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

Management of the Colorado River: Water
September 7, 2022May 2, 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

Apportioned Colorado River water is widely acknowledged to be in excess of the river’s natural
flows, and consumptive use of these waters typically exceeds natural flows. This causes an

imbalance in the basin’s available water supply and demand. Stress on basin water supplies is
exacerbated by a long-term drought dating to 2000.
River Management
Multiple laws, court decisions, and other documents govern Colorado River operations; the foundational document governing
basin water management isRiver Management Kristen Hite A collection of compacts, treaties, statutes, and other authorities govern Colorado River Legislative Attorney allocations and apportionments. The foundational management document, the Colorado River Compact of 1922, the Colorado River Compact of 1922. Pursuant to the compact, the basin states established a established a
framework to apportion water supplies between the river’s Upper and Lower Basins, framework to apportion water supplies between the river’s Upper and Lower Basins, with the dividing line between the two
basinsdivided at Lee Ferry, AZ. at Lee Ferry, AZ. Each basin wasThe compact allocated 7.5 million acre-feet (MAF) allocated 7.5 million acre-feet (MAF) annually under the compact, and For a copy of the full report, annually to each basin, and a 1994 treaty made an additional an additional
1.5 MAF in annual flows was made available to Mexico under a 1944 treaty. Further agreements and court decisions
addressed other issues, and subsequent federal legislation provided authority and funding for federal facilities that allowed
users to develop their allocations. A 1963 Supreme Court ruling confirmed that Congress designated the Secretary of the
Interior as the water master for the Lower Basin, a role in which the federal government manages the delivery of all water
below Hoover Dam.
1.5 MAF in annual flows available please call 7-5700 or visit to Mexico. A Supreme Court case and related decrees inform the Secretary of the Interior’s www.crs.gov. management of the delivery of all water below Hoover Dam. Apportioned Colorado River water is in excess of the river’s natural flows, and actual consumptive use plus other water losses (e.g., evaporation) typically exceeds natural flows. This imbalance has stressed basin water supplies, exacerbated by a long-term drought dating to 2000. Reclamation and basin stakeholders closely track the status of two large reservoirs—Lake Powell in the Upper Basin and Reclamation and basin stakeholders closely track the status of two large reservoirs—Lake Powell in the Upper Basin and
Lake Mead in the Lower Basin—as Lake Mead in the Lower Basin—as an indicatorindicators of basin storage conditions. Under criteria agreed upon by basin states, water of basin storage conditions. Under criteria agreed upon by basin states, water
releases from both lakes are tied to specific water storage levels. releases from both lakes are tied to specific water storage levels. In recent years, storage levels have been falling. In August
2021Since the onset of drought in the early 2000s, storage levels at these reservoirs have been falling; in 2021 and 2022, Reclamation declared the first-ever , Reclamation declared the first-ever LevelTier One and Tier Two Shortages One Shortage Condition in the Lower Basin; it subsequently declared a Level
Two Shortage Condition in August 2022. These declarationsin the Lower Basin. These designations reduced water deliveries to contractors in Arizona and Nevada, reduced water deliveries to contractors in Arizona and Nevada,
as well as to Mexico. as well as to Mexico. Also in 2022, Lake Powell’s surface water elevation fell below a key target (3,525 feet) established to
protect hydropower infrastructure at Glen Canyon Dam. In response, Reclamation has implemented drought response
operations intended to protect Lake Powell elevationsIn the Upper Basin, Lake Powell’s storage has also continued to drop. This trend could soon jeopardize hydropower generation at Glen Canyon Dam and has led to operational changes in the Upper Basin. .
Efforts to Address Drought
The federal government has led multiple efforts The federal government has led multiple efforts attempting to improve the basin’s water supply outlook, resulting in to improve the basin’s water supply outlook, resulting in
collaborative agreements in 2003 and 2007collaborative agreements in 2003 and 2007, and most recently in and the 2019 drought contingency plans (DCPs) for the Upper the 2019 drought contingency plans (DCPs) for the Upper
and Lower Colorado River and Lower Colorado River Basins. Basins. The latter agreements were authorized by Congress in the Colorado River Drought
Contingency Plan Authorization Act (P.L. 116-14). The DCPs required reduced Lower Basin water deliveries tied to
specified storage levels, committed Reclamation to additional water conservation efforts, and put in place plans to coordinate
Upper Basin operations to enhance Lake Powell storage levels and prevent the loss of hydropower generation.
The hydrologic outlook for the Colorado River Basin has deteriorated further since The hydrologic outlook for the Colorado River Basin has deteriorated further since passageapproval of the DCPs of the DCPs, and there remains. Due to 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 with two action alternatives that would both, among other things, impose additional water delivery cutbacks on Lower Basin contractors in 2024-2026. The alternatives differ primarily in how they allocate water cuts—sharing the cuts among all Lower Basin users in one case or based on the priority of water rights in the other. Any decision on this question could also affect longer-term (i.e., post-2026) operational guidelines. Congressional Role
widespread concern about the basin’s long-term water supply. On June 14, 2022, Reclamation called for basin states to
conserve an additional 2-4 MAF of water in 2023; this could lead to further reduced deliveries to contractors in the near term.
In addition to short-term water management, longer-term questions facing decisionmakers include whether to renew and/or
amend basin water management agreements (including the DCPs) prior to their expiration in 2026. Some worry that the
current convergence of basin issues could result in the basin’s first-ever compact call (i.e., an attempt to force deliveries of
Colorado River water).
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Congressional Role
Congress plays a multifaceted role in federal management of the Colorado River Basin. Congress funds and oversees Congress funds and oversees
management of basin management of basin facilities and has held oversight hearings on drought in the basin and elsewherewater and power facilities. Congress . Congress also has has
enacted legislation enacted legislation involving allocation of affecting Colorado River waters (e.g., Colorado River waters (e.g., authorization of Indian water rights settlements; new Indian water rights settlements; new
water storage facilities) and water storage facilities) and authorities to mitigate water shortages (i.eauthorizing water shortage mitigation (e.g., the DCPs and other related efforts). ., the DCPs and other related efforts). Further,
Congress may consider amending, extending, or repealing these authorities or addressing the sufficiency of funding to
combat long-term water shortages. Most recently, in Section 50233 of P.L. 117-169 (popularly known as the Inflation Section 50233 of P.L. 117-169 (popularly known as the Inflation
Reduction Act)Reduction Act), Congress provided $4.0 billion for drought mitigation in the West, with priority given to Colorado River provided $4.0 billion for drought mitigation in the West, with priority given to Colorado River
Basin activities.Basin activities.
Congress may consider further amending existing authorities or funding mitigation activities for basin’s water shortages. Congressional Research Service Congressional Research Service

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Contents
Introduction ..................................................................................................................................... 1
The Law of the River: Foundational Documents and Programs ..................................................... 3
Colorado River Compact ........................................................................................................... 4
Boulder Canyon Project Act ...................................................................................................... 5
Arizona Ratification and Arizona v. California Decision 4 1944 U.S.-Mexico Water Treaty ........................................................................................ 5
1944 U.S.-Mexico Water Treaty ........ 5 Arizona v. California .............................................................................................................. 6... 5
Upper Basin Compact and Colorado River Storage Project Authorizations ............................. 67 Colorado River Basin Project Act of 1968 .............................................................................. 10
Water Storage and Operations ......................................................................................................... 8 11
Annual Operations .................................................................................................................... 9 11
Recent Conditions ............................................................................................................. 1012
Mitigating the Environmental Effects of Colorado River Basin Development .............................. 11 13
Salinity Control ........................................................................................................................ 11 13
Endangered Species Efforts and Habitat Improvements ......................................................... 1213
Upper Colorado Endangered Fish Recovery Program ...................................................... 1214
San Juan River Basin Recovery Implementation Program ............................................... 1314
Glen Canyon Dam Adaptive Management Program ......................................................... 1314
Lower Colorado Multi-Species Conservation Program .................................................... 1315
Tribal Water Rights ........................................................................................................................ 1416
Drought and the Supply/Demand Imbalance................................................................................. 1517
Recent Developments and Agreements ......................................................................................... 1719
2003 Quantitative Settlement Agreement ............................................................................... 1820
2004 Arizona Water Settlements Act ....................................................................................... 1820
2007 Interim Guidelines/Coordinated Operations for Lake Powell and Lake Mead .............. 19
Pilot 21 System Conservation Program ................................................................................................ 22 20
Minute 319 and Minute 323 Agreements with Mexico ........................................................... 2122
2019 Drought Contingency Plans ........................................................................................... 2122
Upper Basin Drought Contingency Plan ........................................................................... 2123
Lower Basin Drought Contingency Plan .......................................................................... 23
500+ Plan24 2023 Draft Supplemental Environmental Impact Statement ................................................... 26 Issues for Congress ............................................................................. 25
Potential for Additional Curtailments ........................................... 33 Funding and Oversight of Existing Facilities and Programs ............................................ 26
Issues for Congress....... 33 Tribal Water Rights Settlements and Leasing ......................................................................... 35 New Facilities and Other Alterations ............................................... 26
Funding and Oversight of Existing Facilities and Programs ................................................... 26
Tribal Water Rights Settlements and Leasing 35 Post-2026 Operations/Agreements .......................................................................................... 27
Plans for New and Augmented Water Storage, Conveyance36 Concluding Observations ................................................... 27
Drought Contingency Plan Implementation and Future Basin Agreements ............................................. 28.............. 37

Figures
Figure 1. Colorado River Basin and U.S. Areas That Import Colorado River Water ...................... 32
Figure 2. Colorado River Basin Allocations .................................................................................... 7
Figure 3. Lake Powell and Lake Mead Elevations and Operational Tiers ..................................... 11
Figure 4. Colorado River Flows, Combined Storage at Lakes Mead and Powell, 1999-
2022 ....9 Figure 3. Colorado River Natural Flow at Lees Ferry, Arizona, with 10-Year Moving Average, 1906-2022 ............................................................................................. 18 Figure 4. Combined Storage at Lakes Mead and Powell, 1960-2022 ........................................... 1619 Congressional Research Service link to page 28 link to page 30 link to page 34 link to page 36 link to page 37 link to page 29 link to page 33 link to page 33 link to page 34 link to page 34 link to page 41
Figure 5. U.S. Lower Basin States: Intentionally Created Surplus Balance, 2010-2020 .............. 20
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Figure 65. Lake Powell End of -of-Month Elevation Projections ......................................................... 23 24
Figure 76. Lake Mead End of Month Elevation Projections ........................................................... 25

Tables
Table 1. Ten Tribes Study: Tribal Water Rights and Diversions .................................................... 15
Table 2. Lower Basin Water Delivery Curtailment Volumes Under Existing Agreements ........... 24

26 Figure 7. Modeled Lower Basin Shortages and Existing Contributions, 2023 Draft SEIS ........... 30 Figure 8. Lake Powell Projected Pool Elevations for 2023 SEIS Alternatives ............................. 32 Figure 9. Lake Mead Projected Pool Elevations for 2023 SEIS Alternatives ............................... 33 Tables Table 1. Lower Basin Water Delivery Curtailment Volumes Under Existing Agreements ........... 25 Table 2. Proposed New 2024 Lower Colorado River Basin State Water Curtailments in SEIS Action Alternatives ............................................................................................................ 29 Table 3. 2025-2026 Lower Colorado River Basin State Water Cuts in SEIS Action Alternatives ....................................................................................................... 30 Contacts
Author Information ........................................................................................................................ 2937

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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.River Basin covers more than 246,000 square miles.1 The river runs through The basin spans seven U.S. states (Wyoming, seven U.S. states (Wyoming,
Colorado, Utah, New Mexico, Arizona, Nevada, and California) and Colorado, Utah, New Mexico, Arizona, Nevada, and California) and Mexicotwo countries (the United States and Mexico). Pursuant to federal law, the . Pursuant to federal law, the
Bureau of Reclamation (ReclamationBureau of Reclamation (Reclamation), a component, part of the Department of the Interior of the Department of the Interior [DOI])(DOI), plays a prominent role plays a prominent role
in the management of the basin’s waters. In the Lower Basin (i.e., Arizona, Nevada, and California), in the management of the basin’s waters. In the Lower Basin (i.e., Arizona, Nevada, and California),
Reclamation also serves as Reclamation also serves as water master on behalf of the Secretary of the Interior, a role that elevates the on behalf of the Secretary of the Interior, a role that elevates the
status of the federal government in basin water management.status of the federal government in basin water management.21 The federal role in The federal role in the management of
managing Colorado River water is magnified by the multiple federally owned and operated water storage and 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 and hydropower suppliesconveyance facilities in the basin, which provide low-cost water and hydropower supplies to water users. .
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 majorityand recreation, among other uses. A majority (70%) of basin water supplies of basin water supplies (70%) are used to irrigate 5.5 million are used to irrigate 5.5 million
acres of land; basin waters also provide M&I water supplies to nearly 40 million people.acres of land; basin waters also provide M&I water supplies to nearly 40 million people.32 Much of the Much of the
area that depends on the river for area that depends on the river for its water supplies is outside of the drainage area for the Colorado River water supplies is outside of the drainage area for 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 CaliforniaDiego, and the Imperial Valley in Southern California (Figure 1). Colorado River hydropower facilities . Colorado River hydropower facilities
can provide up to 4,200 megawatts of electrical power per year.can provide up to 4,200 megawatts of electrical power per year.43 The river also provides habitat for a wide The river also provides habitat for a wide
range of species, including several range of species, including several federally endangered species. It flows through 7species listed under the federal Endangered Species Act (ESA; 87 Stat. 884, 16 U.S.C. §§1531-1544). It flows through seven national wildlife national wildlife
refuges and 11 National Park Service (NPS) units; these and other areas of the river support important refuges and 11 National Park Service (NPS) units; these and other areas of the river support important
recreational opportunities.5
Precipitation and runoff in the basin are highly variable. Water conditions on the river depend largely on
snowmelt in the basin’s northern areas. Observed historical data (1906-2020) show that overall, natural
flows in the Colorado River Basin averaged about 14.7 million acre-feet (MAF) annually.6 Flows have
dipped significantly during the current drought, which dates to 2000; natural flows from 2000 to 2020
averaged approximately 12.5 MAF per year.7 Reclamation has estimated that the 19-year period from
2000 to 2018 was the driest period in more than 100 years of record keeping.8 The dry conditions are
consistent with prior droughts in the basin that were identified through tree ring studies; some of these

