin contractors and ) would be allocated among Lower Basin contractors and
Mexico, Mexico, ~~which~~and would be assessed at most Lake Mead elevations based on stream reach (i.e., would be assessed at most Lake Mead elevations based on stream reach (i.e.,
position in the basin relative to bodies of water affected by evaporation) and recent consumptive position in the basin relative to bodies of water affected by evaporation) and recent consumptive
use levels.use levels.~~128~~125 Second, additional operational tier changes and delivery reductions are tied to Lake Second, additional operational tier changes and delivery reductions are tied to Lake
Mead elevations of 1,050 feet and lower.Mead elevations of 1,050 feet and lower.~~129~~126 The Six State Proposal’s cumulative reductions from The Six State Proposal’s cumulative reductions from
current levels would current levels would behave been proportionally greater for California than for Arizona and Nevada. proportionally greater for California than for Arizona and Nevada.~~130~~127 For For
its part, the California Proposal would its part, the California Proposal would ~~include~~have included 1.0-1.95 MAF per year in new delivery reductions 1.0-1.95 MAF per year in new delivery reductions
for Lower Basin contractors (not varying based on evaporation), depending on Lake Mead for Lower Basin contractors (not varying based on evaporation), depending on Lake Mead
elevations. These reductions would be phased in on a schedule, starting with 1.0 MAF in elevations. These reductions would be phased in on a schedule, starting with 1.0 MAF in
reductions at a Lake Mead elevation of 1,045 feet, with additional reductions beyond that amount reductions at a Lake Mead elevation of 1,045 feet, with additional reductions beyond that amount
beginning at 1,025 feet. For the first 1.0 MAF, the California Proposal’s reductions would be beginning at 1,025 feet. For the first 1.0 MAF, the California Proposal’s reductions would be
proportionally greater for Arizona and proportionally greater for Arizona and ~~Nevada than for itself; the state also did not assume any~~

~~123~~ “Colorado River System Mid Term Projections,” June 16, 2022, at https://www.usbr.gov/ColoradoRiverBasin/documents/20220616-ColoradoRiverSystemMid-termProjections-Presentation.pdf. 120 2022 Drought Hearing. 121 In a July 18, 2022, letter to Reclamation, the Upper Colorado River Commission declined to contribute a specific In a July 18, 2022, letter to Reclamation, the Upper Colorado River Commission declined to contribute a specific
volume of cutbacks to these efforts, and instead laid out a five-point plan as the basis for its water conservation efforts. volume of cutbacks to these efforts, and instead laid out a five-point plan as the basis for its water conservation efforts.
Letter from Charles Cullom, Director, Upper Colorado River Commission, to Camille Touton, Commissioner, U.S. Letter from Charles Cullom, Director, Upper Colorado River Commission, to Camille Touton, Commissioner, U.S.
Bureau of Reclamation, July 18, 2022, at http://www.ucrcommission.com/wp-content/uploads/2022/07/2022-July-18-Bureau of Reclamation, July 18, 2022, at http://www.ucrcommission.com/wp-content/uploads/2022/07/2022-July-18-
Letter-to-Reclamation.pdf. Letter-to-Reclamation.pdf.
~~124~~122 Bureau of Reclamation, “Notice of Intent To Prepare a Supplemental Environmental Impact Statement for Bureau of Reclamation, “Notice of Intent To Prepare a Supplemental Environmental Impact Statement for
December 2007 Record of Decision Entitled Colorado River Interim Guidelines for Lower Basin Shortages and December 2007 Record of Decision Entitled Colorado River Interim Guidelines for Lower Basin Shortages and
Coordinated Operations For Lake Powell and Lake Mead,” 87Coordinated Operations For Lake Powell and Lake Mead,” 87 Federal Register 69042, November 17, 2022. 69042, November 17, 2022.
Hereinafter, November 2022 Notice. Hereinafter, November 2022 Notice.
~~125 November 2022 Notice.~~
~~126~~123 Letter from Colorado River Basin State Representatives of Arizona, Colorado, Nevada, New Mexico, Utah, and Letter from Colorado River Basin State Representatives of Arizona, Colorado, Nevada, New Mexico, Utah, and
Wyoming to Tanya Trujillo, Assistant Secretary, Water & Science, U.S. Department of the Interior, January 31, 2023. Wyoming to Tanya Trujillo, Assistant Secretary, Water & Science, U.S. Department of the Interior, January 31, 2023.
Hereinafter, Six State Proposal. Hereinafter, Six State Proposal.
~~127~~124 Letter from Colorado River Board of California to Deputy Interior Secretary Tommy Beaudreau et al., U.S. Letter from Colorado River Board of California to Deputy Interior Secretary Tommy Beaudreau et al., U.S.
Department of the Interior, January 31, 2023. Hereinafter, California Proposal. Department of the Interior, January 31, 2023. Hereinafter, California Proposal.
~~128~~125 This amount also assumes the assessment of evaporative losses on Mexico. This amount also assumes the assessment of evaporative losses on Mexico.
~~129~~126 Six State Proposal. These reductions would move the current Tier Six State Proposal. These reductions would move the current Tier 3Three reduction schedule (which begins at 1,025 feet) reduction schedule (which begins at 1,025 feet)
up to a Lake Mead elevation of 1,050 feet, and would institute additional delivery reductions at Lake Mead elevations up to a Lake Mead elevation of 1,050 feet, and would institute additional delivery reductions at Lake Mead elevations
of 1,030 feet or lower. of 1,030 feet or lower.
~~130~~127 CRS analysis of Six State Proposal. CRS analysis of Six State Proposal.
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Nevada than for itself; the state also did not assume any reductions for Mexico.reductions for Mexico.~~131~~128 Both state proposals also Both state proposals also ~~suggest~~suggested changes to Lake Powell’s operational changes to Lake Powell’s operational
tiers to allow more water to be left in that reservoir, although they would do so in different ways. tiers to allow more water to be left in that reservoir, although they would do so in different ways.
~~On April 11, 2023, Reclamation released its draft SEIS.132 The document included~~ Reclamation has released multiple iterations of its draft SEIS in 2023. In April, it released a draft with modeling for a modeling for a
“no action” alternative and two action alternatives.“no action” alternative and two action alternatives.129 Both alternatives would have imposed an equal amount of new reductions in 2024 (0.20-1.166 MAF) tied to Lake Mead elevations.130 The primary difference between the two The primary difference between the two
action alternatives action alternatives iswas the approach for apportioning reductions the approach for apportioning reductions ~~for new shortage operations at~~
~~Lake Mead.~~; Action Alternative 1 Action Alternative 1 ~~assumes additional~~assumed reductions based on priority order of water reductions based on priority order of water
rightsrights~~.133~~,131 whereas Action Alternative 2 Action Alternative 2 ~~assumes~~assumed the Secretary would use existing federal authorities to the Secretary would use existing federal authorities to
impose the same percentage-based delivery reductions on all Lower Basin users, regardless of impose the same percentage-based delivery reductions on all Lower Basin users, regardless of
~~water rights priority.134 Both alternatives would impose an equal amount of additional reductions~~
~~in 2024 (0.20-1.166 MAF), which are tied to Lake Mead elevations. These additional reductions~~
~~would result in cumulative 2024 reductions (i.e., including all prior commitments) of up to 2.083~~
~~MAF. The differing methodologies for the two alternatives would result~~water rights priority.132 This would have resulted in almost all reductions in almost all reductions
being borne by Arizona and Nevada under Alternative 1, whereas Alternative 2 would being borne by Arizona and Nevada under Alternative 1, whereas Alternative 2 would ~~apportion~~have apportioned
reductions among Lower Basin users in all statesreductions among Lower Basin users in all states, based on water usage. based on water usage.~~135~~
~~Reclamation’s draft SEIS also models potential additional curtailments of 0.167-1.917 MAF in~~
~~2025 and 2026 if Lake Mead falls below 1,035 feet in those years (Figure 7). While the 2024~~
~~reductions in the draft SEIS are generally less than those contemplated in the state proposals, the~~
~~2025 and 2026 reductions would be greater than those proposed by the states if adopted and~~
~~added to the 2024 reductions. Table 3 shows how 2025-2026 reductions would be apportioned at~~
~~the state level.~~
~~Table 2. Proposed New 2024 Lower Colorado River Basin State Water Curtailments~~
~~in SEIS Action Alternatives~~
~~Additional Water Delivery Reductions (in 1,000 acre-feet) Beyond Baseline~~

