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

Changes from October 13, 2020 to December 15, 2020

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

Management of the Colorado River: Water
~~October 13~~December 15, 2020 , 2020
~~Allocation~~Allocations, Drought, and the Federal Role
Charles V. Stern
The Colorado River Basin covers more than 246,000 square miles The Colorado River Basin covers more than 246,000 square miles in seven U.S. states in seven U.S. states
Specialist in Natural Specialist in Natural
(Wyoming, Colorado, Utah, New Mexico, Arizona, Nevada, and California) and (Wyoming, Colorado, Utah, New Mexico, Arizona, Nevada, and California) and
Mexico. Resources Policy Resources Policy
~~Mexico.~~ Pursuant to federal law, the Bureau of Reclamation (part of the Department of Pursuant to federal law, the Bureau of Reclamation (part of the Department of

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

The water apportioned to The water apportioned to ~~users~~states on the Colorado River is widely acknowledged to be in on the Colorado River is widely acknowledged to be in
excess of excess of the river’s natural flows. Although a majority of the basin’s precipitation originates in the Upper Basin, the Lower Basin also has been extensively developed by the federal government. ~~the river’s natural flows.~~ Consumptive uses of Colorado River water Consumptive uses of Colorado River water ~~typical y~~

typically exceed natural flows, causing an imbalance in the basin’s available supplies and demands. These trends are exceed natural flows, causing an imbalance in the basin’s available supplies and demands. These trends are
exacerbated by a drought in the basin dating to 2000, which has raised the prospect of water delivery curtailments exacerbated by a drought in the basin dating to 2000, which has raised the prospect of water delivery curtailments
and decreased hydropower production, among other things. In the future, observers expect that increasing demand and decreased hydropower production, among other things. In the future, observers expect that increasing demand
for water supplies, coupled with the effects of climate change, for water supplies, coupled with the effects of climate change, ~~wil~~ will further strain the basin’s limited water further strain the basin’s limited water
supplies. supplies.
River Management
The The Law of the River is the commonly used shorthand for the multiple laws, court decisions, and other documents is the commonly used shorthand for the multiple laws, court decisions, and other documents
governing Colorado River operations. The foundational document of the Law of the River is the Colorado River governing Colorado River operations. The foundational document of the Law of the River is the Colorado River
~~Compact~~ Compact of 1922. Pursuant to the compact, the basin states established a framework to apportion the water of 1922. Pursuant to the compact, the basin states established a framework to apportion the water
supplies between the Upper and Lower Basins of the Colorado River, with the dividingsupplies between the Upper and Lower Basins of the Colorado River, with the dividing line between the two line between the two
basins at Lee Ferry, basins at Lee Ferry, AZA Z (near the Utah border). The Upper and Lower Basins each were (near the Utah border). The Upper and Lower Basins each were ~~al ocated 7.5 mil ion~~allocated 7.5 million acre- acre-
feet (MAF) feet (MAF) ~~annual y~~ annually under the compact (plus the right to an increase of 1 MAF per year in the Lower Basin)~~under the compact~~; an additional 1.5 MAF in annual flows was made available to Mexico ; an additional 1.5 MAF in annual flows was made available to Mexico
under a 1944 treaty. Future agreements and court decisions addressed other issues (including intrastate under a 1944 treaty. Future agreements and court decisions addressed other issues (including intrastate ~~al ocations~~
allocations of flows), and subsequent federal legislation provided authority and funding for federal facilities that of flows), and subsequent federal legislation provided authority and funding for federal facilities that ~~al owed~~
allowed users to develop their users to develop their ~~al ocations. A~~ allocations. A 1963 Supreme Court ruling also confirmed that Congress designated1963 Supreme Court ruling also confirmed that Congress designated the the
Secretary of the Interior as the Secretary of the Interior as the water master for the Lower Basin, a role in which the federal government manages for the Lower Basin, a role in which the federal government manages
the delivery of the delivery of al all water below Hoover Dam. water below Hoover Dam.
Reclamation and basin stakeholders closely track the status of two large reservoirs—Lake Reclamation and basin stakeholders closely track the status of two large reservoirs—Lake ~~Powel~~ Powell in the Upper in the Upper
Basin and Lake Mead in the Lower Basin—as an indicator of basin storage conditions. Under recent Basin and Lake Mead in the Lower Basin—as an indicator of basin storage conditions. Under recent ~~guidelines,~~
criteria, dam releases from these facilities are tied to specific water storage levels. For Lake Mead, the first operational dam releases from these facilities are tied to specific water storage levels. For Lake Mead, the first operational
shortage tier (“Tier Zero”) under which Arizona’s and Nevada’s shortage tier (“Tier Zero”) under which Arizona’s and Nevada’s ~~al ocations~~allocations are decreased by specified levels are decreased by specified levels
would be triggered if Lake Mead’s January 1 elevation were expected to would be triggered if Lake Mead’s January 1 elevation were expected to ~~fal~~ fall between 1,075 feet and 1,090 feet between 1,075 feet and 1,090 feet
above mean sea level. This operational tier is currently in effect, and this is expected to remain the case in the near above mean sea level. This operational tier is currently in effect, and this is expected to remain the case in the near
future. As of August 2020, Reclamation projected a 49% chance, depending on the hydrology assumed, for future. As of August 2020, Reclamation projected a 49% chance, depending on the hydrology assumed, for
additional curtailments (i.e., a Tier One or greater shortage) at Lake Mead by 2024. additional curtailments (i.e., a Tier One or greater shortage) at Lake Mead by 2024.
Operational Changes and Drought Contingency Plans
Despite earlierDespite earlier efforts to efforts to ~~al eviate~~alleviate future shortages, the basin’s hydrological outlook future shortages, the basin’s hydrological outlook ~~general y~~generally has worsened in has worsened in
recent years. After several years of negotiations, in 2019 Reclamation and the basin states transmitted to Congress recent years. After several years of negotiations, in 2019 Reclamation and the basin states transmitted to Congress
plans to further plans to further ~~al eviate~~ alleviate stress on basin water supplies. Congress authorized these plans, known as the drought stress on basin water supplies. Congress authorized these plans, known as the drought
contingency plans (DCPs) for the Upper and Lower Basinscontingency plans (DCPs) for the Upper and Lower Basins , in April 2019 in the Colorado River Drought , in April 2019 in the Colorado River Drought
Contingency Plan Authorization Act (P.L. 116-14). Among other things, the DCPs obligate Lower Basin states to Contingency Plan Authorization Act (P.L. 116-14). Among other things, the DCPs obligate Lower Basin states to
~~additional~~ additional water delivery water delivery ~~cutbacks~~reductions at specified storage levels (i.e., at specified storage levels (i.e., ~~cutbacks~~reductions beyond previous curtailment plans), beyond previous curtailment plans),
commit Reclamation to additional water conservation efforts, and put in place plans to coordinate Upper Basin commit Reclamation to additional water conservation efforts, and put in place plans to coordinate Upper Basin
~~Congressional Research Service~~

operations to protect Lake operations to protect Lake ~~Powel~~ Powell storage levels and hydropower generation. Despite the success of DCP storage levels and hydropower generation. Despite the success of DCP
negotiations, many remain concerned about the negotiations, many remain concerned about the ~~basin~~Colorado River Basin’s long-term water supply outlook, including the potential ’s long-term water supply outlook, including the potential
for a compact for a compact ~~cal~~ call (a “call” on water rights between the Lower Basin and Upper Basinbetween the Lower Basin and Upper Basin) that might lead that might lead to a to protracted legal issues. protracted legal issues. ~~Future~~
~~water shortages due to climate~~Climate change, tribal water rights settlements, and state and local water supply change, tribal water rights settlements, and state and local water supply
development in the Upper Basin could development in the Upper Basin could ~~exacerbate these tensions~~further constrain water supplies. A central question facing the basin’s . A central question facing the basin’s
decisionmakers is whether current “interim” guidelines decisionmakers is whether current “interim” guidelines ~~wil~~ will be renewed prior to their expiration in 2026be renewed prior to their expiration in 2026, and what and what
other changes might be made as a part of those agreements. other changes might be made as a part of those agreements.
Congressional Research Service Congressional Role
Congress plays a multifaceted role in federal management of the Colorado River Basin. Congress funds and Congress plays a multifaceted role in federal management of the Colorado River Basin. Congress funds and
oversees management of basin facilities, including operations and programs to protect and restore endangered oversees management of basin facilities, including operations and programs to protect and restore endangered
species. It has enacted and continues to consider Indian water rights settlements involving Colorado River waters species. It has enacted and continues to consider Indian water rights settlements involving Colorado River waters
and development of new water storage facilities in the basin. In addition, Congress has approved funding to and development of new water storage facilities in the basin. In addition, Congress has approved funding to
mitigate water shortages and conserve basin water supplies and has enacted new authorities to combat drought mitigate water shortages and conserve basin water supplies and has enacted new authorities to combat drought
and its effects on basin water users (i.e., the DCPs and other related efforts). and its effects on basin water users (i.e., the DCPs and other related efforts).
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Tables
Table 1. 10Ten Tribes Study: Tribal Water Rights and Diversions .............................................. 1415
Table 2. Lower Basin Water Delivery Curtailment Volumes Under Existing Agreements .......... 2123