1 J. C. Kammerer, “Largest Rivers in the United States,” USGS Fact Sheet, May 1990, at https://pubs.usgs.gov/of/1987/ofr87-
242/pdf/ofr87242.pdf.
2 As discussed in the section, recreational opportunities.4 1 As discussed later in “The Law of the River: Foundational Documents and Programs,”” the Boulder Canyon Project Act 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 of 1928 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 below 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 court 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 forms the basis for the designation Lower Basin water master. No similar authorities . No similar authorities and designationor designations have been provided for the have been provided for the
Upper Basin. Upper Basin.
32 U.S. Bureau of Reclamation 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. Hereinafter, Reclamation 2012 Supply/Demand Study.
4 Reclamation 2012 Supply/Demand Study, p. 3.
5 Reclamation 2012 Supply/ 3 Ibid., p. 3. 4 Ibid. Congressional Research Service 1 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, Colorado River Basin Water Supply and Demand StudyDemand Study, 2012. 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 2022, natural flows in the Colorado River Basin averaged about 14.6 million acre-feet (MAF) annually.5 Flows have dipped significantly during the 5 Reclamation, “PROVISIONAL Natural Flow Data 1906-2023 (Excel file, 0.3 MB) based on the April, 2023 24 MS,” at , p. 3.
6 U.S. Bureau of Reclamation, “Colorado River Basin Natural Flow and Salt Data-Current Natural Flow Data 1906-2022,” April
2022 24 Month Study, at https://www.usbr.gov/lc/region/g4000/NaturalFlow/provisional.html. Hereinafter, “1906-2020 Natural
Flows.”
7 1906-2020 Natural Flows.
8 U.S. Bureau of Reclamation, Annual Operating Plan for Colorado River Reservoirs, 2019, November 20, 2019, p. 8.
https://www.usbr.gov/lc/region/g4000/NaturalFlow/LFnatFlow1906-2023.2023.4.17.xlsx. Hereinafter, Reclamation, Congressional Research Service Congressional Research Service

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

droughts lasted for decades.9 Climate change impacts, including warmer temperatures and altered
precipitation patterns, may further increase the likelihood of prolonged drought in the basin.
Pursuant to the multiple compacts, federal laws, court decisions and decrees, contracts, and regulatory
guidelines governing Colorado River operations (collectively known as the Law of the River), Congress
and the federal government playcurrent drought, which dates to 2000; annual natural flows from 2000 to 2022 averaged approximately 12.1 MAF per year.6 Reclamation has noted that the 23-year period from 2000 to 2022 was the driest 23-year period in more than 100 years of 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 further increase the likelihood of prolonged drought in the basin.8 Congress plays a prominent role in the management of the Colorado River. Specifically, a prominent role in the management of the Colorado River. Specifically,
Congress funds and oversees Reclamation’s management of Colorado River Basin facilities, including Congress funds and oversees Reclamation’s management of Colorado River Basin facilities, including
facility operations and programs to protect and restore endangered facility operations and programs to protect and restore endangered and threatened species. Congress has also approved species. Congress has also approved
and continues to and continues to actively consider Indian water rights settlements involving Colorado River waters, and 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 development of new and expanded water storage in the basin. In addition, Congress has approved funding
supplemental funding to mitigate drought and stretch basin water suppliesto mitigate drought and stretch basin water supplies, and and has considered new authorities for Reclamation new authorities for Reclamation
to combat drought and enter into agreements with states and Colorado River contractors. to combat drought and enter into agreements with states and Colorado River contractors.
This report provides background on management of the Colorado River, with a focus on recent This report 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. developments. It also discusses the congressional role in the management of basin waters.

9 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 Drought in the Colorado River Basin,” Geophysical Research
Letters, vol. 49, no. 11 (June 2022), at https://doi.org/10.1029/2022GL098781.
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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, Colorado River Basin Water Supply and Demand Study, 2012.
The Law of the River:
Foundational Documents and Programs
The Law of the River: Foundational Documents and Programs The Law of the River 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 the Colorado River Basin began to recognize that 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 associated with development of the Colorado River. local interests alone could not solve the challenges associated with development of the Colorado River.
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Plans conceived by parties in California’s Imperial Valley to divert water from the mainstream of the Plans conceived by parties in California’s Imperial 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 Colorado River were thwarted because these proposals 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 States and Mexico.10 The river also presented engineering challenges, such as deep canyons and erratic
water flows, and economic hurdles that prevented local or state groups from building the necessary water flows, and economic hurdles that prevented local or state groups from building the necessary
storage facilities and canals to provide an adequate water supply. storage facilities and canals to provide an adequate water supply. BecauseIn part because local or state groups could not local or state groups could not
resolve these “national problems,” Congress considered resolve these “national problems,” Congress considered ideasoptions to control the Colorado River and resolve to control the Colorado River and resolve
potential conflicts between the states.11 potential conflicts between the states.11 Thus, inIn an effort to resolve these conflicts and an effort to resolve these conflicts and preventavoid litigation, litigation,
Congress gave its consent for the states and Reclamation to enter into an agreement to apportion Colorado Congress gave its consent for the states and Reclamation to enter into an agreement to apportion Colorado
River water supplies in 1921.12 River water supplies in 1921.12
The below sections discuss the resulting agreement, the Colorado River Compact “Reclamation Flow Data.” 6 Ibid. 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,” 87 Federal Register 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 Drought in the Colorado River Basin,” Geophysical Research Letters, 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,” Water Resources Research, 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 F.4th 794, 800 (9th Cir. 2022). 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 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 share. 12 Ch. 72, 42 Stat. 171 (1921). In lieu of litigation, interstate compacts have historically been a preferred means of allocating Congressional Research Service 3 link to page 9 Management of the Colorado River: Water Allocations, Drought, and the Federal Role The below sections discuss the resulting agreement, the Colorado River Compact, as well as key statutory authorities, the Supreme Court’s decision in Arizona v. California, and other documents , and other documents
and agreements that form the basis of the Law of the Riverand agreements that form the basis of the Law of the River, which governs Colorado River operations.13
. 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 was initially signed by all but one basin state (Arizona).signed by all but one basin state (Arizona).1413 Under the compact, the states established a framework Under the compact, the states established a framework
to apportion the water supplies between the Upper Basin and the Lower Basin, with the dividing line to apportion the water supplies between the Upper Basin and the Lower Basin, with the dividing line
between the two basins between the two basins located at Lee Ferry, AZ,at Lee Ferry, AZ,1514 below the confluence of the Colorado and Paria Rivers near below the confluence of the Colorado and Paria Rivers near
the Utah border.the Utah border.1615 Each basin was apportioned 7.5 MAF annually for beneficial consumptive use, and the 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 an additional 1 MAF 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 a total of 75 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 to make up for 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.low-flow years.17 The compact did not address inter- or intrastate allocations of water (which it left to The compact did not address inter- or intrastate allocations of water (which it left to
future agreements and legislation), nor did it address future agreements and legislation), nor did it address water to be made availabletribal rights or other rights that 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 to Mexico, the river’s
natural terminusnatural terminus; this matter was , the details of which were addressed in subsequent international agreements.addressed in subsequent international agreements.17 The compact was not The compact was not
to become binding until it had been approved by the legislatures of each of the signatory states and by to become binding until it had been approved by the legislatures of each of the signatory states and by
Congress.

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
the majority of the river’s runoff originates, feared that a storage facility making water available downstream might form a basis
for claims by Lower Basin states (California, Arizona, and Nevada) under prior appropriation doctrine before Upper Basin states
could develop means to access their share.
12 Ch. 72, 42 Stat. 171 (1921). In lieu of litigation, interstate compacts have historically been a preferred means of allocating
Congress. Boulder Canyon Project Act 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 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 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 (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 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 ratification of the compact by California and five other states (thereby allowing the compact to become water among competing uses. Pursuant to the U.S. Constitution, Article I, Section 10, Clause 3, no such compacts can be entered 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. into without the consent of Congress.
13 13 The Law of the River is the commonly used shorthand for the multiple compacts, federal laws, court decisions and decrees,
treaties, contracts, and regulatory guidelines collectively known under this heading.
14 Because the Colorado River Compact of 1922 did not specify the apportionments for individual states, Arizona initially refused 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 share of water. Arizona eventually signed and ratified the compact in 1944.signed and ratified the compact in 1944. See below section on “Arizona Ratification and
Arizona v. California Decision.”
15 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 upstream from that point, is the location of the USGS streamgage that has measured flows dating to 1921. After the compact waswa s
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.
1615 Arizona receives water under both the Upper and the Lower Basin apportionments, Arizona receives water under both the Upper and the Lower Basin apportionments, sincebecause 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; c.f. Boulder Canyon Project 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 section, “1944 U.S.-Mexico Water Treaty.” 18 BCPA, Ch. 42, 45 Stat. 1057 (1928), codified as amended at 43 U.S.C. §617. Congressional Research Service 4 link to page 26 link to page 26 Management of the Colorado River: Water Allocations, Drought, and the Federal Role effective without Arizona’s concurrence), and California agreeing by act of its legislature to limit its water 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 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 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 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 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 agreements between the United States and Mexico, known as minutes, regarding matters related to the treaty’s execution and interpretation.22 Arizona v. California Arizona ratified the Colorado River Compact in parts of the state are in both basins.
17 As a result, in some years in which Lake Powell inflows are less than 7.5 MAF, less than 7.5 MAF may be available to Lower
Basin states.
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Boulder Canyon Project Act
Congress approved and modified the Colorado River Compact in the Boulder Canyon Project Act (BCPA)
of 1928.18 The act ratified the 1922 compact, authorized the construction of a federal facility to impound
water in the Lower Basin (Boulder Dam, later renamed Hoover Dam) and related facilities to deliver
water in Southern California (e.g., the All-American Canal, which delivers Colorado River water to
California’s Imperial Valley), and apportioned the Lower Basin’s 7.5 MAF per year among the three
Lower Basin states. It provided 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 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.
Congress’s approval of the compact in the BCPA was conditioned on a number of factors, including
ratification 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 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, 1929.19
Arizona Ratification and Arizona v. California Decision
Arizona did not ratify the Colorado River Compact until 1944, at which time the state began to pursue a 1944, at which time the state began to pursue a
federal federal project (later named the Central Arizona Project, or CAP) project to bring Colorado River water to its primary population centers in Phoenix and Tucson. to bring Colorado River water to its primary population centers in Phoenix and Tucson.
California opposed the project, arguing that under the doctrine of prior appropriation,20 California’s
historical use of the river trumped Arizona’s rights to the Arizona allotment.21 California also argued that
Colorado River apportionments under the BCPA included water developed on Colorado River tributaries,
whereas Arizona claimed, among other things, that these apportionments included the river’s mainstream
waters only.
In 1952, Arizona filed suit in the U.S. Supreme Court to settle the issue. 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 from Colorado River tributaries 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 and other issues.24 Eleven years later, in the 1963 Eleven years later, in the 1963
Arizona v. California decision,decision,22 the Supreme Court ruled in favor of Arizona, finding that Congress had
intended to apportion the mainstream of the Colorado River and that California and Arizona each would
receive one-half of surplus flows.23 The same Supreme Court decision held that Section 5 of the BCPA
controlled the apportionment of waters among Lower Basin States, and that the BCPA (and not the law of
prior appropriation) controlled the apportionment of water among Lower Basin states.24 The ruling was
notable for its directive to forgo traditional Reclamation deference to state law under the Reclamation Act
of 1902, and formed the basis for the Secretary of the Interior’s unique role as water master for the Lower