~~Action Alternative 1~~
~~Action Alternative 2~~
~~Lake Mead~~
~~Elevation (ft)~~
AZ
NV
CA
AZ
NV
CA
~~1,090-1,075~~
~~192~~
8
—
75
8
~~117~~
~~1,075-1,050~~
~~511~~
22
—
~~199~~
2
~~313~~
~~1,010-1,045~~
~~593~~
24
—
~~230~~
25
~~362~~
~~1,045-1,040~~
~~1,025~~
42
—
~~324~~
35
~~509~~

~~131 The proposal did not specify the allocation of reductions in excess of 1.0 MAF.~~
~~132~~133 Outside of the approach to Lower Basin shortage operations, the April draft SEIS action alternatives included similar proposals for other areas within the scope of the SEIS. For instance, both alternatives would have altered Lake Powell releases so that, at lower Lake Powell levels, releases would be below the compact’s required average of 7.5 MAF per year (potentially as low as 6.0 MAF per year).134 Both alternatives also would allow for midyear review of Lake Mead hydrology and operations to increase reductions for Lower Basin users outside of the current August determination window for future year operations. On May 22, 2023, DOI announced a consensus-based proposal in which the three Lower Basin states will conserve a total of 3 MAF prior to 2026, with 2.3 MAF of these cuts compensated by the federal government via $4.0 billion in previously appropriated funds in budget reconciliation legislation commonly referred to as the Inflation Reduction Act (IRA; P.L. 117-169).135 This proposal includes total curtailments of 1 MAF per year over three years, with Arizona 128 The proposal did not specify the allocation of reductions in excess of 1.0 MAF. 129 Bureau of Reclamation, Bureau of Reclamation, Near Term Colorado River Operations, Draft Supplemental Environmental Impact , Draft Supplemental Environmental Impact
Statement, April 2023, at https://www.usbr.gov/ColoradoRiverBasin/SEIS.html. Hereinafter, 2023 Draft SEIS. Statement, April 2023, at https://www.usbr.gov/ColoradoRiverBasin/SEIS.html. Hereinafter, 2023 Draft SEIS.
~~133~~130 Reclamation’s April draft SEIS also modeled potential additional curtailments of 0.167-1.917 MAF in 2025 and 2026 if Lake Mead falls below 1,035 feet in those years. 131 As explained in the draft SEIS, “[p]riority refers As explained in the draft SEIS, “[p]riority refers to the distribution of Colorado River water in the Lower Division the distribution of Colorado River water in the Lower Division
States of Arizona, California, and Nevada as subject to laws, judicial rulings and decrees, contracts, interstate States of Arizona, California, and Nevada as subject to laws, judicial rulings and decrees, contracts, interstate
compacts, and operating criteria, known as the “Law of the River,” which apportion available water between the states compacts, and operating criteria, known as the “Law of the River,” which apportion available water between the states
and establish certain priorities in use.” 2023 Draft SEIS at pp. 2-7. and establish certain priorities in use.” 2023 Draft SEIS at pp. 2-7.
~~134~~ 132 The draft SEIS did not include reductions based on evaporation similar to the Six State The draft SEIS did not include reductions based on evaporation similar to the Six State ~~State~~ Proposal, although the Proposal, although the
apportionment of reductions based on water use is in effect similar to the evaporative loss-based approach. apportionment of reductions based on water use is in effect similar to the evaporative loss-based approach.
Additionally, the draft SEIS explains that Alternative 2 incorporates priority-based reductions from the existing 2007 Additionally, the draft SEIS explains that Alternative 2 incorporates priority-based reductions from the existing 2007
Interim Guidelines and 2019 drought contingency plans, and then imposes the same percentage of additional reductions Interim Guidelines and 2019 drought contingency plans, and then imposes the same percentage of additional reductions
to all lower basin users in order to achieve the same total level of reductions as Alternative 1. Ibid., pp. 2-14. to all lower basin users in order to achieve the same total level of reductions as Alternative 1. Ibid., pp. 2-14.
~~135~~133 The Supreme Court has determined the Secretary of the Interior is not bound by a single approach to addressing The Supreme Court has determined the Secretary of the Interior is not bound by a single approach to addressing
Colorado River supply shortages in the Lower Basin. See Arizona v. California, 373 U.S. at 593. The Court stated that Colorado River supply shortages in the Lower Basin. See Arizona v. California, 373 U.S. at 593. The Court stated that
the Secretary may consider reducing Lower Basin deliveries proportionally to statutory allocations of the first 7.5 MAF the Secretary may consider reducing Lower Basin deliveries proportionally to statutory allocations of the first 7.5 MAF
(California 4.4/7.5, Arizona 2.8/7.5, and Nevada 0.3/7.5), but the Secretary also has the authority and discretion to elect (California 4.4/7.5, Arizona 2.8/7.5, and Nevada 0.3/7.5), but the Secretary also has the authority and discretion to elect
an alternate basis for apportioning shortages, subject to statutory constraints. Ibidan alternate basis for apportioning shortages, subject to statutory constraints. Ibid., pp. 592pp. 592~~–593.~~
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~~Management of the Colorado River: Water Allocations, Drought, and the Federal Role~~