Contacts
Author Information ....................................................................................................... 2426

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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.1 The river runs through seven U.S. states (Wyoming, River Basin covers more than 246,000 square miles.1 The river runs through seven U.S. states (Wyoming,
Colorado, Utah, New Mexico, Arizona, Nevada, and California) and Mexico. Pursuant to federal law, the Colorado, Utah, New Mexico, Arizona, Nevada, and California) and Mexico. Pursuant to federal law, the
Bureau of Reclamation (Reclamation, part of the Department of the Interior [DOI]) plays a prominent role Bureau of Reclamation (Reclamation, part of the Department of the Interior [DOI]) plays a prominent role
in the management of the basin’s waters. In the Lower Basin (i.e., Arizona, Nevada, and California), 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.2 The federal role in the management of status of the federal government in basin water management.2 The federal role in the management of
Colorado River water is magnified by the multiple federal y owned and operated water storage and Colorado River water is magnified by the multiple federal y owned and operated water storage and
conveyance facilities in the basin, which provide low-cost water and hydropower supplies to water users. conveyance 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 majority (70%) of basin water supplies are used to irrigate 5.5 mil ion and recreation, among other uses. A majority (70%) of basin water supplies are used to irrigate 5.5 mil ion
acres of land; basin waters also provide M&I water supplies to nearly 40 mil ion people.3 Much of the acres of land; basin waters also provide M&I water supplies to nearly 40 mil ion people.3 Much of the
area that depends on the river for water supplies is outside of the drainage area for the Colorado River area that depends on the river for 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 Val ey in Southern California Diego, and the Imperial Val ey in Southern California (Figure 1). Colorado River hydropower facilities . Colorado River hydropower facilities
can provide up to can provide up to ~~42 gigawatts~~4200 megawatts of electrical power per year. of electrical power per year.4 The river also provides habitat for a wide The river also provides habitat for a wide
range of species, including several federal y endangered species. It flows through 7 national wildlife range of species, including several federal y endangered species. It flows through 7 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. recreational opportunities.5
Precipitation and runoff in the basin are highly variable. Water conditions on the river depend largely on Precipitation and runoff in the basin are highly variable. Water conditions on the river depend largely on
snowmelt in the basin’s northern areas. Observed snowmelt in the basin’s northern areas. Observed historical data (1906-2018) show that data (1906-2018) show that overal , natural flows in the natural flows in the
Colorado River Basin Colorado River Basin ~~in the 20th century~~ averaged about 14.8 mil ion acre-feet (MAF) annual y.averaged about 14.8 mil ion acre-feet (MAF) annual y.46 Flows Flows
have dipped significantly during the current drought, which dates to 2000; natural flows from 2000 to have dipped significantly during the current drought, which dates to 2000; natural flows from 2000 to
2018 2018 averaged approximately 12.4 MAF per year.averaged approximately 12.4 MAF per year.57 Reclamation has estimated that the 19-year period Reclamation has estimated that the 19-year period
~~from 2000 to 2018 was the driest period in more than 100 years of record keeping.6 The dry conditions~~
~~are consistent with prior droughts in the basin that were identified through tree ring studies; some of these~~
from
1 J. C. Kammerer, “Largest Rivers in the United States,” USGS Fact Sheet, May 1990, at https://pubs.usgs.gov/of/1987/ofr87-1 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. 242/pdf/ofr87242.pdf.
2 As discussed in the below section, 2 As discussed in the below section, “ T he Law of the River: Foundational Documents and Programs,” the Boulder Canyon ” the Boulder Canyon
Project Act of 1928 made the Secretary of the Interior responsible for the distribution (via contract) of all Colorado RiverProject Act of 1928 made the Secretary of the Interior responsible for the distribution (via contract) of all Colorado River water water
delivered below Hoover Damdelivered below Hoover Dam (i.e., the Lower Basin), and authorized such regulations as necessary to , and authorized such regulations as necessary to ~~enter~~ent er into these contracts. into these contracts. ~~Subsequent court~~
~~decisions~~ Subsequent court decisions confirmed the Secretary’s power to apportion surpluses and shortages among and within Lower Basinconfirmed the Secretary’s power to apportion surpluses and shortages among and within Lower Basin ~~states.~~
states; this forms the basis for the designation Lower Basin water m aster. No similar authorities and designation have been provided for the Upper Basin. 3 U.S. Bureau of Reclamation, 3 U.S. Bureau of 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. Hereinafterhttps://www.usbr.gov/lc/region/programs/crbstudy/finalreport/index.html. Hereinafter, “ Reclamation 2012 Supply/Demand “ Reclamation 2012 Supply/Demand
Study.” Study.”
4 4 Reclamation 2012 Supply/Demand Study, p. 3. 5 Reclamation 2012 Supply/Demand Study, p. 3. 6 Department of the Interior, Open Water Data Initiative, Department of the Interior, Open Water Data Initiative, Drought in the Colorado River Basin, accessed November 1, 2018, at accessed November 1, 2018, at
https://www.doi.gov/water/owdi.cr.drought/en/#SupplyDemand. https://www.doi.gov/water/owdi.cr.drought/en/#SupplyDemand.
5 7 U.S. Bureau of Reclamation, Lower Colorado Region, “Colorado River Basin Natural Flow and Salt Data-Current Natural Flow U.S. Bureau of Reclamation, Lower Colorado Region, “Colorado River Basin Natural Flow and Salt Data-Current Natural Flow
Data 1906-2016,” at http://www.usbr.gov/lc/region/g4000/NaturalFlow/current.html. Provisional natural flow measurements for Data 1906-2016,” at http://www.usbr.gov/lc/region/g4000/NaturalFlow/current.html. Provisional natural flow measurements for
2017 and 2018 by U.S. Bureau of Reclamation, Lower Colorado River Operations, at https://www.usbr.gov/lc/region/g4000/2017 and 2018 by U.S. Bureau of Reclamation, Lower Colorado River Operations, at https://www.usbr.gov/lc/region/g4000/
riverops/model-info.html. Documentation for the natural flow calculation methods is available at http://www.usbr.gov/lc/region/riverops/model-info.html. Documentation for the natural flow calculation methods is available at http://www.usbr.gov/lc/region/
~~g4000/NaturalFlow/NaturalFlowAndSaltComptMethodsNov05.pdf. Hereinafter “ Bureau of Reclamation Flow Data, 1906-2018.”~~
~~6 U.S. Bureau of Reclamation, Annual Operating Plan for Colorado River Reservoirs, 2019, September 10, 2018, p. 8.~~
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~~Management of the Colorado River: Water Allocations, Drought, and the Federal Role~~

~~droughts lasted for decades.7~~ Congressional Research Service 1 Management of the Colorado River: Water Allocations, Drought, and the Federal Role 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 droughts lasted for decades.9 Climate change impacts, including warmer temperatures and altered Climate change impacts, including warmer temperatures and altered
precipitation patterns, may further increase the likelihood of prolonged drought in the basin. 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 Pursuant to the multiple compacts, federal laws, court decisions and decrees, contracts, and regulatory
guidelines governing Colorado River operations (collectively known as the guidelines governing Colorado River operations (collectively known as the Law of the River), Congress ), Congress
and the federal government play a prominent role in the management of the Colorado River. Specifical y, and the federal government play a prominent role in the management of the Colorado River. Specifical y,
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 species. Congress has also approved facility operations and programs to protect and restore endangered species. Congress has also approved
and continues to actively consider Indian water rights settlements involving Colorado River waters, and and continues to actively 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 funding development of new and expanded water storage in the basin. In addition, Congress has approved funding
to mitigate drought and stretch basin water supplies and has considered new authorities for Reclamation to mitigate drought and stretch basin water supplies and has considered 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.