18 Boulder Canyon Project Act (BCPA), Ch. 42, 45 Stat. 1057 (1928), codified as amended at 43 U.S.C. 617.
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
“surplus” years in the California Seven-Party Agreement, signed in August 1931.
20 Historically, water in the western United States the Supreme Court ruled in favor of Arizona.25 The ruling was notable in forgoing typical Reclamation deference to state law under 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 “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 Report R42917, Mexico: Background and U.S. Relations, 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 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 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 & Water Commission, Minutes between the United States and Mexican Sections of the IBWC, 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 of the has been governed by some form of the rule of prior appropriation. Under this . Under this
rule, the party that first appropriates water and puts it to rule, the party that first appropriates water and puts it to beneficial use thereby acquires a vested right to continue to divert and thereby acquires a vested right to continue to divert and
use that quantity of water against claimants junior in time.use that quantity of water against claimants junior in time.
21 Under the BCPA, Arizona and California also were to divide any excess, or surplus, supplies (i.e., amounts exceeding the 7.5
MAF basic apportionment). What was meant by the term surplus—and how much water California could claim under this
authority—was significant to the arguments in the case.
22 Arizona v. California, 373 U.S. 546 (1963).
23 Id. at 546, 573.
24 Id. at 585-586. This decision gave the Secretary the power to apportion surpluses and shortages among and within Lower Basin
states.
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Basin.25 The decision also held that Native American reservations on the Colorado River were entitled to
priority under the BCPA.26 Later decrees by the Supreme Court in 1964 and 1979 supplemented the 1963
decision.27
Following the Arizona v. California decision, Congress eventually authorized Arizona’s conveyance
project for Colorado River water, the Central Arizona Project (CAP), in the Colorado River Basin Project
Act of 1968 (CRBPA).28 As a condition for California’s support of the project, Arizona agreed that, in the
event of shortage conditions, California’s 4.4 MAF has priority over CAP water supplies.
1944 U.S.-Mexico Water Treaty29
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.30 The treaty established water allocations
for the two countries and created a governance framework (the International Boundary and Water
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
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
agreements between the United States and Mexico, known as minutes, regarding matters related to the
treaty’s execution and interpretation.31
Upper Basin Compact and Colorado River Storage Project Authorizations
Projects originally authorized for study in the Upper Basin under BCPA were not allowed to move
forward until the Upper Basin states determined their individual water allocations, which they did under
the Upper Colorado River Basin Compact of 1948. The Upper Basin Compact established Colorado
(where the largest share of runoff to the river originates) as the largest entitlement holder in the 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 Wyoming

25 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 that 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 are more akin to trial court judgments than the Supreme Court’s usual appellate decisions. 25 The 1963 Supreme Court decision in Arizona v. California 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) (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); cf. California v. United States, 438 U.S. 645 (1978). Congressional Research Service 5 Management of the Colorado River: Water Allocations, Drought, and the Federal Role Reclamation Act of 1902 and formed the basis for the Secretary of the Interior’s role as water master for 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 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. 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 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 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 toward its allocation in the Colorado River Compact and BCPA. The Supreme Court concluded that 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, are governed under separate authorities.30 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 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 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 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 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 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 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. California noted that the 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 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. 27 Ibid. at 564–65. 28 Ibid. at 593. 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. California also addressed 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. at 593-594. As the court explained, BCPA §5 serves as the basis for DOI’s authority to apportion Lower Basin water deliveries. 32 Ibid. 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 best interests of the Basin States, and the welfare of the Nation”). 33 Ibid. at 592–93. 34 Ibid. 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 generally apply unless Congress explicitly provides otherwise); c.f. BCPA, supra note 19. Congressional Research Service 6 link to page 14 link to page 14 link to page 20 Management of the Colorado River: Water Allocations, Drought, and the Federal Role In 1964, the Supreme Court issued a decree implementing its opinion in Arizona v. California.35 The 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 In the event flows are insufficient to provide 7.5 MAF per year to the Lower Basin, the decree instructs DOI to account for present perfected rights (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 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 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, 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 Arizona v. California continues to play a significant role in Colorado River allocations. Multiple federal statutes pertaining to Colorado River basin management refer to the Arizona v. California decree and 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. 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 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 forward with federally funded construction until the Upper Basin states determined their individual water 35 Arizona v. California, 376 U.S. 340“the Secretary of the Interior, in carrying out
provisions of the Act, shall proceed in conformance with such laws.”
26 Indian reserved water rights were first recognized by the Supreme Court in Winters v. United States in 1908. Winters v. United
States, 207 U.S. 564, 575-77 (1908). Under the Winters 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 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 settlements, see below
section on “Tribal Water Rights” and CRS Report R44148, Indian Water Rights Settlements, by Charles V. Stern.
27 Arizona v. California, 376 U.S. 340, 341 (1964). The 1964 decree determined, among other things, that all water in the (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 mainstream 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 States” and that the Secretary would release water under only three types of designations for a year: “normal, surplus, and
shortage.”shortage.” The 1979 supplemental decree determined the 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. See supra note 26. Among other things, the decrees set forth tribal water rights and present perfected rights of various parties in the Lower Basin.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 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 accordance with state law and exercised by actually diverting a specific quantity of water and/or reservation of water rights for federal use. Ibid. at 154. 39 Arizona v. California. 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 Winters 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 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 settlements, see below section, “Tribal Water Rights” 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.” Ibid. at 155. 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. 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 1873-1903, and an additional 0.04 MAF from other uses. 42 See, for example, 43 U.S.C. §§1521, 1525. Congressional Research Service 7 link to page 13 Management of the Colorado River: Water Allocations, Drought, and the Federal Role allocations, which occurred under the Upper Colorado River Basin Compact of 1948.43 Because there was 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: 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 to the Lower Basin have been met. Other states also received percentage-based allocations, including Wyoming (14%), New Mexico (11.25%), and Utah (23%).
28 Colorado River Basin Project Act of 1968, P.L. 90-537.
29 For more information on the 1994 U.S.-Mexico Water Treaty and Colorado River water sharing issues with Mexico, see CRS
Report R45430, Sharing the Colorado River and the Rio Grande: Cooperation and Conflict with Mexico.
30 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
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.
31 The complete list of minutes is available at https://www.ibwc.gov/Treaties_Minutes/Minutes.html. For more information on
recent minutes, see section, “Minute 319 and Minute 323 Agreements with Mexico.”
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Management of the Colorado River: Water Allocations, Drought, and the Federal Role

(14%), New Mexico (11.25%), and Utah (23%).32 Arizona was allocated 50,000 AF in addition to its Arizona was allocated 50,000 AF in addition to its
Lower Basin apportionment, in recognition of the Lower Basin apportionment, in recognition of the small portion of the state in the Upper Basinportion of the state in the Upper 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.of the Upper Basin Compact.3344 43 Upper Colorado River Basin Compact, 1948. 44 For more information, see Upper Colorado River Commission, “About the UCRC,” at http://www.ucrcommission.com/about-us/. Congressional Research Service 8 Management of the Colorado River: Water Allocations, Drought, and the Federal Role
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.

32 ThereNotes: 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 was uncertainty about how much water would remain in the Upper Basin after Colorado River Compact obligations to
Lower Basin states were Lower Basin states were fulfilled. fulfil ed. Therefore, outside of 50,000 AF provided annually to Arizona, the Upper Basin Compact 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.includes apportionments in terms of percentage of the overall Upper Basin allocation.
33 For more information, see Upper Colorado River Commission, “About the UCRC,” at http://www.ucrcommission.com/about-
us/.
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7 Subsequent federal legislation paved the way for development of Upper Basin waters. The Colorado River Storage Project (CRSP) Act of 1956 authorized CRSP initial units of Glen Canyon, Flaming Gorge, 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 project’s costs of operation, maintenance, and emergency expenditures. Congressional Research Service 9

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Notes: 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 fulfil ed.
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.
Subsequent federal legislation paved the way for development of Upper Basin allocations. The Colorado
River Storage Project (CRSP) Act of 1956 authorized storage reservoirs and dams in the Upper Basin,
including the Glen Canyon, Flaming Gorge, Navajo, and Curecanti Dams. 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 project’s costs of operation, maintenance, and emergency
expenditures.
In addition to the aforementioned authorization of CAP in Arizona, the 1968 CRBPA amended CRSP to
authorize several other Upper Basin projects (e.g., the Animas La Plata and Central Utah projects) as
CRSP participating projects. It also directed that the Secretary of the Interior propose operational criteria
for Colorado River Storage Project units (including the releases of water from Lake Powell) that prioritize
Colorado River Basin Project Act of 1968 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 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 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 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 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 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 certain California and Nevada users whose water rights predate the CAP, consistent with the 1964 Arizona v. California decree.48 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 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 operational criteria—known as Long-Range Operating Criteria (LROC)—for federally authorized 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 (1) treaty obligations to Mexico, (2) the Colorado River Compact requirement for the Upper Basin to not
deplete more than 75 MAF to Lower 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 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 first adopted LROC in 1970; they were last modified in 2005.52 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 River Basin Project Act (CRBPA) were codified as amendments to the CRSPA. Ibid. §§620a, 620a-1. 46 Ibid. 47 43 U.S.C. §1521. 48 See 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 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 Supreme Court decree, 376 U.S. 340, which is associated with the 1963 opinion Section III, Apportionment and Contracts in Time of Shortage, 373 U.S. 546, 592-94. See also 43 U.S.C. §1521(b) (allowing modifications to Central Arizona Project diversions). 49 Ibid. §§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 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 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 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). 51 Ibid. 52 Operating Criteria, 70 Federal Register 15,873 (Mar. 29, 2005); Colorado River Reservoirs, Coordinated Long-Range Operations, 35 Federal Register 8951 (June 10, 1970). Through later legislation, Congress required that, in preparing the LROC Congressional Research Service 10 Management of the Colorado River: Water Allocations, Drought, and the Federal Role Water Storage and Operations The Colorado River Basin’s large water storage projects canBasin states over any 10-year period (i.e., 7.5 MAF per year), and
(3) carryover storage to meet these needs. The CRBPA also established the Upper Colorado River Basin
Fund and the Lower Colorado River Basin Development Fund, both of which were authorized to utilize
revenues from power generation from relevant Upper and Lower Basin facilities to fund certain expenses
in the sub-basins.34
Water Storage and Operations
Due to the basin’s large water storage projects, water users are able to store as much as 60 MAF, or about store as much as 60 MAF, or about
four times the Colorado River’s annual flowsfour times the Colorado River’s annual flows, to insulate water users from annual variability in flows. Thus, storage and operations in the basin receive . Thus, storage and operations in the basin receive
considerable attention, particularly at the basin’s two largest dams and their storage reservoirs: Glen 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 storage capacity) and Hoover Dam/Lake 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 status of these projects is Mead in the Lower Basin (26.1 MAF of storage capacity). The status of these projects is of interest to
basin stakeholders and observers and is monitored closely by Reclamation.
Glen Canyon Dam, completed in 1963monitored closely by Reclamation and interested stakeholders as an indicator of basin health. 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 , serves as the linchpin for Upper Basin storage and regulates flows
from the Upper Basin to the Lower Basin, pursuant to the Colorado River Compact. from the Upper Basin to the Lower Basin, pursuant to the Colorado River Compact. It also generates
approximately 3,640 gigawatt hours (GWhFrom 2000 to 2020, it generated an average of approximately 3.8 billion kilowatt-hours (KWh) of electricity per year, which the Western Area Power ) of electricity per year, which the Western Area Power
Administration (WAPA) supplies to 5.8 million customers in Upper Basin States.Administration (WAPA) supplies to 5.8 million customers in Upper Basin States.3553 Other significant Other significant
storage in the Upper Basin includes the initial storage in the Upper Basin includes the initial “units”units of the CRSP: the Aspinall Unit in Colorado of the CRSP: the Aspinall Unit in Colorado
(including Blue Mesa, Crystal, and Morrow Point dams on the Gunnison River, with combined storage (including Blue Mesa, Crystal, and Morrow Point dams on the Gunnison River, with combined storage
capacity of more than 1 MAF),capacity of more than 1 MAF),3654 the Flaming Gorge Unit in Utah (including Flaming Gorge Dam on the the Flaming Gorge Unit in Utah (including Flaming Gorge Dam on the
Green River, with a capacity of 3.Green River, with a capacity of 3.78 8 MAF), and the Navajo Unit in New Mexico (including Navajo Dam MAF), and the Navajo Unit in New Mexico (including Navajo Dam
on the San Juan River, with a on the San Juan River, with a capacity of 1 MAF). The Upper Basin is also home to 16 participating capacity of 1 MAF). The Upper Basin is also home to 16 participating