~~Action Alternative 1~~
~~Action Alternative 2~~
~~Lake Mead~~
~~Elevation (ft)~~
AZ
NV
CA
AZ
NV
CA
~~1,040-1,035~~
~~1,098~~
56
12
~~435~~
47
~~684~~
~~1,035-1,030~~
~~1,098~~
56
—
~~417~~
45
~~655~~
~~1,030-1,025~~
~~1,098~~
56
—
~~398~~
43
~~625~~
~~1,025-1,000~~
~~1,018~~
53
—
~~367~~
39
~~577~~
~~1,000-975~~
~~1,018~~
53
—
~~367~~
39
~~577~~
~~975-950~~
~~1,018~~
53
—
~~367~~
39
~~577~~
~~<950~~
~~1,018~~
53
—
~~367~~
39
~~577~~
Source: CRS, based on Bureau of Reclamation, Near Term Colorado River Operations, Draft Supplemental
~~Environmental Impact Statement, April 2023.~~
Notes: SEIS = Supplemental Environmental Impact Statement.
~~Figure 7. Modeled Lower Basin Shortages and Existing Contributions,~~
~~2023 Draft SEIS~~
~~Potential Shortage Contributions by Agreement/Source~~

Source: Bureau of Reclamation, Near Term Colorado River Operations, Draft Supplemental Environmental Impact
~~Statement, April 2023.~~
Notes: SEIS = Supplemental Environmental Impact Statement; DCP = Drought Contingency Plan; 2007 ROD =
~~2007 Interim Guidelines Record of Decision.~~
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~~link to page 34~~ ~~Management of the Colorado River: Water Allocations, Drought, and the Federal Role~~

~~Table 3. 2025-2026 Lower Colorado River Basin State Water Cuts~~
~~in SEIS Action Alternatives~~
~~Additional Water Delivery Reductions (in 1,000 acre-feet) Beyond Baseline Agreements~~

~~Action Alternative 1~~
~~Action Alternative 2~~
~~Lake Mead~~
~~Elevation (ft)~~
AZ
NV
CA
AZ
NV
CA
~~1,090-1,075~~
~~192~~
8
—
75
8
~~117~~
~~1,075-1,050~~
~~511~~
22
—
~~199~~
2
~~313~~
~~1,010-1,045~~
~~593~~
24
—
~~230~~
25
~~362~~
~~1,045-1,040~~
~~1,025~~
42
—
~~324~~
35
~~509~~
~~1,040-1,035~~
~~1,098~~
56
12
~~435~~
47
~~684~~
~~1,035-1,030~~
~~1,131~~
63
89
~~479~~
51
~~753~~
~~1,030-1,025~~
~~1,180~~
73
~~230~~
~~554~~
59
~~870~~
~~1,025-1,000~~
~~1,198~~
90
~~612~~
~~709~~
76
~~1,115~~
~~1,000-975~~
~~1,263~~
~~103~~
~~867~~
~~834~~
89
~~1,310~~
~~975-950~~
~~1,329~~
~~117~~
~~1,122~~
~~958~~
~~103~~
~~1,510~~
~~<950~~
~~1,394~~
~~130~~
~~1,376~~
~~1,083~~
~~116~~
~~1,701~~
Source: CRS, based on Bureau of Reclamation, Near Term Colorado River Operations, Draft Supplemental
~~Environmental Impact Statement, April 2023.~~
Notes: SEIS = Supplemental Environmental Impact Statement.
~~Outside of the approach to Lower Basin shortage operations, the action alternatives include~~
~~similar proposals for other areas within the scope of the SEIS. For instance, both alternatives~~
~~would alter Lake Powell releases so that, at lower Lake Powell levels, releases would be below~~
~~the compact’s required average of 7.5 MAF per year (potentially as low as 6.0 MAF per year).136~~
~~Both also would allow for midyear review of Lake Mead hydrology and operations to increase~~
~~reductions for Lower Basin users outside of the current August determination window for future~~
~~year operations.~~
~~On May 22, 2023, DOI announced a consensus-based proposal in which the three Lower Basin~~
~~states will conserve a total of 3 MAF prior to 2026, with 2.3 MAF of these cuts compensated by~~
~~the federal government via $4.0 billion in previously appropriated funds in budget reconciliation~~
~~legislation commonly referred to as the Inflation Reduction Act (IRA; P.L. 117-169).137 The initial~~
~~announcement did not include specific information on allocations of curtailments at the state or~~
~~contractor level, or how these cuts would be tied to specific Lake Mead elevations. DOI stated~~
~~that it will temporarily withdraw the April draft SEIS so it can focus on analyzing the effects of~~
~~the new proposal, with a goal of finalizing the document later this year.138~~