7g4000/NaturalFlow/NaturalFlowAndSaltComptMethodsNov05.pdf. Hereinafter “ Bureau of Reclamation Flow Data, 1906 -2018.” 8 U.S. Bureau of Reclamation, Annual Operating Plan for Colorado River Reservoirs, 2019, September 10, 2018, p. 8. 9 For additional discussion on historic drought in the Colorado River, see CRS Report R43407, For additional discussion on historic drought in the Colorado River, see CRS Report R43407, Drought in the United States:
Causes and Current Understanding, by Peter Folger. , by Peter Folger.
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Management of the Colorado River: Water Allocations, Drought, and the Federal Role

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

Source: Bureau of Reclamation, Bureau of Reclamation, Colorado River Basin Water Supply and Demand Study, 2012. , 2012.
The Law of the River:
Foundational Documents and Programs
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 chal enges associated with development of the Colorado River. local interests alone could not solve the chal enges associated with development of the Colorado River.
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Plans conceived by parties in California’s Imperial Val ey to divert water from the mainstream of the Plans conceived by parties in California’s Imperial Val ey 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.States and Mexico.810 The river also presented engineering chal enges, such as deep canyons and erratic The river also presented engineering chal enges, 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. Because local or state groups could not storage facilities and canals to provide an adequate water supply. Because local or state groups could not
resolve these “national problems,” Congress considered ideas to control the Colorado River and resolve resolve these “national problems,” Congress considered ideas to control the Colorado River and resolve
potential conflicts between the states. potential conflicts between the states.911 Thus, in an effort to resolve these conflicts and prevent litigation, Thus, in an effort to resolve these conflicts and prevent 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. River water supplies in 1921.1012
The below sections discuss the resulting agreement, the Colorado River Compact, and other documents The below sections discuss the resulting agreement, the Colorado River Compact, and other documents
and agreements that form the basis of the Law of the River, which governs Colorado River operations. and agreements that form the basis of the Law of the River, which governs Colorado River operations.1113
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 signed by al but one basin state (Arizona).was signed by al but one basin state (Arizona).1214 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 at Lee Ferry, AZ, between the two basins at Lee Ferry, AZ,1315 below the confluence of the Colorado and Paria Rivers near the Utah border. near the Utah border.1416 Each basin was apportioned 7.5 MAF Each basin was apportioned 7.5 MAF
annual y for beneficial consumptive use, and the Lower Basin was given the right to increase its annual y for beneficial consumptive use, and the Lower Basin was given the right to increase its
beneficial consumptive use by an additional 1 MAF annual y.beneficial consumptive use by an additional 1 MAF annual y.15 The agreement also required The agreement also required that Upper Basin Upper Basin
~~states to deliver to the Lower Basin~~states not deplete more than a total of 75 MAF over a total of 75 MAF over ~~each~~any 10-year period 10-year period (i.e., 7.5 MAF per year), thus al owing for , thus al owing for
averaging over time to make up for low-flow years.averaging over time to make up for low-flow years.1617 The compact did not address inter- or intrastate The compact did not address inter- or intrastate
al ocations of water (which it left to al ocations of water (which it left to future agreements and legislation), nor did it address water to be future agreements and legislation), nor did it address water to be
made availablemade available to Mexico, the river’s natural terminus; this matter was addressed in subsequent to Mexico, the river’s natural terminus; this matter was addressed in subsequent
international agreements. The compact was not to become binding until it had been approved by the international agreements. The compact was not to become binding until it had been approved by the
legislatures of each of the signatory states and by legislatures of each of the signatory states and by Congress. Congress.

810 Arizona v. California, 373 U.S. 546 (1963). Hereinafter “ , 373 U.S. 546 (1963). Hereinafter “ Arizona v. California.”.”
911 S. Doc. No. 67-142 (1922). For example, the states in the Upper Basin (Colorado, Wyoming, Utah, and New Mexico), where 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 athe majority of the river’s runoff originates, feared that a storage facility making water available downstream might form a basis basis
for claims by Lower Basin states (California, Arizona, and Nevada) under prior appropriation doctrine before Upper Basin for claims by Lower Basin states (California, Arizona, and Nevada) under prior appropriation doctrine before Upper Basin ~~states~~stat es
could develop means to access their share. could develop means to access their share.
1012 Ch. 72, 42 Stat. 171 (1921). In lieu of litigation, interstate compacts have historically been a preferred means of allocating Ch. 72, 42 Stat. 171 (1921). In lieu of litigation, interstate compacts have historically been a preferred means of allocating
water among competing uses. Pursuant to the U.S. Constitution, Article I, Section 10, Clause 3, no such compacts can be enter ed water among competing uses. Pursuant to the U.S. Constitution, Article I, Section 10, Clause 3, no such compacts can be enter ed
into without the consent of Congress. into without the consent of Congress.
1113 T he T he Law of the River is the commonly used shorthand for the multiple compacts, federal laws, court decisions and decrees, 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. contracts, and regulatory guidelines collectively known under this heading.
1214 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 eventually signed and ratified the compact in 1944. See below section on share of water. Arizona eventually signed and ratified the compact in 1944. See below section on “ Arizona Ratification and
Arizona v. California Decision.”
~~13 Although the compact names the point as “Lee Ferry,” it is also commonly referred to as “Lees Ferry,” or “Lees Ferry.”~~
1415 Lee Ferry is the dividing line between basins designated in the compact. Lees Ferry (or Lee’s Ferry), approximately 1 mile upstream from that point, is the location of the USGS streamgage that has measured flows dating to 1921. After the compact wa s signed, the Lees Ferry streamgage, along with a gage on the Paria River, became the measurements used to determine compliance with the compact. 16 Arizona receives water under both the Upper and the Lower Basin apportionments, since parts of the state are in both basins. Arizona receives water under both the Upper and the Lower Basin apportionments, since parts of the state are in both basins.
~~15 No such increase has been executed.~~
1617 As a result, in some years in which As a result, in some years in which ~~Upper Basin~~Lake Powell inflows are less than 7.5 MAF, less than 7.5 MAF may be available to Lower inflows are less than 7.5 MAF, less than 7.5 MAF may be available to Lower
Basin states. Basin states.
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Management of the Colorado River: Water Allocations, Drought, and the Federal Role

Boulder Canyon Project Act
Congress approved and modified the Colorado River Compact in the Boulder Canyon Project Act (BCPA) Congress approved and modified the Colorado River Compact in the Boulder Canyon Project Act (BCPA)
of 1928. of 1928.1718 The act ratified the 1922 compact, authorized the construction of a federal facility to impound 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 the Lower Basin (Boulder Dam, later renamed Hoover Dam) and related facilities to deliver
water in Southern California (e.g., the Al -American Canal, which delivers Colorado River water to water in Southern California (e.g., the Al -American Canal, which delivers Colorado River water to
California’s Imperial Val ey), and apportioned the Lower Basin’s 7.5 MAF per year among the three California’s Imperial Val ey), 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-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 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 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. 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 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 al owing the compact to become effective without ratification by California and five other states (thereby al owing 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 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 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. California Limitation Act of March 4, 1929.1819
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 Arizona did not ratify the Colorado River Compact until 1944, at which time the state began to pursue a
federal project to bring Colorado River water to its primary population centers in Phoenix and Tucson. federal project 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,California opposed the project, arguing that under the doctrine of prior appropriation,1920 California’s California’s
historical use of the river trumped Arizona’s rights to the Arizona al otment.historical use of the river trumped Arizona’s rights to the Arizona al otment.2021 California also argued that California also argued that
Colorado River apportionments under the BCPA included water developed on Colorado River tributaries, 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 whereas Arizona claimed, among other things, that these apportionments included the river’s mainstream
waters only. waters only.
In 1952, Arizona filed suit in the U.S. Supreme Court to settle the issue. Eleven years later, in the 1963 In 1952, Arizona filed suit in the U.S. Supreme Court to settle the issue. Eleven years later, in the 1963
Arizona v. California decision,decision,2122 the Supreme Court ruled in favor of Arizona, finding that Congress had the Supreme Court ruled in favor of Arizona, finding that Congress had
intended to apportion the intended to apportion the mainstream of the Colorado River and that California and Arizona each would of the Colorado River and that California and Arizona each would
receive one-half of surplus flows.receive one-half of surplus flows.2223 The same Supreme Court decision held that Section 5 of the BCPA 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 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.prior appropriation) controlled the apportionment of water among Lower Basin states.2324 The ruling was The ruling was
notable for its directive to forgo traditional Reclamation deference to state law under the Reclamation Act 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 of 1902, and formed the basis for the Secretary of the Interior’s unique role as water master for the Lower for the Lower