34 Basin-wide operational commitments on the Colorado River were established in the 1970 Criteria for Coordinated Long-Range
Operation of Colorado River Reservoirs, which coordinated the operation of reservoirs in the Upper and Lower Basins, including
releases from Lake Powell and Lake Mead. These operating instructions have been modified by more recent operational
agreements intended to mitigate the effects of long-term drought.
35 Western Area Power Administration, CRSP MC at a Glance, FY2020,” at https://www.wapa.gov/newsroom/FactSheets/
Documents/CRSP-at-a-glance.pdf..
36 The Curecanti Unit was renamed the Aspinall Unit in 1980 in honor of U.S. Representative Wayne N. Aspinall of Colorado.
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projects, which are authorized to use water for irrigation, projects, which are authorized to use water for irrigation, municipal and industrialM&I uses, and other uses, and other
purposes.purposes.37
In the Lower Basin, 55 Hoover Dam, completed in 1936, provides the majority of the Lower Basin’s storage Hoover Dam, completed in 1936, provides the majority of the Lower Basin’s storage
and generatesand generates on average about 4 billion KWh of electricity per year for customers in California, Arizona, and about 4 billion KWh of electricity per year for customers in California, Arizona, and
Nevada.Nevada.38 56 Also important for Lower Basin Operations are Davis Dam/Lake Mohave, which regulates 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 flows to 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 diversion into the Colorado River Aqueduct (thereby allowing for deliveries to urban areas in southern
Southern California) and CAP (allowing for diversion to users in Arizona). Further downstream on the California) and CAP (allowing for diversion to users in Arizona). Further downstream on the
Arizona/California border, Imperial Dam (a diversion dam) diverts Colorado River water to the All-Arizona/California border, Imperial Dam (a diversion dam) diverts Colorado River water to the All-
American Canal for useAmerican Canal for use in some of the river’s largest agricultural areas in California’s Imperial and Coachella Valleys. 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).).3957 The studies take into account forecasted hydrology, reservoir and 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. 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 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. 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, 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/index.html. 56 Reclamation, “Hoover Dam Frequently Asked Questions and Answers,” at https://www.usbr.gov/lc/hooverdam/faqs/powerfaq.html, accessed August 3, 2022. 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/ Congressional Research Service 11 link to page 25 link to page 23 link to page 23 link to page 29 Management of the Colorado River: Water Allocations, Drought, and the Federal Role 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
(ft) above mean sea level. above mean sea level.
In addition to the 24-month studies, the CRBPA requires the Secretary In addition to the 24-month studies, the CRBPA requires the Secretary of the Interior to transmit to Congress and the to transmit to Congress and the
governors of the basin states, by January 1 of each year, governors of the basin states, by January 1 of each year, a report describingan Annual Operating Plan (AOP). In the AOP, Reclamation describes the actual operation for the the actual operation for the
preceding water year and the projected operation for the coming yearpreceding water year and the projected operation for the coming year. This report is commonly referred to
as the annual operating plan (AOP). The AOP’s projected January 1 water conditions for the upcoming . The AOP’s projected January 1 water conditions for the upcoming
calendar year establish a baseline for future annual operations.calendar year establish a baseline for future annual operations.4058
Since the adoption of Since the adoption of new operational guidelines by Reclamation and basin states in 2007 (see below operational guidelines by Reclamation and basin states in 2007 (see below
section, section, “2007 Interim Guidelines”),), Reclamation has tied operations of operations of the Hoover and Glen Canyon DamsHoover and Glen Canyon Dams have been tied to to
specific pool elevations at Lake Mead and Lake Powellspecific pool elevations at Lake Mead and Lake Powell (Figure 3). For Lake Mead, the first level of . For Lake Mead, the first level of
shortage (a shortage (a Level Tier One Shortage Condition) in the 2007 guidelines, under which Arizona) in the 2007 guidelines, under which Arizona’s and Nevada’s and Nevada’s
allocations are allocations are decreasedcurtailments (along with releases to Mexico), is triggered if (along with releases to Mexico), is triggered if the Lake Mead Lake Mead pool elevation falls below 1,075 falls below 1,075
feet. For Lake Powell, releases under tiered operations are based on storage levels in both Lake Powell 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 2019, and Lake Mead. Drought contingency plans (DCPs) for the Upper and Lower Basins, enacted in 2019,
overlaid additional overlaid additional efforts that tied operational changes operational changes tied to elevations in both reservoirs. For Lake Mead, to elevations in both reservoirs. For Lake Mead,
this included additional this included additional triggers for curtailments beyond those established in 2007.curtailments beyond those established in 2007.4159 For Lake Powell, the For Lake Powell, the
Upper Basin DCP incorporated a Drought Response Operations Agreement (DROA) that established a Upper Basin DCP incorporated a Drought Response Operations Agreement (DROA) that established a
target lake elevation of 3,525 feettarget lake elevation of 3,525 feet and. It also provided for altered releases from Glen Canyon Dam and Upper provided for altered releases from Glen Canyon Dam and Upper
Basin reservoirs Basin reservoirs in order to protect Lake Powell from falling below an elevation that would no longer produce to protect Lake Powell from falling below an elevation that would no longer produce

37 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 one project—the Pine River Extension Project—had its authorization
deleted by Congress.) For a complete list of projects, see https://www.usbr.gov/uc/rm/crsp/index.html.
38 Bureau of Reclamation, “Hoover Dam Frequently Asked Questions and Answers,” at https://www.usbr.gov/lc/hooverdam/faqs/
powerfaq.html, accessed August 3, 2022.
39 Current 24-month studies, as well as two- and five-year probable projections of Lake Mead and Powell elevations, are
available at Bureau of Reclamation, “Colorado River System Projections Overview,” https://www.usbr.gov/lc/region/g4000/
riverops/coriver-projections.html.
40 Current and historical AOPs are available at Bureau of Reclamation, “Annual Operating Plan for Colorado River Reservoirs,”
https://www.usbr.gov/uc/water/rsvrs/ops/aop/.
41hydropower. These efforts are discussed more in the below section “Recent Developments and Agreements.” Recent Conditions Falling water levels in Lake Mead have resulted in Reclamation announcing Lower Colorado River Basin delivery 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 delivery cutbacks.61 In March 2022, Lake Powell fell below the target elevation of 3,525 feet, which had not occurred since the late 1960s.62 coriver-projections.html. 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/. 59 For example, a new set of curtailments for Nevada and Arizona at lake elevations up to 1,090 feet ( For example, a new set of curtailments for Nevada and Arizona at lake elevations up to 1,090 feet (Tier Zero) was added ) was added
pursuant to the 2019 DCP for the Lower Colorado River Basin.pursuant to the 2019 DCP for the Lower Colorado River Basin.
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hydropower. These efforts are discussed more in the below section ““Recent Developments and
Agreements”.”
Recent Conditions
Based on low water storage levels in 2021 and 2022, Reclamation announced Lower Colorado River
Basin delivery curtailments for Arizona and Nevada, in accordance with previous plans. In August 2021,
Reclamation declared the first-ever Level One Shortage Condition for the Lower Basin.42 In August 2022,
Reclamation announced the first-ever Level Two Shortage, which resulted in additional water supply
delivery cutbacks.43 In March 2022, Lake Powell fell below the target elevation of 3,525 feet for the first
time since the late 1960s.44

42 Bureau of 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 Operating Conditions for Lake Powell and Lake Mead,” press release, 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.August 16, 2021, at https://www.usbr.gov/newsroom/#/news-release/3950. Hereinafter, Reclamation, August 2021 press release.
43 Bureau of 61 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,” press release, August 16, 2022, at https://www.usbr.gov/newsroom/news-release/Conditions for Lake Powell and Lake Mead,” press release, August 16, 2022, at https://www.usbr.gov/newsroom/news-release/
4294. 4294.
44 Bureau of62 Reclamation, “Lake Powell to Temporarily Decline Below 3,525 Feet,” press release, March 4, 2022, at 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, 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 power production would cease. or the level at which power production would cease.
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Figure 3. Lake Powell and Lake Mead Elevations and Operational Tiers
(as of January 2022)

Source: Figure by CRS, based on Bureau of Reclamation 24-month study data (https://www.usbr.gov/uc/water/crsp/
studies/) and information in the 2007 Interim Guidelines and the 2019 Drought Contingency Plan for the Lower Basin.
Notes: DROA= Upper Colorado River Basin Drought Response Operations Agreement. Depicts January 1 elevations for
each year.
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 §§4321 et seq.) and the Endangered Species Act (ESA; 87 Stat. 884, 16 U.S.C. §§1531-1544)) and the ESA. Thus, . Thus,
many of the environmental impacts associated with the development of basin resources were not 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 to mitigate these effects. 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 particular, salinity control) 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 the effects of facility operations on endangered and threatened species. species.
Salinity Control
Salinity and water quality are Salinity and water quality are longstandinglong-standing issues in the Colorado River Basin. Parts of the Upper Basin issues in the Colorado River Basin. Parts of the Upper Basin
are covered by salt-bearing shale (which increases salt content are covered by salt-bearing shale (which increases salt content inof water inflows), and salinity content water inflows), and salinity content
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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. Colorado River Basin. However, afterAfter years of dispute between the United States and Mexico regarding 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, the salinity 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.1973, with the signing of Minute 242 of the International Boundary and Water Commission.4563 The The
agreement guarantees Mexico that the average salinity of its treaty deliveries will be no more than 115 agreement guarantees Mexico that the average salinity of its treaty deliveries will be no more than 115
parts per million higher than the parts per million higher than the saltsalinity content of the water diverted to the All-American Canal at Imperial 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 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 (agreement, Congress passed the Colorado River Basin Salinity Control Act of 1974 (P.L. 93-320), which ), which
authorized desalting and salinity control facilities to improve Colorado River water quality. The most 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 prominent of these facilities is the Yuma Desalting Plant, which was largely completed in 1992 but has
never operated at never operated at capacity.46capacity due to cost and other factors.64 In 1974, the seven basin states also established water quality standards for In 1974, the seven basin states also established water quality standards for
salinity through the Colorado River Basin Salinity Control Forum.salinity through the Colorado River Basin Salinity Control Forum.4765
Endangered Species Efforts and Habitat Improvements
Congress enacted the ESA in 1973.Congress enacted the ESA in 1973.4866 As the federal government listed some basin species under ESA in As the federal government listed some basin species under ESA in
accordance with the act,accordance with the act,4967 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 endangered fish species
on 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
of four species of endangered fish in the Upper Colorado River Basin.50 Congress authorized this program
in P.L. 106-392. The program is implemented through several stakeholders under a cooperative agreement
signed by the governors of Colorado, Utah, and Wyoming; DOI; 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 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. Reclamation is the lead federal

45 63 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.
4664 The Yuma Desalting Plant’s limited operations have been due in part to the cost of its operations (desalination can require 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 yearsconsiderable electricity to operate) and surplus flows in the Colorado River during some years compared to what was expected.
. In lieu of operating the plant, high-salinity irrigation water has been separated from the United States’ required deliveries to 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 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 operatedthe Gulf of California. Whether and how the plant should be operated, and how the impacts on the Ciénega de Santa Clara from and how the impacts on the Ciénega de Santa Clara from
the untreated irrigation runoff should be managedthe untreated irrigation runoff should be managed, remain topics of some debate in the basin and between Mexico and the United remain topics of some debate in the basin and between Mexico and the United
States. States.
4765 Additional information about the forum and related salinity control efforts is available at Colorado River Basin, Additional information about the forum and related salinity control efforts is available at Colorado River Basin, “Salinity Salinity
Control Forum,Control Forum,” at https://www.coloradoriversalinity.org/. at https://www.coloradoriversalinity.org/.
4866 For background information on the Endangered Species Act For background information on the Endangered Species Act (87 Stat. 884, 16 U.S.C. §§1531-1544), see CRS Report R46677, , see CRS Report R46677, The Endangered Species Act: Overview
and Implementation. .
4967 Several Several endangeredlisted species are found throughout the Colorado River Basin. Some are specifically found in the Colorado River, species are found throughout the Colorado River Basin. Some are specifically found in the Colorado River,
such as the Razorback sucker (such as the Razorback sucker (Xyrauchen texanus), Bonytail chub (), Bonytail chub (Gila elegans), Colorado pikeminnow (), Colorado pikeminnow (Ptychocheilus Lucius), ),
and Humpback chub (and Humpback chub (Gila cypha). ).
50 For more information, see Upper Colorado River Endangered Fish Recovery Program at
http://www.coloradoriverrecovery.org/ucConsultation about an agency action’s effects on these species is required by 16 U.S.C. §1536(a). .
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1213 Management of the Colorado River: Water Allocations, Drought, and the Federal Role 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. Upper Colorado Endangered Fish Recovery Program 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.68 Congress formally authorized this program in 2000.69 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 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 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. Reclamation is the lead federal