~~136 At Lake Powell elevations between 3,500 and 3,525 feet, releases to the Lower Basin would be maintained at 6.0~~
~~MAF. At elevations below 3,500 feet, releases could be further reduced.~~
~~137 Department of the Interior, “Biden-Harris Administration Announces Historic Consensus System Conservation~~
~~Proposal to Protect the Colorado River Basin,” press release, May 22, 2023, at https://www.doi.gov/pressreleases/~~
~~biden-harris-administration-announces-historic-consensus-system-conservation-proposal. These funds are discussed~~
~~further in the below section, “Funding and Oversight of Existing Facilities and Programs.”~~
~~138 Ibid.~~
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-593. 134 At Lake Powell elevations between 3,500 and 3,525 feet, releases to the Lower Basin would be maintained at 6.0 MAF. At elevations below 3,500 feet, releases could be further reduced. 135 Department of the Interior, “Biden-Harris Administration Announces Historic Consensus System Conservation Proposal to Protect the Colorado River Basin,” press release, May 22, 2023, at https://www.doi.gov/pressreleases/biden-harris-administration-announces-historic-consensus-system-conservation-proposal. These funds are discussed further in the below section, “Funding and Oversight of Existing Facilities and Programs.” Congressional Research Service 26 link to page 31 Management of the Colorado River: Water Allocations, Drought, and the Federal Role contributing 0.28 MAF/year, California contributing 0.40 MAF/year, and Nevada contributing 0.07 MAF/year, all regardless of reservoir conditions. The states requested, and DOI agreed, to temporarily withdraw the April draft SEIS so the department could focus on analyzing the effects of the new proposal, with a goal of finalizing the document in late 2023.136 Reclamation released a new draft SEIS in October 2023 with two options: a No Action Alternative and a Proposed Action alternative consisting of the consensus-based proposal. Table 3 shows state level commitments under both options. At the time, Reclamation noted that improved hydrology had significantly decreased the chances of critical elevations at both reservoirs.137 Table 3. Curtailment Alternatives Through 2026 in October 2023 Draft SEIS (curtailment amounts in thousands of acre-feet [KAF]) Proposed Action: 2007 ROD, 2019 No Action: 2007 ROD, 2019 DCP DCP, Lower Division Proposal (curtailments in KAF) (curtailments in KAF) Lake Mead Elevation (Feet) AZ NV CA Total AZ NV CA Total 1,090 - 192 8 — 200 472 78 400 950 >1,075 1,075 - 512 21 — 533 792 91 400 1,283 >1,050 1,050 - 592 25 — 617 872 95 400 1,367 >1,045 1,045 - 640 27 200 867 920 97 600 1,617 >1,040 1,040 - 640 27 250 917 920 97 650 1,667 >1,035 1,035 - 640 27 300 967 920 97 700 1,717 >1,030 1,030 - 640 27 350 1,017 920 97 750 1,767 1,025 <1,025 640 27 350 1,100 1,000 100 750 1,850 Source: Bureau of Reclamation, Department of the Interior, Near-Term Colorado River Operations, Revised Draft Supplemental Environmental Impact Statement, October 2023, at https://www.usbr.gov/ColoradoRiverBasin/documents/NearTermColoradoRiverOperations/20231019-Near-termColoradoRiverOperations-RevisedDraftEIS-508.pdf. Notes: SEIS = Supplemental Environmental Impact Statement; 2007 ROD = Record of Decision for 2007 Interim Shortage Guidelines; 2019 DCP = 2019 Drought Contingency Plan for Lower Colorado River Basin; Lower Division Proposal = April 2023 Consensus Proposal by Lower Colorado River Basin States. 136 Ibid. 137 Bureau of Reclamation, Department of the Interior, Near-Term Colorado River Operations, Revised Draft Supplemental Environmental Impact Statement, October 2023, at https://www.usbr.gov/ColoradoRiverBasin/documents/NearTermColoradoRiverOperations/20231019-Near-termColoradoRiverOperations-RevisedDraftEIS-508.pdf. Congressional Research Service 27 Management of the Colorado River: Water Allocations, Drought, and the Federal Role Post-2026 Operations Parallel to the process analyzing potential near-term operational changes, in 2022 Reclamation initiated efforts to study and recommend alternatives for long-term (post-2026) operations on the Colorado River. 138 Most of the major agreements discussed herein are scheduled to expire in 2026, and the post-2026 operational planning process is expected to identify a range of alternatives to be employed in Colorado River management for decades into the future. In the fall of 2023, Reclamation released a scoping report summarizing thousands of comments received on post-2026 operations and stated its intent to finalize draft alternatives under this process by late 2024.139
Issues for Congress
Funding and Oversight of Existing Facilities and Programs
The principal role of Congress as it relates to storage facilities on the Colorado River is funding The principal role of Congress as it relates to storage facilities on the Colorado River is funding
and oversight of facility operations, construction, and programs to protect and restore listed and oversight of facility operations, construction, and programs to protect and restore listed
species (e.g., Glen Canyon Dam Adaptive Management Program and the Upper Colorado River species (e.g., Glen Canyon Dam Adaptive Management Program and the Upper Colorado River
Endangered Fish Program). In the Upper Basin, Colorado River facilities include the 17 active Endangered Fish Program). In the Upper Basin, Colorado River facilities include the 17 active
participating units in the Colorado River Storage Projects, as well as the Navajo-Gallup Water participating units in the Colorado River Storage Projects, as well as the Navajo-Gallup Water
Supply Project. In the Lower Basin, major facilities include the Salt River Project and Theodore Supply Project. In the Lower Basin, major facilities include the Salt River Project and Theodore
Roosevelt Dam, Hoover Dam and All-American Canal, Yuma and Gila Projects, Parker-Davis Roosevelt Dam, Hoover Dam and All-American Canal, Yuma and Gila Projects, Parker-Davis
Project, Central Arizona Project, and Robert B. Griffith Project (now Southern Nevada Water Project, Central Arizona Project, and Robert B. Griffith Project (now Southern Nevada Water
System). System).
Congressional appropriations in support of Colorado River projects and programs typically Congressional appropriations in support of Colorado River projects and programs typically
account for a portion of overall project budgets. For example, in FY2020, approximately 40% of account for a portion of overall project budgets. For example, in FY2020, approximately 40% of
Lower Colorado River Region’s overall budget was funded with discretionary appropriations, Lower Colorado River Region’s overall budget was funded with discretionary appropriations,
with the remainder of funding coming from power revenues (which are made available without with the remainder of funding coming from power revenues (which are made available without
further appropriation) and nonfederal partners.further appropriation) and nonfederal partners.~~139 In recent years,~~140 Congress has also authorized Congress has also authorized
and appropriated funding and appropriated funding ~~that has targeted~~for the Colorado River Basin in general (e.g., the Pilot the Colorado River Basin in general (e.g., the Pilot
~~System Conservation Plan). Congress may choose to extend or amend authorities specific to the~~
~~basin or alter basin funding levels.~~
~~While discretionary appropriations for the Colorado River are of ongoing interest to Congress,~~
System Conservation Plan). Congress has also addressed Colorado River funding outside of the regular appropriations Congress has also addressed Colorado River funding outside of the regular appropriations
process. In the 117th Congress, in Section 50233 of the IRAprocess. In the 117th Congress, in Section 50233 of the IRA, Congress provided $4.0 billion for Congress provided $4.0 billion for
projects that mitigate drought in the 17 arid and semiarid projects that mitigate drought in the 17 arid and semiarid reclamation states in the West, in the West,~~140~~141 with with
priority given to Colorado River Basin activities. This funding is available through FY2026 and priority given to Colorado River Basin activities. This funding is available through FY2026 and
may be used for a variety of activities, including some of the previously authorized activities may be used for a variety of activities, including some of the previously authorized activities
discussed above and as compensation for the delivery reductions announced in May 2023. discussed above and as compensation for the delivery reductions announced in May 2023.
Reclamation announced initial plans for this funding on October 12, 2022, in the form of a new Reclamation announced initial plans for this funding on October 12, 2022, in the form of a new
138 More information on Reclamation’s process for post-2026 operational planning is available at https://www.usbr.gov/ColoradoRiverBasin/post2026/index.html. 139 Bureau of Reclamation, Scoping Report for POst-2026 Colorado River Reservoir Operations, October 2023, at https://www.usbr.gov/ColoradoRiverBasin/documents/post2026/scoping/Post2026Operations_ScopingReport_October2023_508.pdf. 140 Reclamation, Lower Colorado Region Annual Report, Fiscal Years 2019 & 2020. 141 Reclamation states refers to the 17 states designated by Congress to be in the Reclamation service area, pursuant to the Reclamation Act of 1902, as amended. 34 Stat. 259. Congressional Research Service 28 Management of the Colorado River: Water Allocations, Drought, and the Federal Role program, the Lower Colorado River Basin System Conservation and Efficiency Program.142program, the Lower Colorado River Basin System Conservation and Efficiency Program~~.141~~ The The
program has three components: program has three components:
• Under the first component (1a), Colorado River water delivery contractors or • Under the first component (1a), Colorado River water delivery contractors or
entitlement holders submitted proposals resulting in water remaining in Lake entitlement holders submitted proposals resulting in water remaining in Lake
Mead at a set price of $330 per acre-foot for a one-year agreement, $365 per Mead at a set price of $330 per acre-foot for a one-year agreement, $365 per
acre-foot for a two-year agreement, and $400 per acre-foot for a three-year acre-foot for a two-year agreement, and $400 per acre-foot for a three-year
agreement. These proposals were due in November 2022. agreement. These proposals were due in November 2022.
• For the second component (1b), Reclamation accepted proposals for additional • For the second component (1b), Reclamation accepted proposals for additional
water conservation and efficiency projects that could involve a variety of pricing water conservation and efficiency projects that could involve a variety of pricing
options as proposed by Colorado River water delivery contractors or entitlement options as proposed by Colorado River water delivery contractors or entitlement
holders. These proposals were due in November 2022. holders. These proposals were due in November 2022.