1718 Boulder Canyon Project Act (BCPA), Ch. 42, 45 Stat. 1057 (1928), codified as amended at 43 U.S.C. 617 . Boulder Canyon Project Act (BCPA), Ch. 42, 45 Stat. 1057 (1928), codified as amended at 43 U.S.C. 617 .
1819 T he Department of the Interior also requested that California prioritize its Colorado River rights among users before the T he Department of the Interior also requested that California prioritize its Colorado River rights among users before the
Colorado River Compact became effective; the state established priority among these users for water in both “normal” and Colorado River Compact became effective; the state established priority among these users for water in both “normal” and
“surplus” years in the California Seven-Party Agreement, signed in August 1931. “surplus” years in the California Seven-Party Agreement, signed in August 1931.
1920 Historically, water in the western United States has been governed by some form of the Historically, water in the western United States 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.
2021 Under the BCPA, Arizona and California also were to divide any excess, or surplus Under the BCPA, Arizona and California also were to divide any excess, or surplus, supplies (i.e., amounts exceeding the 7.5 supplies (i.e., amounts exceeding the 7.5
MAF basic apportionment). What was meant by the term MAF basic apportionment). What was meant by the term surplus—and how much water California could claim under this —and how much water California could claim under this
authority—was significant to the arguments in the case. authority—was significant to the arguments in the case.
2122 Arizona v. California, 373 U.S. 546 (1963). , 373 U.S. 546 (1963).
2223 Id. at 546, 573. at 546, 573.
2324 Id. at 585-586. T his decision gave the Secretary the power to apportion surpluses and shortages among and within Lower Basin at 585-586. T his decision gave the Secretary the power to apportion surpluses and shortages among and within Lower Basin
states. states.
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Basin. Basin.2425 The decision also held that Native American reservations on the Colorado River were entitled to The decision also held that Native American reservations on the Colorado River were entitled to
priority under the BCPA.priority under the BCPA.2526 Later decrees by the Supreme Court in 1964 and 1979 supplemented the 1963 Later decrees by the Supreme Court in 1964 and 1979 supplemented the 1963
decision. decision.2627
Following the Following the Arizona v. California decision, Congress eventual y authorized Arizona’s conveyance decision, Congress eventual y authorized Arizona’s conveyance
project for Colorado River water, the Central Arizona Project (CAP), in the Colorado River Basin Project project for Colorado River water, the Central Arizona Project (CAP), in the Colorado River Basin Project
Act of 1968 (CRBPA).Act of 1968 (CRBPA).2728 As a condition for California’s support of the project, Arizona agreed that, in the 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. event of shortage conditions, California’s 4.4 MAF has priority over CAP water supplies.
1944 U.S.-Mexico Water ~~Treaty28~~Treaty29
In 1944, the United States signed a water treaty with Mexico (1944 U.S.-Mexico Water Treaty) to guide In 1944, the United States signed a water treaty with Mexico (1944 U.S.-Mexico Water Treaty) to guide
how the two countries share the waters of the Colorado Riverhow the two countries share the waters of the Colorado River ~~and the Rio Grande.~~.30 The treaty established The treaty established
water al ocations water al ocations for the two countries and created a governance framework (the International Boundary for the two countries and created a governance framework (the International Boundary
and Water Commission) to resolve disputes arising from the treaty’s execution.and Water Commission) to resolve disputes arising from the treaty’s execution.29 The treaty requires the The treaty requires the
United States to provide Mexico with 1.5 MAF of United States to provide Mexico with 1.5 MAF of Colorado River water annual y, plus an additionalwater annual y, plus an additional 200,000 AF when 200,000 AF when a a
surplus is declared. During drought, the United States may reduce deliveries to Mexico in similar surplus is declared. During drought, the United States may reduce deliveries to Mexico in similar
proportion to reductions of U.S. consumptive uses. The treaty has been supplemented by additional proportion to reductions of U.S. consumptive uses. The treaty has been supplemented by additional
agreements between the United States and Mexico, known as agreements between the United States and Mexico, known as minutes~~.30~~, regarding matters related to the treaty’s execution and interpretation.31
Upper Basin Compact and Colorado River Storage Project Authorizations
Projects original y authorized for study in the Upper Basin under BCPA were not al owed to move Projects original y authorized for study in the Upper Basin under BCPA were not al owed to move
forward until the Upper Basin states determined their individual water al ocations, which they did under forward until the Upper Basin states determined their individual water al ocations, which they did under
the Upper Colorado River Basin Compact of 1948. The Upper Basin Compact established Colorado 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 (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 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 al ocations, including Wyoming~~
~~(14%), New Mexico (11.25%), and Utah (23%). Arizona was al ocated 50,000 AF in addition to its Lower~~