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agency for the program and provides the majority of federal funds for implementation. agency for the program and provides the majority of federal funds for implementation. It is also funded
throughOther funding includes a portion of Upper Basin hydropower revenues from WAPA a portion of Upper Basin hydropower revenues from WAPA; and funding from FWS; the states of Colorado, FWS; the states of Colorado,
Wyoming, and Utah; and water users, among others. 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 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.recovery of ESA-listed fish species on the San Juan River, the Colorado’s largest tributary.5170 The program The program
is a partnership implemented under a cooperative agreement between is a partnership implemented under a cooperative agreement between the Department of the InteriorDOI and and
the states of Colorado and New Mexico, the Jicarilla Apache Nation, the Navajo Nation, the Southern Ute 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.Indian Tribe, and the Ute Mountain Ute Indian Tribe.5271 It is concerned with the recovery of the Razorback It is concerned with the recovery of the Razorback
sucker (sucker (Xyrauchen texanus) and Colorado pikeminnow () and Colorado pikeminnow (Ptychocheilus Lucius). Congress authorized this ). Congress authorized this
program in program in P.L. 106-392 with the aim to protect the genetic integrity and population of listed species, 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 conserve and restore habitat (including water quality), reduce nonnative species, and monitor species. The
Recovery Programprogram is coordinated by is coordinated by FWS.FWS, and Reclamation is responsible for operating the Animas-La Plata 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 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 program is funded by a portion of revenues from power generation, Reclamation, participating states, and
hydropower revenues from WAPA in the Upper Basin, Reclamation, the Bureau of Indian Affairsthe Bureau of Indian Affairs, and participating states. Recovery efforts for listed fish are coordinated with the Upper . Recovery efforts for listed fish are coordinated with the Upper Colorado Endangered Fish Recovery ProgramColorado
River Program discussed above. .
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 (from Congress under the Grand Canyon Protection Act of 1992 (P.L. 102-575) to operate Glen Canyon ) to operate Glen Canyon
Dam “in such a manner as to protect, mitigate adverse impacts to, and improve the values for which Dam “in such a 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.”Grand Canyon National Park and Glen Canyon National Recreation Area were established.”5372 This This
program uses experiments to determine how water flows affect natural resources south of the dam. program uses 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 Reclamation is in charge of modifying flows for experiments, and the U.S. Geological Survey conducts
monitoring and other studies to evaluate the effects of the flows.54 The results are expected to better
inform managers how to provide water deliveries and conserve species. The majority of program funding
comes from hydropower revenues generated at Glen Canyon Dam.
Lower Colorado Multi-Species Conservation Program
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
farmers, tribes, industries, and urban residents.55 The MSCP began in 2005 and is planned to last for at
least 50 years.56 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

51monitoring and 68 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. 69 P.L. 106-392. 70 For more information, see U.S. Fish and Wildlife Service, “San Juan River Basin Recovery Implementation Program,” For more information, see U.S. Fish and Wildlife Service, “San Juan River Basin Recovery Implementation Program,”
at https://www.fws.gov/southwest/sjrip/. https://www.fws.gov/southwest/sjrip/.
5271 It also includes participation by water development interests in Colorado and New Mexico. It also includes participation by water development interests in Colorado and New Mexico.
5372 For more information, see For more information, see Bureau of Reclamation, Glen Canyon Dam Adaptive Management Program, “Glen Canyon Dam Reclamation, Glen Canyon Dam Adaptive Management Program, “Glen Canyon Dam
High Flow Experimental Release,” at https://www.usbr.gov/uc/progact/amp/ltemp.html. High Flow Experimental Release,” at https://www.usbr.gov/uc/progact/amp/ltemp.html.
54 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.
55 The stakeholders include six federal and state agencies, six 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
Colorado River Multi-Species Conservation Program at https://www.lcrmscp.gov/.
56 The program was formally authorized by Congress under Subtitle E of Title IX of P.L. 111-11.
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Congressional Research Service 14 Management of the Colorado River: Water Allocations, Drought, and the Federal Role other studies to evaluate the effects of the flows.73 The results are expected to better inform managers how 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 (8 listed under ESA) along the Lower Colorado River while maintaining water and power supplies for farmers, tribes, industries, and urban residents.74 The MSCP began in 2005 and is planned to last for at least 50 years.75 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 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 biological opinion (BiOp) issued by the FWS in 1997 served as a basis for the program. Modifications to
the 1997 BiOp were made in 2002, and in 2005, the BiOp was renewed for 50 years. Nonfederal entities
received an incidental take permit under Section 10(a) of the ESA for their activities in 2005 and shortly
thereafter implemented a habitat conservation plan.
covers operations and maintenance activities 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 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 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 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 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 split evenly between Reclamation (50%) and the states of California, Nevada, and Arizona (who
collectively fund the remaining 50%).collectively fund the remaining 50%).57 The management and implementation of the MSCP is the
responsibility of Reclamation, in consultation with a steering committee of stakeholders.
The management and implementation of the MSCP is the responsibility of Reclamation, in consultation with a steering committee of stakeholders. 73 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. 74 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 Colorado River Multi-Species Conservation Program at https://www.lcrmscp.gov/. 75 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 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 15 Management of the Colorado River: Water Allocations, Drought, and the Federal Role 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 Colorado River Dam fundFund uses power revenues generated by the Boulder Canyon Project (i.e., Hoover Dam) to 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, col ects revenues from the Central Arizona Project (CAP), as Development Fund, col ects revenues from the Central Arizona Project (CAP), as well aswel as from a surcharge on revenues from the a surcharge on revenues from the
Boulder Canyon and Parker-Davis Projects that was enacted under the Hoover Power Plant Act of 1984 (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, salinity 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 of 2004 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 others). In the (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 col ects revenues from the initial units of the Colorado River Storage Upper Basin, the Upper Colorado River Basin Fund col ects revenues from the initial units of the Colorado River Storage
Project and funds operation and maintenance expenses, salinity control, the Glen Canyon Dam Adaptive Management 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. Program, and endangered fish studies on the Colorado and San Juan rivers, among other things.
Tribal Water Rights
Twenty-twoSource: 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.80 Tribal water diversions based on these rights typically come out of individual state allocations. There are 30 federally recognized tribes in the Colorado River Basin federally recognized tribes in the Colorado River Basin have quantified water diversion
rights that have been confirmed by court decree or final settlement; these rights typically come out of
existing state allocations. These tribes collectively possess rights to 2.9, many of whom have settled or unresolved (i.e., currently claimed for use but unsettled) tribal water rights.81 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 unknown.82 According to Reclamation, as of December 2020, tribes held diversion rights to approximately 3.4 MAF per year of Colorado River MAF per year of Colorado River
water.58 As of 2015, these tribes typicallywater.83 Previous studies noted that these tribes were using just over half of their quantified rights. were using just over half of their quantified rights.59
Additionally, 13 other basin tribes have reserved water rights claims that have yet to be resolved, although
the total potential amount of these claims has not been estimated.60 Increased84 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 water use by tribes with
existingexisting quantified and settled water rights, and/or future settlement of claims and additional consumptive use of basin waters water rights, and/or future settlement of claims and additional consumptive use of basin waters
by by other tribes, is likely to exacerbate the 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 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, see CRS Report R44148, Indian Water Rights Settlements. 81 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 16 link to page 22 link to page 23 link to page 23 link to page 38 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 other viable alternative sources of water.85 Drought and the Supply/Demand Imbalance 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.86 As noted, from 1906 to 2022, observed competition for basin water resources.
The potential for increased use of tribal water rights (which, once ratified, are counted toward state-
specific allocations where the tribal reservation is located) has been studied in recent years. In 2014,

57 As of the end of 2021, more than $381 million had been spent on program implementation. Lower Colorado River Multi-
Species Conservation Program, “Implementation and Funding,” at https://www.lcrmscp.gov/about_us/
implementation_and_funding. Accessed August 3, 2022.
58 Reclamation 2012 Supply/Demand Study, Technical Report C, Appendix C9, p. C9-4.
59 Colorado River Research Group, Tribes and Water in the Colorado River Basin, June 2016, at https://www.usu.edu/colorado-
river-research-group/files/crrg_tribal_water_rights.pdf. 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 diversion rights.
60 Colorado River Research Group, Tribes and Water in the Colorado River Basin, June 2016, at
https://www.coloradoriverresearchgroup.org/uploads/4/2/3/6/42362959/crrg_tribal_water_rights.pdf.
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Reclamation, working with a group of 10 tribes with significant reserved water rights claims on the
Colorado River, initiated a study known as the 10 Tribes Study.61 The study, published in 2018, estimated
that, cumulatively, the 10 tribes in the study could have reserved water rights (including unresolved
claims) to divert nearly 2.8 MAF per year.62 Of these water rights, approximately 2 MAF per year were
confirmed by a court decree or final settlement and an additional 785,273 AF (mostly in the Upper Basin)
remained unresolved.63 The report estimated that, overall, the 10 tribes are diverting (i.e., making use of)
almost 1.5 MAF of their 2.8 MAF in resolved and unresolved claims. Table 1 shows these figures at the
basin and sub-basin levels.64 According to the study, the majority of unresolved claims among the 10
tribes are Upper Basin claims associated with the Ute Tribe in Utah (370,370 AF per year), the Navajo
Nation in Utah (314,926 AF), and the Navajo Nation in the Upper Basin in Arizona (77,049 AF).
Table 1. Ten Tribes Study: Tribal Water Rights and Diversions
(values in terms of acre-feet per year)
Current Use

Reserved/Settled
Unresolved Water
Total Estimated

Diversions
Water Rights
Rights
Tribal Water Rights
Upper Basin
672,964

1,060,781
762,345
1,823,125
Lower Basin
800,392

952,190
22,928
975,119
Total Basin
1,473,356

2,012,971
785,273
2,798,244
Source: U.S. Bureau of Reclamation, Colorado River Ten Tribes Partnership, Colorado River Basin Ten Tribes Partnership
Tribal Water Study, Study Report, December 2018.
Note: Unresolved water rights include claims for potential water rights that have yet to be resolved.
Drought and the Supply/Demand Imbalance
When the Colorado River Compact was originally approved in 1922, it was assumed based on the
historical record that average annual flows on the river were 16.4 MAF per year.65 According to
Reclamation data, from 1906 to 2020, observed historical natural flows on the river at Lee Ferry, AZ—the historical natural flows on the river at Lee Ferry, AZ—the
common point of measurement for observed basin flows—averaged 14.common point of measurement for observed basin flows—averaged 14.76 MAF annually MAF annually.66 (Figure 3).87 Natural flows Natural flows
from 2000 to from 2000 to 20202022 (i.e., during the ongoing drought) averaged (i.e., during the ongoing drought) averaged considerably less than less than that—12.512.1 MAF annually,88 with this period noted to be the driest 23-year period on record.89 At the same time, consumptive use and losses (e.g., evaporation) in the basin have regularly exceeded natural flows (in particular during the current drought).90 Consumptive use in the basin generally increased from 1971 to 2002 but declined after the 2003 approval of the Quantitative Settlement Agreement (QSA), which in part led to a decrease of consumptive use in the Lower Basin (see below section, “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 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 Arizona v. California decree,92 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 143. 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
annually.67 At the same time, consumptive use and losses in the basin have grown since the compact was
approved and have regularly exceeded natural flows (in particular during the current drought).68

61 The tribes are the Chemehuevi Indian Tribe, Cocopah Indian Tribe, Colorado River Indian Tribes, Fort Mojave Indian Tribe,
Jicarilla Apache Nation, Navajo Nation, Quechan Indian Tribe, Southern Ute Indian Tribe, Ute Indian Tribe, and Ute Mountain
Ute Tribe.
62 U.S. Bureau of Reclamation, Colorado River Ten Tribes Partnership, Colorado River Basin Ten Tribes Partnership Tribal
Water Study, Study Report, December 2018, p. 5.11-1, at https://www.usbr.gov/lc/region/programs/crbstudy/tws/finalreport.html.
Hereinafter, Ten Tribes Study, 2018.
63 Ten Tribes Study, 2018, pp. 5.11-1-5.11-2.
64 Ten Tribes Study, 2018, p. 5.11-4.
65 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.
66 Data available from Bureau of Reclamation, Lower Colorado River Operations, “General Modeling Information,” at
https://www.usbr.gov/lc/region/g4000/riverops/model-info.html. Hereinafter, Bureau of Reclamation Flow Data.
67 Bureau of Reclamation Flow Data, 1906-2020.
68 Consumptive uses and losses include reservoir evaporation and other consumptive use losses, which average in excess of 2
MAF per year.
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Management of the Colorado River: Water Allocations, Drought, and the Federal Role

Consumptive use in the basin generally increased from 1971 to 2002 but declined after the 2003 approval
of the Quantitative Settlement Agreement (QSA) led to a decrease of consumptive use in the Lower Basin
(see below section, “Recent Developments and Agreements”).69 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).
Figure 4. Colorado River Flows, Combined Storage at Lakes Mead and Powell, 1999-2022

Source: Congressional Research Service, based on Bureau of Reclamation natural flow data (https://www.usbr.gov/lc/
region/g4000/NaturalFlow/provisional.html) and Annual Operating Plans for Colorado River reservoirs
(https://www.usbr.gov/uc/water/rsvrs/ops/aop/).
Note: Total storage = 52.3 mil ion acre-feet. *2022 storage reflects conditions as of January 2022.
Observers have noted that Colorado River flows are unlikely to return to 20th century averages and that
future water supply risk is high.70 The period from 2000 to 2021 has been the driest 22-year period on
record, and the current drought in the basin has resulted in 8 of the 20 driest years on record (1906-2020)
having occurred since 2000.71 Overall, natural flows have declined by approximately 20% over the last