~~139 Reclamation, Lower Colorado Region Annual Report, Fiscal Years 2019 & 2020.~~
~~140 Reclamation states refers to the 17 states designated by Congress to be in the Reclamation service area, pursuant to~~
~~the Reclamation Act of 1902, as amended. 34 Stat. 259.~~
~~141 Reclamation, “Biden-Harris Administration Announces New Steps for Drought Mitigation Funding from Inflation~~
~~Reduction Act,” Press Release, October 12, 2022, at https://www.usbr.gov/newsroom/news-release/4353.~~
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• The third component (2) would allow for proposals to be submitted in early 2023 • The third component (2) would allow for proposals to be submitted in early 2023
for long-term system efficiency improvements that will result in multi-year for long-term system efficiency improvements that will result in multi-year
system conservation. These proposals were expected to be solicited in early 2023. system conservation. These proposals were expected to be solicited in early 2023.
While some agreements under this program have been announced, While some agreements under this program have been announced,~~142~~143 the full magnitude of water the full magnitude of water
savings that might result from these voluntary agreements is unclear. If the agreements are savings that might result from these voluntary agreements is unclear. If the agreements are
successful, future federal funding similar to that provided in the IRA may continue to be successful, future federal funding similar to that provided in the IRA may continue to be
requested to mitigate the effect of long-term drought in the basin and the shift away from current requested to mitigate the effect of long-term drought in the basin and the shift away from current
water consumption levels. water consumption levels.
In addition to the aforementioned new program being implemented with IRA funding, the In addition to the aforementioned new program being implemented with IRA funding, the
Administration also announced that $250 million of the act’s funding would go toward Salton Sea Administration also announced that $250 million of the act’s funding would go toward Salton Sea
restoration activities over the 2022-2026 timeframe.restoration activities over the 2022-2026 timeframe.~~143~~144 Restoration of the Sea is a Restoration of the Sea is a ~~high~~ priority of priority of
the Imperial Irrigation District, one of the largest water rights holders on the Colorado River.the Imperial Irrigation District, one of the largest water rights holders on the Colorado River.~~144~~145
Tribal Water Rights Settlements and Leasing
Many tribal water rights are senior to other water rights in the basin, and thus are likely to play an Many tribal water rights are senior to other water rights in the basin, and thus are likely to play an
important role in the future of the Colorado River. The extent to which tribes develop their water important role in the future of the Colorado River. The extent to which tribes develop their water
rights, or are willing and able to market their water to other users, has ramifications for water rights, or are willing and able to market their water to other users, has ramifications for water
availability in the basin. The 117th Congress authorized a new Indian water rights settlement availability in the basin. The 117th Congress authorized a new Indian water rights settlement
related to one tribe’s rights to Colorado River water (the Hualapai Settlement,) and enacted a new related to one tribe’s rights to Colorado River water (the Hualapai Settlement,) and enacted a new
authority for the Colorado River Indian Tribes, one of the largest water rights holders on the river, authority for the Colorado River Indian Tribes, one of the largest water rights holders on the river,
to enter into agreements to lease a portion of the tribes’ Colorado River water (the Colorado River to enter into agreements to lease a portion of the tribes’ Colorado River water (the Colorado River
Indian Tribes Water Resiliency Act of 2022,).Indian Tribes Water Resiliency Act of 2022,).~~145~~146 As previously noted, Congress has approved 142 Bureau of Reclamation, “Biden-Harris Administration Announces New Steps for Drought Mitigation Funding from Inflation Reduction Act,” Press Release, October 12, 2022, at https://www.usbr.gov/newsroom/news-release/4353. 143 ~~As previously noted, Congress has approved~~
~~Indian water rights settlements associated with more than 2.5 MAF of tribal diversion rights on~~
~~the Colorado River (these rights are a subset of the water allocations per state in which they are~~
~~located); a portion of this water has been developed to date. Congress may be asked to consider~~
~~new settlements that would add to this total.~~
~~New Facilities and Other Alterations~~
~~Some states may pursue further development of their unused Colorado River water (i.e., rather~~
~~than cutting their use). For example, one project that would develop Upper Basin waters, the~~
~~proposed Lake Powell Pipeline (LPP), would direct approximately 86,000 AF of Utah’s Upper~~
~~Basin Colorado River Basin annual apportionment from Lake Powell to Washington County, UT~~
~~(i.e., the St. George, UT, area, which is technically located within the Lower Basin drainage~~