24 25 Pursuant to Section 8 of the Reclamation Act of 1902 (32 Stat. 388), Reclamation is not to interfere with state laws, “ Pursuant to Section 8 of the Reclamation Act of 1902 (32 Stat. 388), Reclamation is not to interfere with state laws, “~~relat ing~~relati ng to to
the control, appropriation, use, or distribution of water used in irrigation” and that “the Secretary of the Interior, in car rying out the control, appropriation, use, or distribution of water used in irrigation” and that “the Secretary of the Interior, in car rying out
provisions of the Act, shall proceed in conformance with such laws.” provisions of the Act, shall proceed in conformance with such laws.”
2526 Indian reserved water rights were first recognized by the Supreme Court in Indian reserved water rights were first recognized by the Supreme Court in Winters v. United States in 1908. in 1908. Winters v. United
States, 207 U.S. 564, 575-77 (1908). Under the , 207 U.S. 564, 575-77 (1908). Under the Winters doctrine, when Congress reserves land (i.e., for an Indian reservation), it 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, 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 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 rights of tribes often are senior to those of non-Indian water rights. For more information on the resulting settlements, see below
section on section on “ T ribal Water Rights” and CRS Report R44148, and CRS Report R44148, Indian Water Rights Settlements, by Charles V. Stern. , by Charles V. Stern.
2627 Arizona v. California,, 376 U.S. 340, 341 (1964). T he 1964 decree determined, among other things, that all water in the 376 U.S. 340, 341 (1964). T he 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.” T he 1979 supplemental decree shortage.” T he 1979 supplemental decree ~~det ermined~~determined the present perfected rights of various parties in the Lower Basin. the present perfected rights of various parties in the Lower Basin.
2728 Colorado River Basin Project Act of 1968, P.L. 90-537. Colorado River Basin Project Act of 1968, P.L. 90-537.
2829 For more information on the 1994 U.S.-Mexico Water T reaty and Colorado River water sharing issues with Mexico, see CRS For more information on the 1994 U.S.-Mexico Water T reaty 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.
29 30 T he treaty also included water-sharing provisions relating to the Lower Rio Grande and T ijuana Rivers. See T reaty Between the United States of America and Mexico Respecting Utilization of W aters of the Colorado and T ijuana Rivers T reaty Between the United States of America and Mexico Respecting Utilization of W aters of the Colorado and T ijuana Rivers
and of the Rio Grande, U.S.-Mex., Februaryand of the Rio Grande, U.S.-Mex., February 3, 1944, 59 State. 1219, at https://www.ibwc.gov/T reaties_Minutes/treaties.html. 3, 1944, 59 State. 1219, at https://www.ibwc.gov/T reaties_Minutes/treaties.html.
~~T he United States ratified the treaty on November 1, 1945, and Mexico ratified it on October 16~~Mexico ratified it on October 16, 1945 and the United States ratified the treaty on November 1, 1945. It became effective on, 1945. It became effective on
~~November~~ Nove mber 8, 1945. 8, 1945.
30 31 T he complete list of minutes is available at https://www.ibwc.gov/T reaties_Minutes/Minutes.html. For more information on T he complete list of minutes is available at https://www.ibwc.gov/T reaties_Minutes/Minutes.html. For more information on
recent minutes, see below section, recent minutes, see below section, “ Minute 319 and Minute 323 Agreements with Mexico.”
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Lower Basin have been met. Other states also received percentage-based al ocations, including Wyoming (14%), New Mexico (11.25%), and Utah (23%).32 Arizona was al ocated 50,000 AF in addition to its Lower Basin apportionment, in recognition of the smal portion of the state in the Upper Basin. Basin al ocations Basin apportionment, in recognition of the smal portion of the state in the Upper Basin. Basin al ocations
by state following approval of the Upper Basin Compact (i.e., the al ocations that general y guide current by state following approval of the Upper Basin Compact (i.e., the al ocations that general y guide current
water deliveries) are shown below iwater deliveries) are shown below in Figure 2. The Upper Basin Compact also established the Upper The Upper Basin Compact also established the Upper
Colorado River Commission, Colorado River Commission, ~~which coordinates operations and positions among Upper Basin states~~
~~Figure 2. Colorado River Basin Allocations~~
~~percentages of overal al ocation and mil ion acre-feet (MAF~~an interstate administrative water agency charged with administering the provisions of the Upper Basin Compact.33 32 T here was uncertainty about how much water would remain in the Upper Basin after Colorado River Compact obligations to Lower Basin states were fulfilled. T herefore, 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 33 For more information, see http://www.ucrcommission.com/about-us/. Congressional Research Service 7 Management of the Colorado River: Water Allocations, Drought, and the Federal Role Figure 2. Colorado River Basin Allocations (percentages of overal al ocation and mil ion 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.
Notes: Although both the Upper and Lower Basins were al ocated 7.5 MAF, there was uncertainty about how much Although both the Upper and Lower Basins were al ocated 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. 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 annual y to Arizona, the Upper Basin Compact Therefore, outside of 50,000 AF provided annual y to Arizona, the Upper Basin Compact ~~provides its~~includes apportionments in apportionments in
terms of percentage of the overal Upper Basin al ocation. terms of percentage of the overal Upper Basin al ocation.
Subsequent federal legislation paved the way for development of Upper Basin al ocations. The Colorado Subsequent federal legislation paved the way for development of Upper Basin al ocations. The Colorado
River Storage Project (CRSP) Act of 1956 authorized storage reservoirs and dams in the Upper Basin, 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 including the Glen Canyon, Flaming Gorge, Navajo, and Curecanti Dams. The act also established the
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Upper Colorado River Basin Fund, which receives revenues collected in connection with the projects, to 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 be made available for defraying the project’s costs of operation, maintenance, and emergency
expenditures. expenditures.
In addition to the aforementioned authorization of CAP in Arizona, the 1968 CRBPA amended CRSP to In addition to the aforementioned authorization of CAP in Arizona, the 1968 CRBPA amended CRSP to
authorize several additional Upper Basin projects (e.g., the Animas La Plata and Central Utah projects) as authorize several additional Upper Basin projects (e.g., the Animas La Plata and Central Utah projects) as
Congressional Research Service 8 Management of the Colorado River: Water Allocations, Drought, and the Federal Role CRSP participating projects. It also directed that the Secretary of the Interior propose operational criteria 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 Powel ) that prioritize for Colorado River Storage Project units (including the releases of water from Lake Powel ) that prioritize
(1) (1) ~~Treaty Obligations~~treaty obligations to Mexico, (2) the Colorado River Compact requirement for the Upper Basin to to Mexico, (2) the Colorado River Compact requirement for the Upper Basin to
~~deliver~~not deplete more than 75 MAF to Lower Basin states over any 10-year period 75 MAF to Lower Basin states over any 10-year period (i.e., 7.5 MAF per year), and (3) carryover storage to meet these , and (3) carryover storage to meet these
needs. The CRBPA also established the Upper Colorado River Basin Fund and the Lower Colorado River 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 Basin Development Fund, both of which were authorized to utilize revenues from power generation from revenues from power generation from
relevant Upper and Lower Basin facilities to fund certain expenses relevant Upper and Lower Basin facilities to fund certain expenses in the sub-basins.in the sub-basins.3134
Water Storage and Operations
Due to the basin’s large water storage projects, basin water users are able to store as much as 60 MAF, or Due to the basin’s large water storage projects, basin water users are able to store as much as 60 MAF, or
about four times the Colorado River’s annual flows. Thus, storage and operations in the basin receive about four times the Colorado River’s annual flows. 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 Powel in the Upper Basin (26.2 MAF of storage capacity) and Hoover Dam/Lake Canyon Dam/Lake Powel in the Upper Basin (26.2 MAF of storage capacity) and Hoover Dam/Lake
Mead in the Lower Basin (26.1 MAF). The status of these projects is of interest to basin stakeholders and Mead in the Lower Basin (26.1 MAF). The status of these projects is of interest to basin stakeholders and
observers and is monitored closely by Reclamation. observers and is monitored closely by Reclamation.
Glen Canyon Dam, completed in 1963, serves as the linchpin for Upper Basin storage and regulates flows Glen Canyon Dam, completed in 1963, 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. It also generates from the Upper Basin to the Lower Basin, pursuant to the Colorado River Compact. It also generates
approximately 5 bil ion kilowatt hours (KWh) of electricity per year, which the Western Area Power approximately 5 bil ion kilowatt hours (KWh) of electricity per year, which the Western Area Power
Administration (WAPA) supplies to 5.8 mil ion customers in Upper Basin States.Administration (WAPA) supplies to 5.8 mil ion customers in Upper Basin States.3235 Other significant Other significant
storage in the Upper Basin includes the initial “units” of the CRSP: the Aspinal Unit in Colorado storage in the Upper Basin includes the initial “units” of the CRSP: the Aspinal 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),3336 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 3.78 MAF), and the Navajo Unit in New Mexico (including Navajo Dam Green River, with a capacity of 3.78 MAF), and the Navajo Unit in New Mexico (including Navajo Dam
on the San Juan River, with a capacity of 1 MAF). The Upper Basin is also home to 16 “participating” on the San Juan River, with a capacity of 1 MAF). The Upper Basin is also home to 16 “participating”
projects which are authorized to use water for irrigation, municipal and industrial uses, and other projects which are authorized to use water for irrigation, municipal and industrial uses, and other
purposes. purposes.3437
In the Lower Basin, Hoover Dam, completed in 1936, provides the majority of the Lower Basin’s storage In the Lower Basin, Hoover Dam, completed in 1936, provides the majority of the Lower Basin’s storage
and generates about 4.2 bil ion KWh of electricity per year for customers in California, Arizona, and and generates about 4.2 bil ion KWh of electricity per year for customers in California, Arizona, and
Nevada.Nevada.3538 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 al owing for deliveries to urban areas in southern California) and CAP (al owing for diversion to users in Arizona). Further downstream on the Arizona/California border, Imperial Dam (a diversion dam) diverts Colorado River water to the Al - American Canal for use in California’s Imperial and Coachel a Val eys. 34
31 Basin-wide operational commitments on the Colorado River were established in the 1970 Criteria for Coordinated Long-Range Basin-wide operational commitments on the Colorado River were established in the 1970 Criteria for Coordinated Long-Range
Operation of Colorado River Reservoirs, Operation of Colorado River Reservoirs, ~~which coordinat ed~~wh ich coordinated the operation of reservoirs in the Upper and Lower Basins, including the operation of reservoirs in the Upper and Lower Basins, including
releases from Lake Powell and Lake Mead. T hese operating instructions have been modified by more recent operational releases from Lake Powell and Lake Mead. T hese operating instructions have been modified by more recent operational
agreements intended to mitigate the effects of long-term drought. agreements intended to mitigate the effects of long-term drought.
3235 Bureau of Reclamation, Upper Colorado Region, “ Glen Canyon Unit,” accessed February 21, 2019, https://www.usbr.gov/uc/ Bureau of Reclamation, Upper Colorado Region, “ Glen Canyon Unit,” accessed February 21, 2019, https://www.usbr.gov/uc/
rm/crsp/gc/. rm/crsp/gc/.
3336 T he Curecanti Unit was renamed the Aspinall Unit in 1980 in T he Curecanti Unit was renamed the Aspinall Unit in 1980 in ~~h onor~~honor of U.S. Representative Wayne N. Aspinall of Colorado. of U.S. Representative Wayne N. Aspinall of Colorado.
34 37 In total, 16 of the 22 Upper Basin projects authorized as part of CRSP have been developed. (Of the six remaining projects, 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 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. deleted by Congress.) For a complete list of projects, see https://www.usbr.gov/uc/rm/crsp/index.html.
3538 Bureau of Reclamation, “Hoover Dam Frequently Asked Questions and Answers,” accessed February 21, 2019, Bureau of Bureau of Reclamation, “Hoover Dam Frequently Asked Questions and Answers,” accessed February 21, 2019, Bureau of
Reclamation, Upper Colorado Region, Reclamation, Upper Colorado Region, Glen Canyon Unit, accessed February 21, 2019, https://www.usbr.gov/uc/rm/crsp/gc/. , accessed February 21, 2019, https://www.usbr.gov/uc/rm/crsp/gc/.
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~~diversion into the Colorado River Aqueduct (thereby al owing for deliveries to urban areas in southern~~
~~California) and CAP (al owing for diversion to users in Arizona). Further downstream on the~~
~~Arizona/California border, Imperial Dam (a diversion dam) diverts Colorado River water to the Al -~~
~~American Canal for use in California’s Imperial and Coachel a Val eys.~~
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 (cal ed monthly studies (cal ed 24-month studies). The studies take into account forecasted hydrology, reservoir ). 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 Powel in terms of elevation, as feet future. They express water storage conditions at Lake Mead and Lake Powel in terms of elevation, as feet
(ft) above mean sea level. (ft) above mean sea level.
In addition to the 24-month studies, the CRBPA requires the Secretary to transmit to Congress and the In addition to the 24-month studies, the CRBPA requires the Secretary to transmit to Congress and the
governors of the basin states, by January 1 of each year, a report describing the actual operation for the governors of the basin states, by January 1 of each year, a report describing the actual operation for the
preceding water year and the projected operation for the coming year. This report is commonly referred to preceding water year and the projected operation for the coming year. This report is commonly referred to
as the as the annual operating plan (AOP). The AOP’s projected January 1 water conditions for the upcoming (AOP). 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.3639
Since the adoption of new operational guidelines by Reclamation and basin states in 2007 (see below Since the adoption of new operational guidelines by Reclamation and basin states in 2007 (see below
section, section, “2007 Interim Guidelines”), operations of the Hoover and Glen Canyon Dams have been tied to ), operations of the Hoover and Glen Canyon Dams have been tied to
specific pool elevations at Lake Mead and Lake Powel . For Lake Mead, the first level of shortage (a specific pool elevations at Lake Mead and Lake Powel . For Lake Mead, the first level of shortage (a
““~~Tier~~Level One” Shortage Condition) in the original 2007 guidelines, under which Arizona and Nevada’s One” Shortage Condition) in the original 2007 guidelines, under which Arizona and Nevada’s
al ocations are decreased, would be triggered if Lake Mead were to fal below 1,075 ft. Subsequently, a al ocations are decreased, would be triggered if Lake Mead were to fal below 1,075 ft. Subsequently, a
new new ~~“Tier Zero” that includes~~set of curtailments for Nevada and Arizona curtailments for Nevada and Arizona at lake elevations up to 1,090 ftat lake elevations up to 1,090 ft (“Tier Zero”) was was
added added pursuant to the 2019 Drought Contingency Plan for the Lower Colorado River Basin.pursuant to the 2019 Drought Contingency Plan for the Lower Colorado River Basin.3740 (See below (See below
section, section, “2019 Drought Contingency Plans.”) For Lake Powel , releases under tiered operations are based ”) For Lake Powel , releases under tiered operations are based
on storage levels in both Lake Powel and Lake Mead. on storage levels in both Lake Powel and Lake Mead.3841
Recent reductions in water consumption and deliveries, coupled with marginal improvements in Recent reductions in water consumption and deliveries, coupled with marginal improvements in
hydrology in some years, have decreased the likelihood of hydrology in some years, have decreased the likelihood of major delivery curtailments (i.e., a Tier One or delivery curtailments (i.e., a Tier One or
greater shortage) in the immediate future.greater shortage) in the immediate future.3942 As of August 2020, Reclamation predicted that over the As of August 2020, Reclamation predicted that over the
upcoming 24 months, Lake Mead’s elevation was likely to remain above 1,075 ft (approximately 9.6 upcoming 24 months, Lake Mead’s elevation was likely to remain above 1,075 ft (approximately 9.6
MAF of storage) but below 1,090 ft (i.e., in Tier Zero), and Lake Powel ’s elevation would remain at or MAF of storage) but below 1,090 ft (i.e., in Tier Zero), and Lake Powel ’s elevation would remain at or
near current levels (i.e., the Upper Elevation Balancing Tier).near current levels (i.e., the Upper Elevation Balancing Tier).4043 In its August 2020 study, Reclamation In its August 2020 study, Reclamation
projected a 23% chance of additional curtailments (beyond Tier Zero) through 2022 and a 49% chance of projected a 23% chance of additional curtailments (beyond Tier Zero) through 2022 and a 49% chance of
additional cutbacks by 2024, depending on the hydrology assumed.additional cutbacks by 2024, depending on the hydrology assumed.4144 This is an improvement from early This is an improvement from early
2019, when Reclamation projected a 69% chance of a shortage condition by the end of 2020. 2019, when Reclamation projected a 69% chance of a shortage condition by the end of 2020.4245