69 Consumptive use in the Lower Basin (excluding tributaries) was in excess of 8.41 MAF in 2002 but had decreased to 6. MAF in 2002 but had decreased to 6.79
MAF as of 2020. For more information on consumptive use, see Bureau of Reclamation Consumptive Uses and Losses Reports
for 2006-2010, 2011-2015, and 2016-2020. Analysis of 2009-2020 Lower Basin consumptive use data by CRS, based on Bureau
of Reclamation Colorado River Water Accounting and Use Reports for 2009-2020. Hereinafter, references to consumptive use
data analysis based on these reports are referred to collectively as “CRS Analysis of Colorado River Consumptive Use Data.”
70 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.
71 CRS Analysis of Bureau of Reclamation Flow Data.
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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 17 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 18 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 and that future water supply risk is high.95 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 resulting from climate change.96 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 from rising temperatures.97 As a result, most research has projected continuing reduction in runoff through the mid-21st century.98 Recent Developments and Agreements 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 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 EvaporationManagement of the Colorado River: Water Allocations, Drought, and the Federal Role

century, and some studies attribute more than half of this decline to increasing temperatures resulting
from climate change.72 Further complicating the water-supply picture is that potential precipitation
increases in the region due to climate change are not expected to counteract drying resulting from rising
temperatures.73 As a result, most research projects an ongoing reduction in flows.
A 2012 study by Reclamation highlighted projected long-term imbalances in supply and demand in the
Colorado River Basin.74 In the study, Reclamation noted that the basin had thus far avoided serious
impacts on water supplies due to the significant storage within the system, coupled with the fact that some
Upper Basin states have yet to fully develop the use of their allocations.75 However, Reclamation
projected that in the coming half century, flows would continue to decrease, while drought would increase
in frequency and duration.76 At the same time, Reclamation projected that demand for basin water
supplies would increase, with annual consumptive use projected to rise from 15 MAF in 2012 to 18.1-
20.4 MAF by 2050, depending on population growth.77 Most of the increase in demand was expected to
come from municipal and industrial users.78
Reclamation’s 2012 study posited several potential ways to alleviate future shortages in the basin, such as
alternative water supplies, demand management, drought action plans, water banking, and water
transfers/markets. Some of these options already are being pursued. In particular, some states have
become increasingly active in banking unused Colorado River surface water supplies, including through
groundwater banks or storage of unused surface waters in Lake Mead.
Recent Developments and Agreements
Drought conditions throughout the basin have raised concerns about potential negative impacts on water
supplies. Concerns center on uncertainty that might result if the Secretary of the Interior were to
determine that a shortage condition exists in the Lower Basin, and that related curtailments were
warranted. Some in Upper Basin States are also concerned about the potential for a compact call of Lower
Basin states on Upper Basin states.79 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 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 below.

72 Milley, P.S.D. and K.A. Dunne, “Colorado River flow dwindles as warming-driven loss,” ,” Science, vol. 367, no. 6483 (March , vol. 367, no. 6483 (March
13, 2020), pp. 1252-1255. Hereinafter, 13, 2020), pp. 1252-1255. Hereinafter, Milley, 2020. Also see M. Xiao, B. Udall, D.Milly and Dunne, “Colorado River Flow Dwindles.” Also see Mu Xiao, Bradley Udall, and Dennis P. Lettenmaier, “On the Causes of Declining P. Lettenmaier, “On the Causes of Declining
Colorado 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. Congressional Research Service 19 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 in Upper Basin States are also concerned about the potential for a compact call of Lower Basin states on Upper Basin states. ThisRiver Streamflows,” Water Resources Research 54 (2018), pp. 6739–6756.
73 Milley, 2020.
74 Reclamation 2012 Supply/Demand Study.
75 This is largely due to a lack of development in Wyoming (which uses approximately 500,000 acre-feet of its 1 MAF in
Colorado River supplies) and Utah (which uses approximately 800,000 acre-feet of its 1.7 MAF in supplies).
76 Reclamation 2012 Supply/Demand Study, p. 7.
77 Reclamation 2012 Supply/Demand Study, p. 8. Population growth in central Arizona and on the Front Range of Colorado is
expected to comprise the majority of basin population increases.
78 Reclamation 2012 Supply/Demand Study, Technical Report C, p. C-22. The majority of this demand increase was assumed to
come from Central Arizona and the Front Range in Colorado.
79 A compact call is the commonly used term for the Lower Basin states’ hypothetical attempt to force deliveries of Colorado is the commonly used term for the Lower Basin states’ hypothetical attempt to force deliveries of Colorado
River water under the compact. 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.
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River water under the compact.99 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 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 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 use to an agreement between several California water districts and DOI, California agreed to reduce its use to
the required 4.4 MAF under the Law of the River.the required 4.4 MAF under the Law of the River.80100 It sought to accomplish this aim by quantifying It sought to accomplish this aim by quantifying
Colorado River entitlement levels of several water contractors; authorizing efforts to conserve additional 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-scale, long-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 term agriculture-to-urban water transfers. The QSA also committed the state to a path for toward restoration and restoration and
mitigation related to the Salton Seamitigation related to the Salton Sea, a water body in Southern California that was historically sustained by
Colorado River irrigation runoff from the Imperial and Coachella Valleys.81 in Southern California.101
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 2004.82102 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.83103
2004 Arizona Water Settlements Act
The 2004 Arizona Water Settlements Act (The 2004 Arizona Water Settlements Act (P.L. 108-451, AWSAAWSA,) altered the allocation of CAP water in ) altered the allocation of CAP water in
Arizona.Arizona.84 It ratified three water rights settlements (one in each title) between the federal government and It 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, the State of Arizona, the Gila River Indian Community (GRIC), and the Tohono O’odham Nation,
respectively.respectively.85104 For the state and its CAP water users, the settlement resolved a final repayment cost for For 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.CAP by reducing the water users’ reimbursable repayment obligation from about $2.3 billion to $1.65
7 billion. Additionally, 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 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. 101 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 surrounding areas. For more information on the Salton Sea, see CRS Report R46625, Salton Sea Restoration. 102billion. Additionally, Arizona agreed to new tribal and non-tribal allocations of CAP water so that
approximately half of CAP’s annual allotment would be available to Indian 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.

80 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.
81 For more information on the Salton Sea, see CRS Report R46625, Salton Sea Restoration .
82 Bureau of Reclamation, Record of Decision for the Colorado River Water Delivery Agreement, October 10, 2003, pp 16-19.
Hereinafter, Reclamation, Colorado River Water Delivery Agreement.
83 Reclamation, Colorado River Water Delivery Agreement.
84 P.L. 108-451.
85 Reclamation, Record of Decision for the Colorado River Water Delivery Agreement, October 10, 2003, pp 16-19. 103 Ibid. 104 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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Arizona agreed to new tribal and non-tribal allocations of CAP water so that approximately half of CAP’s 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 Colorado River Interim Guidelines for Another development in the basin was 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 Lower Basin Shortages and the Coordinated Operations for Lake Powell and Lake Mead (2007 Interim
Guidelines). 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 of the agreement began in 2005, when, in response to drought in the Southwest Development of the agreement began in 2005, when, in response to drought in the Southwest
and the decline in basin and the decline in basin water storagewater storage (and a record low point in Lake Powell of 33% active capacity), the , the
Secretary of the Interior instructed Reclamation to develop coordinated strategies for Colorado River Secretary of the Interior instructed Reclamation to develop coordinated strategies for Colorado River
reservoir operations during drought or shortages.reservoir operations during drought or shortages.86106 The resulting guidelines included criteria for releases The resulting guidelines included criteria for releases
from Lakes Mead and Powell determined by “trigger levels” in both reservoirs, as well as a schedule of from Lakes Mead and Powell determined by “trigger levels” in both reservoirs, as well as a schedule of
Lower Basin curtailments at different operational tiers Lower Basin curtailments at different operational tiers (Table 21). Under the guidelines, Arizona and . Under the guidelines, Arizona and
Nevada, which have junior rights to California, would face reduced allocations if Lake Mead elevations Nevada, which have junior rights to California, would face reduced allocations if Lake Mead elevations
dropped below 1,075 feet. At the time, it was thought that the 2007 Guidelines would significantly reduce 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 1,025 feet. the risk of Lake Mead falling to 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.storage that was classified as ICS was 2.8499 MAF.107 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. MAF (Figure 5).87
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, end of 2026). Thus, beginning in 2020, Reclamation coordinatedReclamation began coordinating a review on the effectiveness of the 2007 a review on the effectiveness of the 2007
guidelines. Reconsultation on the 2007 guidelines also is guidelines in 2020, and in 2022 formally initiated the review process for post-2026 operations.108 The review is expected to encompass negotiations related to expected to encompass negotiations related to
renewal of the Upper and Lower Basin DCPs, which are an overlay on the 2007 guidelines (see below renewal of the Upper and Lower Basin DCPs, which are an overlay on the 2007 guidelines (see below
section, section, “2019 Drought Contingency Plans”). ).

86105 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 Prior to this time, the Secretary of the Interior had the authority to declare a shortage, but no shortage criteria had been publicly 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.) announced or published. (Criteria for surplus operations were put in place in 2001.)
87107 Bureau of Reclamation, Bureau of Reclamation, Colorado River Accounting and Water Use Report, Calendar Year 20202021, at https://www.usbr.gov/lc/, at https://www.usbr.gov/lc/
region/g4000/wtracct.html. region/g4000/wtracct.html.
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Figure 5. U.S. Lower Basin States: Intentionally Created Surplus Balance, 2010-2020

Source: Figure by CRS, based on data from Bureau of Reclamation, Colorado River Accounting and Water Use Report,
Calendar Years 2010-2020, at https://www.usbr.gov/lc/region/g4000/wtracct.html.
Pilot 108 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,” 87 Federal Register 37884-37888, June 24, 2022. Congressional Research Service 21 link to page 26 Management of the Colorado River: Water Allocations, Drought, and the Federal Role 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
California, and Denver Water) executed a memorandum of understanding to provide funding for California, and Denver Water) executed a memorandum of understanding to provide funding for
voluntary conservation projects and reductions of water use. voluntary conservation projects and reductions of water use. TheseThe activities activities outlined in the memorandum had the goal of developing had the goal of developing
new new system water,,88109 to be applied toward storage in Lake Mead, by the end of 2019. to be applied toward storage in Lake Mead, by the end of 2019.89110 Congress formally Congress formally
authorized federal participation in these efforts in the Energy and Water Development and Related
Agencies Appropriations Act, 2015 (P.L. 113-235, Division D), with an initial sunset date for the authority

88 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.
89 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.
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at the end of FY2018.90authorized federal participation in these efforts, known as the Pilot System Conservation Program, in the Energy and Water Development and Related Agencies Appropriations Act, 2015 (, Division D). The Energy and Water Development and Related Agencies Appropriations Act, The Energy and Water Development and Related Agencies Appropriations Act,
2019 2019 ((P.L. 115-244, Division A) extended the authority through the end of FY2022, with the stipulation , 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 that Upper Basin agreements could not proceed without the participation of the Upper Basin states
through the Upper Colorado River Commission.through the Upper Colorado River Commission.91 As of September 2019, Reclamation estimated that the
Lower Basin program had resulted in a total of 175,347 AF of system water conserved The authority was most recently extended through FY2024 in Division CC of the Consolidated Appropriations Act, FY2023 (). 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 , at an average cost
of $170 per AF.of $170 per AF.92111 Additional projects also were carried out in the Upper Basin by the Upper Colorado Additional projects also were carried out in the Upper Basin by the Upper Colorado
River Basin Commission; these efforts ended in 2018.River Basin Commission; these efforts ended in 2018.93112
Minute 319 and Minute 323 Agreements with Mexico94Mexico113
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 2012.95114 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 extendedsupport the ecological health of the Colorado River Delta. It also extended the initial Mexican cutback 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 additional cutbacks that would be triggered if DCPs are approved by U.S. basin states (see the following 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
both the Upper Basin and the Lower Basin. These plans required final authorization by Congress to be
implemented. On April 16, 2019, Congress authorized the DCP agreements in the Colorado River
Drought Contingency Plan Authorization Act (P.L. 116-14). The DCPs are an overlay of the 2007 Interim
Guidelines discussed above, thus similar to the 2007 guidelines; they are scheduled to be in place through
2026. 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.96

90 P.L. 113-235, §206.
91 P.L. 115-244, §205.
92 109 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 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 August 2, 2022.
93January 17, 2023. 112 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/.
94113 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.
95 The text of these minutes is available from the International Boundary and Water Commission at 114 International Boundary & Water Commission, “Minutes between the United States and Mexican Sections of the IBWC,” at https://www.ibwc.gov/https://www.ibwc.gov/
Treaties_Minutes/Minutes.html.
96 While such a mechanism exists for the Lower Basin, a comparable program has not been developed in the Upper Basin.
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Treaties_Minutes/Minutes.html. Congressional Research Service 22 link to page 28 Management of the Colorado River: Water Allocations, Drought, and the Federal Role 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 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 Act (); like the 2007 guidelines, these plans are scheduled to be in place through 2026. At the time of their Commented [KJ1]: Missing a year? 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 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., “minimum power pool” (i.e., 3,490 feet, the minimum elevation needed to run the dam’s hydroelectric plant). Under 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 Canyon Dam 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 Reservoir, 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, potentially 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 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 Program, has yet to benot been formally established. It would entail willing seller/buyer agreements allowing for 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 resulted in additional water conserved in Lake Powell. A future Upper Basin DCP Demand Management Program may Demand Management Program may
expand on some of those efforts. 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 2022.97117 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 released
a draft plan in early 2022.98 These efforts are expected to supplement Lake Powell storage, although the
exact magnitude is uncertain and there remains a possibility of the lake level dropping to minimum power
pool by 2024 (Figure 6).