~~142~~ For example, in April 2023, the Biden Administration announced an agreement with the Gila River Indian For example, in April 2023, the Biden Administration announced an agreement with the Gila River Indian
Community to conserve 125,000 AF of water per year (for three years) with $50 million of IRA funding, as well as an Community to conserve 125,000 AF of water per year (for three years) with $50 million of IRA funding, as well as an
agreement with the Coachella Valley Water District to conserve 30,000 AF of water per year (for three years) with $12 agreement with the Coachella Valley Water District to conserve 30,000 AF of water per year (for three years) with $12
million in IRA funding. See White House, “Fact Sheet: Biden-⁠Harris Administration Announces New Investments to million in IRA funding. See White House, “Fact Sheet: Biden-⁠Harris Administration Announces New Investments to
Protect the Colorado River System,” April 6, 2023. Protect the Colorado River System,” April 6, 2023.
~~143~~144 Bureau of Reclamation, “Inflation Reduction Act Funds Landmark Agreements to Accelerate Salton Sea Restoration,” Press Reclamation, “Inflation Reduction Act Funds Landmark Agreements to Accelerate Salton Sea Restoration,” Press
Release, November 28, 2022, at https://www.usbr.gov/newsroom/news-release/4380. Release, November 28, 2022, at https://www.usbr.gov/newsroom/news-release/4380.
~~144~~145 For more on Salton Sea restoration, see CRS In Focus IF11104, For more on Salton Sea restoration, see CRS In Focus IF11104, Salton Sea Management and Restoration Efforts, by , by
Pervaze A. Sheikh and Charles V. Stern. Pervaze A. Sheikh and Charles V. Stern.
~~145~~146 Prior to the legislation’s enactment, these tribes, who were awarded their water rights under the Arizona v. Prior to the legislation’s enactment, these tribes, who were awarded their water rights under the Arizona v.
CaliforniaCalifornia decree, were not able to lease their water. This is not the case for most other tribes with Colorado River decree, were not able to lease their water. This is not the case for most other tribes with Colorado River
water rights. water rights.
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Indian water rights settlements associated with more than 2.5 MAF of tribal diversion rights on the Colorado River (these rights are a subset of the water allocations per state in which they are located); a portion of this water has been developed to date. Congress may be asked to consider new settlements that would add to this total. New Facilities and Other Alterations Some states may pursue further development of their unused Colorado River water (i.e., rather than cutting their use). For example, one project that would develop Upper Basin waters, the proposed Lake Powell Pipeline (LPP), would direct approximately 86,000 AF of Utah’s Upper Basin Colorado River Basin annual apportionment from Lake Powell to Washington County, UT (i.e., the St. George, UT, area, which is technically located within the Lower Basin drainage area).147~~area).146~~ The pipeline would begin near Glen Canyon Dam in Arizona and would run through The pipeline would begin near Glen Canyon Dam in Arizona and would run through
Arizona and Utah to Sand Hollow Reservoir near St. George, UT. Reclamation is the lead agency Arizona and Utah to Sand Hollow Reservoir near St. George, UT. Reclamation is the lead agency
for the project under NEPA and is coordinating an environmental impact statement (EIS) for the for the project under NEPA and is coordinating an environmental impact statement (EIS) for the
most recently proposed version of the project.most recently proposed version of the project.~~147~~148
The debate over the Lake Powell Pipeline is illustrative of the issues future water development The debate over the Lake Powell Pipeline is illustrative of the issues future water development
proposals may face in the basin. Supporters argue that the pipeline is needed to provide a proposals may face in the basin. Supporters argue that the pipeline is needed to provide a
secondary water source for the St. George area (in addition to its primary water source from the secondary water source for the St. George area (in addition to its primary water source from the
Virgin River). However, environmental groups have argued that the proposed development and Virgin River). However, environmental groups have argued that the proposed development and
diversion of additional Upper Basin waters is ill-advised in light of climate change and the basin’s diversion of additional Upper Basin waters is ill-advised in light of climate change and the basin’s
over-allocation.over-allocation.~~148~~149 The six other Colorado River Basin states have raised concerns related to the The six other Colorado River Basin states have raised concerns related to the
proposed LPP’s “legal and operational issues,” and have criticized the use of the LPP NEPA proposed LPP’s “legal and operational issues,” and have criticized the use of the LPP NEPA
process as a de facto forum for resolving a conflict among basin states. The six states previously process as a de facto forum for resolving a conflict among basin states. The six states previously
requested that Reclamation refrain from issuing a final EIS until these issues can be resolved on a requested that Reclamation refrain from issuing a final EIS until these issues can be resolved on a
consensus basis.consensus basis.~~149~~150
Some groups that oppose new infrastructure development on the Colorado River also have Some groups that oppose new infrastructure development on the Colorado River also have
proposed demolition of proposed demolition of existing infrastructure, in particular Glen Canyon Dam. They argue that infrastructure, in particular Glen Canyon Dam. They argue that
removing the dam would be beneficial to listed species and the Grand Canyon’s ecosystem and removing the dam would be beneficial to listed species and the Grand Canyon’s ecosystem and
would be a cheaper and less politically problematic option than other options (e.g., fallowing would be a cheaper and less politically problematic option than other options (e.g., fallowing
Upper Basin farms to conserve water).Upper Basin farms to conserve water).~~150~~151 For their part, water and power users and most For their part, water and power users and most
governmental entities oppose these efforts for their potential negative economic impact. governmental entities oppose these efforts for their potential negative economic impact.
Reclamation reports that it is accelerating maintenance actions at Glen Canyon Dam to determine Reclamation reports that it is accelerating maintenance actions at Glen Canyon Dam to determine
the reliability of using river bypass tubes at the dam to enable Lower Basin releases at storage the reliability of using river bypass tubes at the dam to enable Lower Basin releases at storage
levels below minimum power pool.levels below minimum power pool.~~151~~152 Reclamation is also studying the efficacy of physical 147 ~~Reclamation is also studying the efficacy of physical~~
~~modifications to Glen Canyon Dam to allow for releases below critical elevations.152 Removing~~
~~or significantly altering Glen Canyon Dam would likely require authorization by Congress.~~
~~Post-2026 Operations/Agreements~~
~~Congress is likely to remain interested in the status of long-term drought in the basin and in the~~
~~implementation of the DCPs and other related agreements, including their ability to stem further~~
~~delivery curtailments and add water to the basin’s storage reservoirs.153 Congress also may be~~