3639 Current and historical AOPs are available at https://www.usbr.gov/uc/water/rsvrs/ops/aop/. Current and historical AOPs are available at https://www.usbr.gov/uc/water/rsvrs/ops/aop/.
3740 Curtailed deliveries to Mexico at the same reservoir levels were also included under a separate agreement. See below section, Curtailed deliveries to Mexico at the same reservoir levels were also included under a separate agreement. See below section,
“Minute 319 and Minute 323 Agreements with Mexico.”
3841 Unlike Lake Mead, specific delivery curtailments to states based on lake levels have not been adopted for Lake Powell. Unlike Lake Mead, specific delivery curtailments to states based on lake levels have not been adopted for Lake Powell.
3942 As discussed later in this report, under current guidelines, delivery curtailments under T ier One would be approximately 2.5 As discussed later in this report, under current guidelines, delivery curtailments under T ier One would be approximately 2.5
times greater than those under T ier Zero. times greater than those under T ier Zero.
4043 Bureau of Reclamation, Bureau of Reclamation, Draft Annual Operating Plan for Colorado River Reservoirs, 2021 , August 2020. , August 2020.
4144 Bureau of Reclamation, Bureau of Reclamation, Percent of Traces with Event or System Condition. Results from ~~August 20 20~~Augu st 2020, accessed September 25, , accessed September 25,
2020, at https://www.usbr.gov/lc/region/g4000/riverops/crss-5year-projections.html. Hereinafter, “ 2020 Colorado River 2020, at https://www.usbr.gov/lc/region/g4000/riverops/crss-5year-projections.html. Hereinafter, “ 2020 Colorado River
Modeling.” Modeling.”
4245 Bureau of Reclamation, Bureau of Reclamation, Colorado River System 5-Year Projected Future Conditions, accessed November 1, 2018, at , accessed November 1, 2018, at
https://www.usbr.gov/lc/region/g4000/riverops/crss-5year-projections.html. https://www.usbr.gov/lc/region/g4000/riverops/crss-5year-projections.html.
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Figure 3. Lake Powell and Lake Mead Elevations and Operational Tiers
(as of fal 2020as of fal 2020)