97, and approved this plan in 2022.118 Reclamation modeling indicates that these efforts, combined with improved hydrology in 2023, are expected to stabilize Lake Powell storage levels in the next two years (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 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).
98118 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 65. Lake Powell End of -of-Month Elevation Projections
( (August 2022January and March 2023 24-month study inflow scenarios) 24-month study inflow scenarios)

Source: U.S. Bureau of Reclamation, “24-Month Study Projections,” U.S. Bureau of Reclamation, “24-Month Study Projections,” August 2022March 2023, at https://www.usbr.gov/lc/region/, at https://www.usbr.gov/lc/region/
g4000/riverops/24ms-projections.html. g4000/riverops/24ms-projections.html.
Notes: WY= WY = Water Year. DROAWater Year. DROA = Drought Response Operations Agreement. = 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
1,1,045 feet. At the same time, the025 feet. The Lower Basin DCP includes—for the first time—delivery cutbacks for 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 California. These curtailments begin with a 200,000 AF delivery reduction at Lake Mead elevations of
1,040-between 1,040 and 1,045 feet and would increase by 50,000 AF for each additional 5 foot drop in Lake Mead 1,045 feet and would increase by 50,000 AF for each additional 5 foot drop in Lake Mead
elevationelevation below 1,040 feet, to as much as 350,000 AF at elevations of 1,025 feet or lower. , to as much as 350,000 AF at elevations of 1,025 feet or lower.
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 21.
In addition to the state-level reductions, under the Lower Basin DCPIn addition to the state-level reductions, under the Lower Basin DCP, Reclamation also agreed to pursue Reclamation also agreed to pursue
efforts to add 100,000 AF or more of efforts to add 100,000 AF or more of “system watersystem water” within the basin. Some of the largest and most 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 previous changes under the 2004 AWSA, a large group of agricultural users facewere already facing major cutbacks to their major cutbacks to their
CAP water supplies. The Tier Zero Arizona curtailment of 192,000 AF at Tier Zero represents a 12%
reduction in CAP water supplies.
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Table 21. 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
2007 InterimShortage
Delivery
Scarcity
Total Volume of Curtailment
Shortage Guidelines
Reductions
DCP Curtailment
Conting. Plan
(% of Lower Colorado River Apportionment)
Lake Mead
Elevation
Lower
Lower Elevation (ft)
AZ
NV
Mexico
AZ
NV
CA
Mexico
AZ
NV
CA
Basin
Mexico
1,090 - 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 1,075
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 1,050
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 1,045
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 1,040
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 1,035
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 1,030
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 <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.

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

AtIn 2019, at the time of the time of its passage, Reclamation notedthe passage of the Colorado River Drought Contingency Plan Authorization Act, Reclamation asserted that the Lower Basin DCP that the Lower Basin DCP decreased the chance of
would significantly reduce the risk of Lake Mead elevations falling below Lake Mead elevations falling below 1,020 feet, which would be a critically low level.99critical elevation of 1,020 feet.119 Combined Combined
with the commitments from Mexico, total planned cutbacks under shortage scenarios (i.e., all with 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.100120 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 finalizedDCP was finalized, and is projected to continue to and is projected to continue to decline (Figure 7). This hasdecline despite improved hydrology in 2023 (Figure 6). These developments have triggered triggered
additional Lower Basin conservation efforts. additional Lower Basin conservation efforts.
Figure 76. Lake Mead End of Month Elevation Projections
( (August 2022January 2023 and March 2023 24-month study inflow scenarios) 24-month study inflow scenarios)

Source: Source: U.S. Bureau of Reclamation, “24-Month Study Projections,” U.S. Bureau of Reclamation, “24-Month Study Projections,” August 2022March 2023, at , at
https://www.usbr.gov/lc/https://www.usbr.gov/lc/region/g4000/riverops/24ms-projections.html. 2023 Draft Supplemental Environmental Impact Statement At a June 14, 2022, Senate hearing, the Commissioner of Reclamation announced that basin states would need to conserve between 2 MAF and 4 MAF in 2023 and 2024 to protect Lake Mead and Lake Powell storage volumes over the near-term (2023-2026) period.121 These amounts would be in addition to the previous commitments discussed above. At the time, the 119 2019 House Natural Resources DCP Hearing. 120 For a summary of the curtailments that add up to this amount, see “1,090 - >1,075” row of Table 1. 121 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. 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. Congressional Research Service 26 Management of the Colorado River: Water Allocations, Drought, and the Federal Role 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 No major water savings commitments were announced in response to Reclamation’s June statement.123 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 are proceeding separately) so as to address continued low runoff conditions in the basin. As part of the proposed guideline modifications, Reclamation published its notice of intent to prepare a supplemental environmental impact statement (SEIS) in the Federal Register in November 2022.124 In the SEIS, 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, 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 submitted a combined proposal for Reclamation modeling (the Six State Proposal) in response to the November SEIS notice.126 California submitted its own proposal (the California Proposal) separately. 127 The Six State Proposal requested that Reclamation model in its SEIS 1.543-1.943 MAF per year in new delivery reductions on Lower Colorado River Basin contractors (i.e., reductions in addition to previous commitments). Those additional reductions would be implemented through two 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 Mexico, which 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 use levels.128 Second, additional operational tier changes and delivery reductions are tied to Lake Mead elevations of 1,050 feet and lower.129 The Six State Proposal’s cumulative reductions from current levels would be proportionally greater for California than for Arizona and Nevada.130 For its part, the California Proposal would include 1.0-1.95 MAF per year in new delivery reductions for Lower Basin contractors (not varying based on evaporation), depending on Lake Mead 122 2022 Drought Hearing. 123region/g4000/riverops/24ms-projections.html.
500+ Plan
The Lower Basin DCP included a provision that if Reclamation’s modeling (which includes all of
the aforementioned conservation efforts) indicates a possibility of Lake Mead reaching an
elevation at or below 1,030 feet, the Secretary of the Interior and the Lower Basin states would
consult on additional measures to avoid and protect Lake Mead declining below 1,020 feet.101
This provision was triggered in Reclamation’s August 2021 24-month study, which projected the

99 2018 Reclamation DCP Presentation. Currently, there are no agreed-upon curtailment levels governing operations
below 1,020 feet; thus, that level represents an unknown and likely more severe level of curtailment affecting more
users than those affected under the 2007 guidelines.
100 For a summary of the curtailments that add up to this amount, see “1,090 - >1,075” row of Table 2.
101 Reclamation, Agreement Concerning Colorado River Drought Contingency Management and Operations, May 19,
2020, at https://www.usbr.gov/dcp/docs/final/Companion-Agreement-Final.pdf.
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possibility for such a scenario by 2023 under its “Probable Minimum Inflow” scenario.102 In
response, Lower Basin parties and the DOI met and in December 2021 agreed on a new set of
actions in a memorandum of understanding, known as the 500+ Plan. This plan calls for
contributions of up to $100 million by Lower Basin users ($40 million from the Arizona
Department of Water Resources and $20 million each from the Central Arizona Water
Conservation District, the Metropolitan Water District of Southern California, and the Southern
Nevada Water Authority), plus another $100 million from the federal government, which
collectively will result in the conservation of an additional 500,000 AF in Lake Mead in each of
2022 and 2023 (i.e., 1 MAF).103 Federal funding for these conservation efforts was made
available through a combination of discretionary appropriations to Reclamation, as well as
supplemental funding in the Infrastructure Improvement and Jobs Act (P.L. 117-58).
Potential for Additional Curtailments
At a June 14, 2022, congressional hearing, the Commissioner of Reclamation announced that
basin states would need to conserve between 2 MAF and 4 MAF in 2023 to protect Lake Mead
and Lake Powell storage volumes over the near-term period (2023-2026).104 These amounts
would be in addition to the previous commitments discussed above. The estimate was the result
of a 2022 Protection Volume Analysis by Reclamation.105 The Commissioner noted that if these
targets are not met with voluntary actions by August 2022, DOI was prepared to act
unilaterally.106 In a July 18, 2022, letter to Reclamation, the Upper Colorado River Commission In a July 18, 2022, letter to Reclamation, the Upper Colorado River Commission
declined to contribute a specific volume of cutbacks to these efforts, declined to contribute a specific volume of cutbacks to these efforts, and instead instead layinglaid out a five- out a five-
point plan as the basis for its water conservation efforts.107 As of early September 2022, no new
curtailments or agreements had been announced.
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
and oversight of facility operations, construction, and programs to protect and restore endangered
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