~~146~~ While St. George, UT, is technically within the Lower Colorado River Basin’s drainage, Utah’s state allocation While St. George, UT, is technically within the Lower Colorado River Basin’s drainage, Utah’s state allocation
comes out of waters available to the Upper Basin. Thus, the LPP would utilize Upper Basin waters. comes out of waters available to the Upper Basin. Thus, the LPP would utilize Upper Basin waters.
~~147~~148 For project NEPA documents and studies, see https://www.usbr.gov/uc/DocLibrary/ For project NEPA documents and studies, see https://www.usbr.gov/uc/DocLibrary/
EnvironmentalImpactStatements/LakePowellPipeline/index.html#intro. EnvironmentalImpactStatements/LakePowellPipeline/index.html#intro.
~~148~~149 Letter from Utah Rivers Council et al. to Rick Baxter, Program Manager, Bureau of Reclamation Provo Area Office, Letter from Utah Rivers Council et al. to Rick Baxter, Program Manager, Bureau of Reclamation Provo Area Office,
September 8, 2020. September 8, 2020.
~~149~~150 Letter from Colorado River Basin States Representatives of Arizona, California, Colorado, Nevada, New Mexico, Letter from Colorado River Basin States Representatives of Arizona, California, Colorado, Nevada, New Mexico,
and Wyoming to Secretary of the Interior David Bernhardt, September 8, 2020. and Wyoming to Secretary of the Interior David Bernhardt, September 8, 2020.
~~150~~151 Save the Colorado, “Save the Colorado’s Policies for Renegotiation of the 2007 Interim Guidelines for Management Save the Colorado, “Save the Colorado’s Policies for Renegotiation of the 2007 Interim Guidelines for Management
of the Colorado River,” Press Release, November 29, 2022. of the Colorado River,” Press Release, November 29, 2022.
~~151~~152 Bureau of Reclamation, “Interior Department Announces Actions to Protect Colorado River System, Sets 2023 Operating Reclamation, “Interior Department Announces Actions to Protect Colorado River System, Sets 2023 Operating
~~Conditions for Lake Powell and Lake Mead,” August 16, 2022.~~
~~152 Ibid.~~
~~153 For instance, 2021 and 2022 hearings on drought in the western United States included extensive discussion of~~
~~drought conditions in the Colorado River Basin. See U.S. Congress, House Committee on Natural Resources,~~
~~Subcommittee on Water, Oceans, and Wildlife,~~ ~~The Status of Drought Conditions Throughout the Western United~~
~~States, 117th Cong., 1st sess., May 25, 2021 and U.S. Congress, Senate Committee on Energy and Natural Resources,~~
Short and Long-Term Solutions to Extreme Drought in the Western United States, 117th Cong., 2nd sess., June 14, 2022.
Conditions for Lake Powell and Lake Mead,” August 16, 2022. Congressional Research Service Congressional Research Service