Source: Figure by CRS, based onFigure by CRS, based on Bureau of Reclamation data and information in the 2007 Interim Guidelines and the Bureau of Reclamation data and information in the 2007 Interim Guidelines and the
2019 Drought Contingency Plan for the Lower Basin. 2019 Drought Contingency Plan for the Lower Basin.
Notes: Depicts January 1 elevations for each year Depicts January 1 elevations for each year~~. Pursuant to the 2019 Lower Basin Drought Contingency Plan,~~
~~California would begin to curtail its deliveries at Tier 2b (i.e., 200,000 AF), with curtailments increasing by 50,000 AF for~~
~~each five feet reduction of Lake Mead elevation until Tier 3 is reached. Pursuant to the Binational Water Scarcity~~
~~Contingency Plan, Mexico would also curtail its deliveries by increasing amounts under Tier 2b~~. For more information on . For more information on
delivery curtailments, seedelivery curtailments, see Table 2.
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). Thus, ) and the Endangered Species Act (ESA; 87 Stat. 884, 16 U.S.C. §§1531-1544). 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
original y taken into account. Over time, multiple efforts have been initiated to mitigate these effects. original y 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 species. and the effects of facility operations on endangered species.
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Salinity Control
Salinity and water quality are long-standing issues in the Colorado River Basin. Parts of the Upper Basin Salinity and water quality are long-standing issues in the Colorado River Basin. Parts of the Upper Basin
are covered by salt-bearing shale (which increases salt content in water inflows), and salinity content are covered by salt-bearing shale (which increases salt content in water inflows), and salinity content
Congressional Research Service 11 Management of the Colorado River: Water Allocations, Drought, and the Federal Role 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. However, after years of dispute between the United States and Mexico regarding Colorado River Basin. However, after years of dispute between the United States and Mexico regarding
the salinity of the water reaching Mexico’s border, the two countries reached an agreement on August 30, 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.4346 The The
agreement guarantees Mexico that the average salinity of its treaty deliveries wil be no more than 115 agreement guarantees Mexico that the average salinity of its treaty deliveries wil be no more than 115
parts per mil ion higher than the salt content of the water diverted to the Al -American Canal at Imperial parts per mil ion higher than the salt content of the water diverted to the Al -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 (P.L. 93-320), which agreement, Congress passed the Colorado River Basin Salinity Control Act of 1974 (P.L. 93-320), 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 capacity.never operated at capacity.4447 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.4548
Endangered Species Efforts and Habitat Improvements
Congress enacted the ESA in 1973.Congress enacted the ESA in 1973.4649 As basin species became listed in accordance with the act, As basin species became listed in accordance with the act,4750 federal federal
agencies and nonfederal stakeholders consulted with the U.S. Fish and Wildlife Service (FWS) to address 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 consultations, several major programs have been the conservation of the listed species. As a result of these consultations, several major programs have been
developed to protect and restore developed to protect and restore endangered fish species on the Colorado River and its tributaries. fish species on the Colorado River and its tributaries. Summaries of some Summaries of some
of the key programs are below. of the key programs are below.
Upper Colorado Endangered Fish Recovery Program
The Upper Colorado Endangered Fish Recovery Program was established in 1988 to assist in the recovery The Upper Colorado Endangered Fish Recovery Program was established in 1988 to assist in the recovery
of four species of endangered fish in the Upper Colorado River Basin.of four species of endangered fish in the Upper Colorado River Basin.4851 Congress authorized this program Congress authorized this program
in P.L. 106-392. The program is implemented through several stakeholders under a cooperative agreement 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 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 recovery goals of the program are to reduce threats to species and improve their status so they are
eventual y 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 agency for the program and provides the majority of federal funds for implementation. It is also funded 46
43 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/T reaties_Minutes/Minutes.html. , August 30, 1973, at https://www.ibwc.gov/T reaties_Minutes/Minutes.html.
4447 T he Yuma Desalting Plant’s limited operations have been due in part to the cost of its operations (desalination can require T he 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 Riverconsiderable electricity to operate) and surplus flows in the Colorado River during some years compared to what was expected. 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 intoMexico and disposed of through a canal that enters Mexico and discharges into wetlands called the Ciénega de Santa Clara, near wetlands called the Ciénega de Santa Clara, near
the Gulf of California. Whether and how the plant should be operated, and how the impacts on the Ciénega de Santa Clara from the Gulf of California. Whether and how the plant should be operated, and how the impacts on the Ciénega de Santa Clara from
the untreated irrigation runoff should be managed, remain topics of some debate in the basin and between Mexico and the United the untreated irrigation runoff should be managed, remain topics of some debate in the basin and between Mexico and the United
States. States.
4548 Additional information about the forum and related salinity control efforts is available at Colorado River Basin, Salinity Additional information about the forum and related salinity control efforts is available at Colorado River Basin, Salinity
Control Forum, at https://www.coloradoriversalinity.org/. Control Forum, at https://www.coloradoriversalinity.org/.
4649 For more information on the ESA, see CRS Report RL31654, For more information on the ESA, see CRS Report RL31654, The Endangered Species Act: A Primer, by Pervaze A. Sheikh. , by Pervaze A. Sheikh.
4750 Several endangered species are Several endangered species are found throughout the Colorado River Basin. Some are specifically found in the Colorado River, such throughout the Colorado River Basin. Some are specifically found in the Colorado River, such
as as the Razorback sucker (the Razorback sucker (Xyrauchen texanus), Bonytail chub (), Bonytail chub (Gila elegans), Colorado pikeminnow (), Colorado pikeminnow (Ptychocheilus Lucius), and ), and
Humpback chub (Humpback chub (Gila cypha). ).
4851 For more information, see Upper Colorado River Endangered Fish Recovery Program at For more information, see Upper Colorado River Endangered Fish Recovery Program at
http://www.coloradoriverrecovery.org/. http://www.coloradoriverrecovery.org/.
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~~eventual y 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~~
~~agency for the program and provides the majority of federal funds for implementation. It is also funded~~
through a portion of Upper Basin hydropower revenues from WAPA; FWS; the states of Colorado, through a portion of Upper Basin hydropower revenues from WAPA; 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.~~49 The program~~
52 The program is a partnership implemented under a cooperative agreement between the Department of the Interior and the states of Colorado and New Mexico, the Jicaril a Apache Nation, the Navajo Nation, the Southern Ute Indian Tribe, and the Ute Mountain Ute Indian Tribe.53 It is concerned with the recovery of the Razorback sucker (is concerned with the recovery of the Razorback sucker (Xyrauchen texanus) and Colorado pikeminnow ) and Colorado pikeminnow
((Ptychocheilus Lucius). Congress authorized this program in P.L. 106-392 with the aim to protect the ). Congress authorized this program in P.L. 106-392 with the aim to protect the
genetic integrity and population of listed species, conserve and restore habitat (including water quality), genetic integrity and population of listed species, conserve and restore habitat (including water quality),
reduce nonnative species, and monitor species. The reduce nonnative species, and monitor species. The Recovery Program is coordinated by FWS. Recovery Program is coordinated by FWS.
Reclamation is responsible for operating the Animas-La Plata Project and Navajo Dam on the San Juan Reclamation is responsible for operating the Animas-La Plata Project and Navajo Dam on the San Juan
River in a way that reduces effects on the fish populations. The program is funded by a portion of River in a way that reduces effects on the fish populations. The program is funded by a portion of
revenues from power generation, Reclamation, participating states, and the Bureau of Indian Affairs. revenues from power generation, Reclamation, participating states, and the Bureau of Indian Affairs.
Recovery efforts for listed fish are coordinated with the Upper Colorado Recovery efforts for listed fish are coordinated with the Upper Colorado River Program discussed above. 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 (P.L. 102-575) to operate Glen Canyon from Congress under the Grand Canyon Protection Act of 1992 (P.L. 102-575) 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.”5054 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.monitoring and other studies to evaluate the effects of the flows.55 The results are expected to better inform The results are expected to better inform
managers how to provide water deliveries and conserve species. The majority of program funding managers how to provide water deliveries and conserve species. The majority of program funding ~~comes~~
comes from hydropower revenues generated at Glen Canyon Dam. from hydropower revenues generated at Glen Canyon Dam.
Lower Colorado Multi-Species Conservation Program (MSCP)
The MSCP is a multistakeholder initiative to conserve 27 species (8 listed under ESA) along the Lower The 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 Colorado River while maintaining water and power supplies for farmers, tribes, industries, and urban
residents.residents.5156 The MSCP began in 2005 and is planned to last for at least 50 years. The MSCP began in 2005 and is planned to last for at least 50 years.5257 The MSCP was created The MSCP was created
through consultation under ESA. To achieve compliance under ESA, federal entities involved in through consultation under ESA. To achieve compliance under ESA, federal entities involved in
managing water supplies in the Lower Colorado River managing water supplies in the Lower Colorado River Basin met with resource agencies from Arizona, met with resource agencies from Arizona,
California, and Nevada; Native American Tribes; environmental groups; and recreation interests to 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 biological opinion (BiOp) develop a program to conserve species along a portion of the Colorado River. A 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~~