102 Bureau of Reclamation, Operation Plan for Colorado River System Reservoirs, August 2021 24-Month Study,
Minimum Probable Inflow, at https://www.usbr.gov/lc/region/g4000/24mo/2021/AUG21_MIN.pdf. 24-Month Study
Reports are available at Bureau of Reclamation, Operation Plan for Colorado River System Reservoirs (24-Month
Study), at https://www.usbr.gov/lc/region/g4000/24mo/index.html.
103 Similar to the aforementioned efforts under the System Conservation Program, funding for increased efficiency and
decreased deliveries (e.g., through fallowing programs) are expected to be among the efforts funded through the 500+
Plan.
104 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.
Hereinafter “2022 Drought Hearing.”
105 See, Bureau of Reclamation, Colorado River System Mid Term Projections, June 16, 2022, at https://www.usbr.gov/
ColoradoRiverBasin/documents/20220616-ColoradoRiverSystemMid-termProjections-Presentation.pdf.
106 2022 Drought Hearing.
107 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-
Letter-to-Reclamation.pdf.
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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. Bureau of Reclamation, July 18, 2022, at http://www.ucrcommission.com/wp-content/uploads/2022/07/2022-July-18-Letter-to-Reclamation.pdf. 124 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 Coordinated Operations For Lake Powell and Lake Mead,” 87 Federal Register 69042, November 17, 2022. Hereinafter, November 2022 Notice. 125 November 2022 Notice. 126 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. Hereinafter, Six State Proposal. 127 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. 128 This amount also assumes the assessment of evaporative losses on Mexico. 129 Six State Proposal. These reductions would move the current Tier 3 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 of 1,030 feet or lower. 130 CRS analysis of Six State Proposal. Congressional Research Service 27 link to page 34 link to page 34 Management of the Colorado River: Water Allocations, Drought, and the Federal Role 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 beginning at 1,025 feet. For the first 1.0 MAF, the California Proposal’s reductions would be proportionally greater for Arizona and Nevada than for itself; the state also did not assume any reductions for Mexico.131 Both state proposals also suggest 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. On April 11, 2023, Reclamation released its draft SEIS.132 The document included modeling for a “no action” alternative and two action alternatives. The primary difference between the two action alternatives is the approach for apportioning reductions for new shortage operations at Lake Mead. Action Alternative 1 assumes additional reductions based on priority order of water rights.133 Action Alternative 2 assumes the Secretary would use existing federal authorities to 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 in almost all reductions being borne by Arizona and Nevada under Alternative 1, whereas Alternative 2 would apportion reductions among Lower Basin users in all states 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. 131 The proposal did not specify the allocation of reductions in excess of 1.0 MAF. 132 Bureau of Reclamation, Near Term Colorado River Operations, Draft Supplemental Environmental Impact Statement, April 2023, at https://www.usbr.gov/ColoradoRiverBasin/SEIS.html. Hereinafter, 2023 Draft SEIS. 133 As explained in the draft SEIS, “[p]riority refers 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 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. 134 The draft SEIS did not include reductions based on evaporation similar to the Six State State Proposal, although the 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 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. 135 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 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 an alternate basis for apportioning shortages, subject to statutory constraints. Ibid., pp. 592–593. Congressional Research Service 28 Management of the Colorado River: Water Allocations, Drought, and the Federal Role 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 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. Congressional Research Service 29 Management of the Colorado River: Water Allocations, Drought, and the Federal Role 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. 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 Congressional Research Service 30 link to page 36 link to page 37 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 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. Reclamation’s draft SEIS analysis projects that both action alternatives would significantly reduce the chances of Lake Powell reaching minimum power pool in 2024-2026 (Figure 8). For Lake Mead, Reclamation projects that the alternatives would initially reduce reservoir storage in 2023 and 2024 (due to reduced releases from Lake Powell), before increasing these storage levels in 2025 and 2026 (Figure 9). Reclamation also projects that the action alternatives would keep Lake Mead above its minimum power pool level (950 ft) under most scenarios. The SEIS analyzes a variety of other projected impacts associated with each alternative, as well as additional analysis of the likely cuts for individual contractor groups within each state.137 136 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 See 2023 Draft SEIS, pp 2-24–2-38. Congressional Research Service 31 Management of the Colorado River: Water Allocations, Drought, and the Federal Role Figure 8. Lake Powell Projected Pool Elevations for 2023 SEIS Alternatives Source: Bureau of Reclamation, Near Term Colorado River Operations, Draft Supplemental Environmental Impact Statement, April 2023. Congressional Research Service 32 Management of the Colorado River: Water Allocations, Drought, and the Federal Role Figure 9. Lake Mead Projected Pool Elevations for 2023 SEIS Alternatives Source: Bureau of Reclamation, Near Term Colorado River Operations, Draft Supplemental Environmental Impact Statement, April 2023. When Reclamation released the draft SEIS, departmental officials framed the SEIS alternatives as “bookends” meant to define the problem and motivate state officials to collaborate on a compromise option in the final SEIS.138 For example, the department stated that it does not plan to adopt an approach based entirely on the Law of the River; to date no state (including California) has advocated for such an approach.139 The draft SEIS must undergo a 45-day public comment period, and a final SEIS is expected to be released in summer 2023. 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 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 138 Jennifer Yachnin, “Interior Offers Extremes on Colorado River Cuts to Spur Compromise,” E&E News, April 11, 2023. 139 Ibid. Congressional Research Service 33 Management of the Colorado River: Water Allocations, Drought, and the Federal Role 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 account for a portion of overall project budgets. For example, in FY2020, approximately 3640% of % of
theLower Colorado River Region’s overall budget was funded with discretionary appropriations, with the remainder of funding budget was funded with discretionary appropriations, with the remainder of funding came
coming from power revenues (which are made available without further appropriation) and nonfederal from power revenues (which are made available without further appropriation) and nonfederal
partners.partners.108140 In recent years, Congress has also authorized and appropriated funding that has In recent years, Congress has also authorized and appropriated funding that has
targeted the Colorado River Basin in general (e.g., the Pilot System Conservation Plan). Congress targeted the Colorado River Basin in general (e.g., the Pilot System Conservation Plan). Congress
may choose to extend or amend may choose to extend or amend these and other authorities specific to the authorities specific to the basinbasin or alter basin funding levels. .
While discretionary appropriations for the Colorado River are of ongoing interest to Congress, While discretionary appropriations for the Colorado River are of ongoing interest to Congress,
Congress Congress also may addresshas also addressed Colorado River funding outside of the regular appropriations process. Colorado River funding outside of the regular appropriations process.
In the 117th Congress, in Section 50233 of In the 117th Congress, in Section 50233 of P.L. 117-169 (popularly known as the Inflation (popularly known as the Inflation
Reduction Reduction ActAct, IRA), Congress provided $4.0 billion for projects that mitigate drought in the 17 arid ), Congress provided $4.0 billion for projects that mitigate drought in the 17 arid
and semiarid and semiarid reclamation states in the West, in the West,141 with priority given to Colorado River Basin with priority given to Colorado River Basin
activities. These activities include compensation for reduction in water diversions and funding for
system conservation and ecosystem restoration to address drought in a river basin or inland water
body.
Tribal Water Rights Settlements and Leasing
Most tribal water rights are senior to other users and thus are likely to play an 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, will have ramifications for water availability
in the basin. 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; a portion of
this water has been developed to date. Congress may be asked to consider new settlements that
would add to this total. For instance, both S. 4104 and H.R. 7633 would authorize a water rights
settlement with the Hualapai Tribe in Arizona, including approval of that tribe’s water rights and
funding for infrastructure to access this water. Congress is also considering new authority for
some tribes to market their water rights to other basin water users. In the 117th Congress, S. 3308
would authorize the Colorado River Indian Tribes (CRIT) to enter into agreements to lease a
portion of their Colorado River water rights. Currently, some tribes have the ability to lease their
water, whereas others (such as CRIT) do not.
Plans for New and Augmented Water Storage, Conveyance
Some states in the Upper Basin have indicated their intent to further develop their Colorado River
water entitlements. In the 115th Congress, Section 4310 of America’s Water Infrastructure Act
(P.L. 115-270) authorized the Secretary of the Interior to enter into an agreement with the State of
Wyoming whereby the state would fund a project to add erosion control to Fontenelle Reservoir
in the Upper Basin. The project would allow the state to potentially utilize an additional 80,000
acre-feet of water storage on the Green River, a tributary of the Colorado River.

108 Bureau of Reclamation, Lower Colorado Region Annual Report, FY2018, at https://www.usbr.gov/lc/docs/
LCRegionReportFY18.pdf.
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Another project that would develop Upper Basin waters is the activities. This funding is available through FY2026 and may be used for a variety of activities, including some of the previously authorized activities discussed above, as well as compensation for new efforts. Reclamation announced initial plans for this funding on October 12, 2022, in the form of a new program, the Lower Colorado River Basin System Conservation and Efficiency Program.142 The program has three components:  Under the first component (1a), Colorado River water delivery contractors or 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 acre-foot for a two-year agreement, and $400 per acre-foot for a three-year agreement. These proposals were due in November 2022.  For the second component (1b), Reclamation accepted proposals for additional water conservation and efficiency projects that could involve a variety of pricing options as proposed by Colorado River water delivery contractors or entitlement holders. These proposals were due in November 2022.  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 system conservation. These proposals were expected to be solicited in early 2023. While some agreements under this program have been announced,143 the full magnitude of water savings that might result from these voluntary agreements is unclear. If the agreements are 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. 142 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 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 agreement with the Coachella Valley Water District to conserve 30,000 AF of water per year (for three years) with $12 Congressional Research Service 34 Management of the Colorado River: Water Allocations, Drought, and the Federal Role 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 water consumption levels. 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 restoration activities over the 2022-2026 timeframe.144 Restoration of the Sea is a high priority of the Imperial Irrigation District, one of the largest water rights holders on the Colorado River.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 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 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 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 Indian Tribes Water Resiliency Act of 2022,).146 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 proposed Lake Powell Pipeline
(LPP), (LPP), which would direct approximately 86,000 would direct approximately 86,000 acre-feetAF of Utah’s Upper Basin Colorado River of Utah’s Upper Basin Colorado River
BasinBasin annual apportionment from Lake Powell to Washington County, UT (i.e., the St. George, UT, area, 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).which is technically located within the Lower Basin drainage area).109147 The pipeline would begin The pipeline would begin
near Glen Canyon Dam in Arizona and would run through Arizona and Utah to Sand Hollow near Glen Canyon Dam in Arizona and would run through Arizona and Utah to Sand Hollow
Reservoir near St. George, UT. Reclamation Reservoir near St. George, UT. Reclamation has been designatedis the lead agency for the project the lead agency for the project
under NEPA and is coordinating an under NEPA and is coordinating an Environmental Impact Statementenvironmental impact statement (EIS) for the most recently (EIS) for the most recently
proposed version of the project.proposed version of the project.110 Supporters in Utah148 million in IRA funding. See White House, “Fact Sheet: Biden-⁠Harris Administration Announces New Investments to Protect the Colorado River System,” April 6, 2023. 144 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. 145 For more on Salton Sea restoration, see CRS In Focus IF11104, Salton Sea Management and Restoration Efforts, by Pervaze A. Sheikh and Charles V. Stern. 146 Prior to the legislation’s enactment, these tribes, who were awarded their water rights under the Arizona v. California decree, were not able to lease their water. This is not the case for most other tribes with Colorado River water rights. 147 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. 148 For project NEPA documents and studies, see https://www.usbr.gov/uc/DocLibrary/EnvironmentalImpactStatements/LakePowellPipeline/index.html#intro. Congressional Research Service 35 Management of the Colorado River: Water Allocations, Drought, and the Federal Role 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 argue that the pipeline is needed to provide
a second primarya secondary water source for the St. George area water source for the St. George area, (in addition to in addition to its primary water source from the the Virgin RiverVirgin River). However, . Some
environmental groups have argued that the proposed development and diversion of additional 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 Upper Basin waters is ill-advised in light of climate change and the basin’s issues with over-over-
allocation. These groups have argued for major changes to the scope of the EIS.111allocation.149 The six other The six other
Colorado River Basin states have raised concerns related to the proposed LPP’s “legal and Colorado River Basin states have raised concerns related to the proposed LPP’s “legal and
operational issues,” and operational issues,” and they have raised concerns withhave criticized the use of the LPP NEPA process as the LPP NEPA process as thea de facto de facto
forum for resolving a conflict among basin states. The six states previously requested that 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 consensus Reclamation refrain from issuing a final EIS until these issues can be resolved on a consensus
basis.basis.112150 Some groups that oppose new infrastructure development on the Colorado River also have proposed demolition of existing 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 would be a cheaper and less politically problematic option than other options (e.g., fallowing Upper Basin farms to conserve water).151 For their part, water and power users and most 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 the reliability of using river bypass tubes at the dam to enable Lower Basin releases at storage levels below minimum power pool.152 Reclamation is also studying the efficacy of physical 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. 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.154 Congress also may be 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. 149 Letter from Utah Rivers Council et al. to Rick Baxter, Program Manager, Bureau of Reclamation Provo Area Office, September 8, 2020. 150
Drought Contingency Plan Implementation and Future Basin
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.113 Congress also may be
interested in broader basin planning, including new and existing efforts to plan for increased
demand in the basin and stretch limited basin water supplies.
Federally led efforts to extend the 2007 Interim Guidelines (including the DCPs), which expire at
the end of 2026, look to be the next major set of negotiations in the consensus-based management
of the Colorado River. These “reconsultation” efforts, including any major changes to existing
agreements, are seen as key to managing the basin’s future water resources. At the same time,
new agreements that would protect water supplies in the short-term, such as the 500+ Plan, an
Upper Basin Demand Management Program, and DROA Drought Plans, could themselves result
in additional congressional involvement in funding, oversight, and/or enactment of new
authorities. On June 20, 2022, Reclamation published a “pre-scoping” notice in the Federal

109 While St. George, UT, is technically within the Lower Colorado River Basin’s drainage, as previously discussed,
Utah’s state allocation comes out of waters available to the Upper Basin. Thus, the LPP would utilize Upper Basin
waters.
110 For project NEPA documents and studies, see https://www.usbr.gov/uc/DocLibrary/
EnvironmentalImpactStatements/LakePowellPipeline/index.html#intro.
111 Letter from Utah Rivers Council et al. to Rick Baxter, Program Manager, Bureau of Reclamation Provo Area Office,
September 8, 2020.
112 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.
113151 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. 152 Reclamation, “Interior Department Announces Actions to Protect Colorado River System, Sets 2023 Operating Conditions for Lake Powell and Lake Mead,” August 16, 2022. 153 Ibid. 154 For instance, 2021 and 2022 hearings on drought in the western United States included extensive discussion of 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, drought conditions in the Colorado River Basin. See U.S. Congress, House Committee on Natural Resources,
Subcommittee on Water, Oceans, and Wildlife, 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, , 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. , 117th Cong., 2nd sess., June 14, 2022.
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Management of the Colorado River: Water Allocations, Drought, and the Federal Role

Register seeking input on how to foster participation by stakeholders in the National
Environmental Policy Act (NEPA) process to develop post-2026 basin operations.114 A formal
notice for NEPA scoping activities is expected in 2023.

Author Information

Charles V. Stern
Pervaze A. Sheikh
Specialist in Natural Resources Policy
Specialist in Natural Resources Policy


Concluding Observations 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 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 a drought dating to 2000 has exacerbated this issue. Although recent agreements have marginally reduced usage, basin-wide consumptive use (including evaporation) has continued to exceed natural flows in most years. The resulting drawdown of basin storage has left Lakes Mead and Powell at historically low levels that threaten both hydropower production and water deliveries throughout the basin. Water flow projections estimate that flows will continue to decrease, whereas new demands and diversions (e.g., development of tribal water rights) suggest that competition for this water among users will continue to increase. 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 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 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, safety, and other uses, is a central issue currently facing decisionmakers. Other questions, including what changes to infrastructure (e.g., alterations to dam and water delivery infrastructure), accounting (e.g., whether and how to account for evaporation in the Lower Basin), and/or the basis for basin water management (e.g., water allocations based on inflows rather than set amounts) are also likely to figure into future discussions and negotiations. Author Information Charles V. Stern Kristen Hite Specialist in Natural Resources Policy Legislative Attorney Pervaze A. Sheikh Specialist in Natural Resources Policy Congressional Research Service 37 Management of the Colorado River: Water Allocations, Drought, and the Federal Role

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114 Department of the Interior, Bureau of 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,”
87 Federal Register 37884-37888, June 24, 2022.
Congressional Research Service Congressional Research Service
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