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~~interested in broader basin planning. Federally led efforts to finalize operational changes~~
~~proposed in the 2023 draft SEIS, and to extend the 2007 Interim Guidelines (including the DCPs)~~
~~beyond the end of 2026, will frame future management of the Colorado River. New agreements~~
~~that would protect water supplies in both the short and long term may result in additional~~
~~congressional involvement in basin management in the form of oversight and the consideration of~~
~~new authorities and/or funding.~~
modifications to Glen Canyon Dam to allow for releases below critical elevations.153 Removing or significantly altering Glen Canyon Dam would likely require authorization by Congress. Concluding Observations
There is wide acknowledgement that existing directives for managing Colorado River Basin There is wide acknowledgement that existing directives for managing Colorado River Basin
waters are inadequate to address the ongoing persistent drought and water uses and do not waters are inadequate to address the ongoing persistent drought and water uses and do not
account for the basin’s current and projected hydrology. The original basis for the Colorado River account for the basin’s current and projected hydrology. The original basis for the Colorado River
Compact assumed more water than turned out to be available for consumptive uses, and Compact assumed more water than turned out to be available for consumptive uses, and a drought drought
~~dating to 2000~~in the basin has exacerbated this issue. Although recent agreements have marginally reduced has exacerbated this issue. Although recent agreements have marginally reduced
usage, basin-wide consumptive use (including evaporation) has continued to exceed natural flows usage, basin-wide consumptive use (including evaporation) has continued to exceed natural flows
in most years. The resulting drawdown of basin storage has in most years. The resulting drawdown of basin storage has ~~left Lakes Mead and Powell at~~
~~historically low levels that threaten~~threatened both hydropower production and water deliveries both hydropower production and water deliveries ~~throughout~~
~~the basin. Water~~. Long-term flow projections estimate that flow projections estimate that ~~flows~~available supplies will continue to decrease, whereas new will continue to decrease, whereas new
demands and diversions (e.g., development of tribal water rights) suggest that competition for this demands and diversions (e.g., development of tribal water rights) suggest that competition for this
water among users will continue to increase. water among users will continue to increase.
Despite agreement that some level of water delivery cutbacks will be necessary to protect power Despite agreement that some level of water delivery cutbacks will be necessary to protect power
generation and reservoir storage, there remain considerable differences of opinion as to what form generation and reservoir storage, there remain considerable differences of opinion as to what form
these actions should take. The question of which entities to subject to water delivery reductions these actions should take. The question of which entities to subject to water delivery reductions
and of what magnitude, as well as what sort of mitigation might accompany these efforts, take on and of what magnitude, as well as what sort of mitigation might accompany these efforts, take on
an added level of urgency due to the river’s economic importance to many areas. The relative an added level of urgency due to the river’s economic importance to many areas. The relative
importance of established water rights priorities in the basin, compared to priority for health, importance of established water rights priorities in the basin, compared to priority for health,
safety, and other uses, is a central issue currently facing decisionmakers. Other questions—safety, and other uses, is a central issue currently facing decisionmakers. Other questions—
including how much funding, if any, federal and state governments should provide users including how much funding, if any, federal and state governments should provide users ~~for long-~~
~~term water cutbacks~~to forgo water deliveries—are also likely to figure prominently into future discussions. Changes to —are also likely to figure prominently into future discussions. Changes to
infrastructure and alterations to basin accounting are other likely items for debate in future basin infrastructure and alterations to basin accounting are other likely items for debate in future basin
negotiations.negotiations.
153 Ibid. Congressional Research Service 31 Management of the Colorado River: Water Allocations, Drought, and the Federal Role

Author Information

Charles V. Stern Charles V. Stern
Kristen Hite Kristen Hite
Specialist in Natural Resources Policy Specialist in Natural Resources Policy
Legislative Attorney Legislative Attorney

Pervaze A. Sheikh Pervaze A. Sheikh

Specialist in Natural Resources Policy Specialist in Natural Resources Policy

~~Congressional Research Service~~

33

~~Management of the Colorado River: Water Allocations, Drought, and the Federal Role~~

Disclaimer
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Congressional Research Service Congressional Research Service
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