4952 For more information, see San Juan River Basin Recovery Implementation Program at https://www.fws.gov/southwest/sjrip/. For more information, see San Juan River Basin Recovery Implementation Program at https://www.fws.gov/southwest/sjrip/.
5053 It also includes participation by water development interests in Colo rado and New Mexico. 54 For more information, see Bureau of Reclamation, Glen Canyon Dam Adaptive Management Program, “Glen Canyon Dam For more information, see Bureau of Reclamation, Glen Canyon Dam Adaptive Management Program, “Glen Canyon Dam
High Flow Experimental Release,” at https://www.usbr.gov/uc/rm/gcdHFE/. High Flow Experimental Release,” at https://www.usbr.gov/uc/rm/gcdHFE/.
5155 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. 56 T he stakeholders include six federal and state agencies, six tribes, and 36 cities and water and power authorities. Stakeholders T he 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 serve more than 20 million residents in the region, and irrigate ~~two~~2 million acres of farmland. For more information, see Lower million acres of farmland. For more information, see Lower
Colorado River Multi-Species Conservation Program at https://www.lcrmscp.gov/. Colorado River Multi-Species Conservation Program at https://www.lcrmscp.gov/.
5257 T he program was formally authorized by Congress under Subtitle E of T itle IX of P.L. 111-11. T he program was formally authorized by Congress under Subtitle E of T itle IX of P.L. 111-11.
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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 permit under Section 10(a) of the ESA for their activities in 2005 and shortly thereafter implemented a
habitat conservation plan. habitat conservation plan.
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 mil ion in 2003 dollars ($882 mil ion in 2018 dollars) and is to be over its lifetime is approximately $626 mil ion in 2003 dollars ($882 mil ion in 2018 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%).5358 The management and implementation of the MSCP is the The management and implementation of the MSCP is the
responsibility of Reclamation, in consultation with a steering committee of stakeholders. responsibility of Reclamation, in consultation with a steering committee of stakeholders.
Hydropower Revenues Funding Colorado River Basin Activities
Hydropower revenues finance a number of activities throughout the Colorado River Basin. In the Lower Basin, the Hydropower revenues finance a number of activities throughout the Colorado River Basin. In the Lower Basin, the
Colorado River Dam fund uses power revenues generated by the Boulder Canyon Project (i.e., Hoover Dam) to fund Colorado River Dam fund uses power revenues generated by the Boulder Canyon Project (i.e., Hoover Dam) to fund
operational and construction costs for related Reclamation facilities. A separate fund, the Lower Colorado River Basin operational and construction costs for related Reclamation facilities. A separate fund, the Lower Colorado River Basin
Development Fund, col ects revenues from the Central Arizona Project (CAP), as wel as a surcharge on revenues from the Development Fund, col ects revenues from the Central Arizona Project (CAP), as wel as a surcharge on revenues from the
Boulder Canyon and Parker-Davis Projects that was enacted under the Hoover Power Plant Act of 1984 (P.L. 98-381). 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 control efforts, and funding for Indian water rights settlements identified under the ~~Arizona~~Ariz ona Water Settlements Act of 2004 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-two federal y recognized tribes in the Colorado River Basin have quantified water diversion Twenty-two federal y recognized tribes in the Colorado River Basin have quantified water diversion
rights that have been confirmed by court decree or final settlement. These tribes collectively possess rights that have been confirmed by court decree or final settlement. These tribes collectively possess
rights to 2.9 MAF per year of Colorado River water.rights to 2.9 MAF per year of Colorado River water.~~54 However, as~~59 As of 2015, these tribes typical y were of 2015, these tribes typical y were
using just over half of their quantified rights.using just over half of their quantified rights.5560 Additional y, 13 other basin tribes have reserved water Additional y, 13 other basin tribes have reserved water
rights claims rights claims that have yet to be resolved, although the total potential amount of these claims has not been that have yet to be resolved, although the total potential amount of these claims has not been
estimated.estimated.56 61 Increased water use by tribes with existing water rights, and/or future settlement of claims Increased water use by tribes with existing water rights, and/or future settlement of claims
and additionaland additional consumptive use of basin waters by other tribes, is likely to exacerbate the competition for consumptive use of basin waters by other tribes, is likely to exacerbate the competition for
basin water basin water resources. resources.
The potential for increased use of tribal water rights (which, once ratified, are counted toward state- The potential for increased use of tribal water rights (which, once ratified, are counted toward state-
specific al ocations where the tribal reservation is located) has been studied in recent years. In 2014, specific al ocations where the tribal reservation is located) has been studied in recent years. In 2014,
Reclamation, working with a group of 10 tribes with significant reserved water rights claims on the 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.57 The study, published in 2018, estimated~~

53 58 As of the end of 2018, more than $295 million had been spent on program implementation. Lower Colorado River Multi - As of the end of 2018, more than $295 million had been spent on program implementation. Lower Colorado River Multi -
Species Conservation Program, “Species Conservation Program, “ Funding,” https://www.lcrmscp.gov/steer_committee/funding.html. Accessed February 22, Funding,” https://www.lcrmscp.gov/steer_committee/funding.html. Accessed February 22,
2019. 2019.
5459 Reclamation 2012 Supply/Demand Study, T echnical Report C, Reclamation 2012 Supply/Demand Study, T echnical Report C, ~~App endix~~Appendix C9, p. C9 C9, p. C9 -4. -4.
5560 Colorado River Research Group, Colorado River Research Group, Tribes and Water in the Colorado River Basin, June 2016, at June 2016, at
https://www.coloradoriverresearchgroup.org/uploads/4/2/3/6/42362959/crrg_tribal_water_rights.pdf. According to this study, https://www.coloradoriverresearchgroup.org/uploads/4/2/3/6/42362959/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 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. diversion rights.
5661 Colorado River Research Group, Colorado River Research Group, Tribes and Water in the Colorado River Basin, June 2016, at June 2016, at
https://www.coloradoriverresearchgroup.org/uploads/4/2/3/6/42362959/crrg_tribal_water_rights.pdf.https://www.coloradoriverresearchgroup.org/uploads/4/2/3/6/42362959/crrg_tribal_water_rights.pdf.
~~57 T he tribes are the Chemehuevi Indian T ribe, Cocopah Indian T ribe, Colorado River Indian T ribes, Fort Mojave Indian T ribe,~~
~~Jicarilla Apache Nation, Navajo Nation, Quechan Indian T ribe, Southern Ute Indian T ribe, Ute Indian T ribe, and Ute Mountain~~
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Colorado River, initiated a study known as the 10 Tribes Study.62 The study, published in 2018, estimated that, cumulatively, the 10 tribes in the study could have reserved water rights (including unresolved that, cumulatively, the 10 tribes in the study could have reserved water rights (including unresolved
claims) to divert nearly 2.8 MAF per year.claims) to divert nearly 2.8 MAF per year.5863 Of these water rights, approximately 2 MAF per year were 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) confirmed by a court decree or final settlement and an additional 785,273 AF (mostly in the Upper Basin)
remained unresolved.remained unresolved.5964 The report estimated that, overal , the 10 tribes are diverting (i.e., making use of) The report estimated that, overal , the 10 tribes are diverting (i.e., making use of)
almost 1.5 MAF of their 2.8 MAF in resolved and unresolved claims.almost 1.5 MAF of their 2.8 MAF in resolved and unresolved claims. Table 1 shows these figures at the shows these figures at the
basin and sub-basin levels.basin and sub-basin levels.6065 According to the study, the majority of unresolved claims among the 10 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 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). Nation in Utah (314,926 AF), and the Navajo Nation in the Upper Basin in Arizona (77,049 AF).
Table 1. 10Ten Tribes Study: Tribal Water Rights and Diversions
(values in terms of acre-feet per yearvalues in terms of acre-feet per year)
Current Use

Reserved/Settled
Unresolved Water
Total Estimated

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

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

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

2,012,971
785,273
2,798,244
Source: U.S. Bureau of Reclamation, Colorado River Ten Tribes Partnership, U.S. Bureau of Reclamation, Colorado River Ten Tribes Partnership, Colorado River Basin Ten Tribes Partnership
Tribal Water Study, Study Report, December 2018. Study Report, December 2018.
Note: Unresolved water rights include claims for potential water rights that have yet to be resolved. : Unresolved water rights include claims for potential water rights that have yet to be resolved.
Drought and the Supply/Demand Imbalance in the
Colorado River Basin
When the Colorado River Compact was original y approvedWhen the Colorado River Compact was original y approved in 1922, it was assumed based on the historical , it was assumed based on the historical
record that average annual flows on the river were 16.4 MAF per year.record that average annual flows on the river were 16.4 MAF per year.6166 According to Reclamation data, According to Reclamation data,
from 1906 to 2018, observedfrom 1906 to 2018, observed historical natural flows on the river at Lee Ferry, AZ—the common point of natural flows on the river at Lee Ferry, AZ—the common point of
measurement for observed basin flows—averaged 14.8 MAF annual y.measurement for observed basin flows—averaged 14.8 MAF annual y.6267 Natural flows from 2000 to 2018 Natural flows from 2000 to 2018
(i.e., during the ongoing drought) averaged considerably less than that—12.4 MAF annual y.(i.e., during the ongoing drought) averaged considerably less than that—12.4 MAF annual y.63
68 Consumptive use and losses in the basin have grown and has regularly exceeded natural flows, Consumptive use and losses in the basin have grown and has regularly exceeded natural flows, in in
particular during the current drought.particular during the current drought.6469 From 1971 to 2002, total consumptive use and losses grew from From 1971 to 2002, total consumptive use and losses grew from

~~Ute T ribe.~~
58 62 T he tribes are the Chemehuevi Indian T ribe, Cocopah Indian T ribe, Colorado River Indian T ribes, Fort Mojave Indian T ribe, Jicarilla Apache Nation, Navajo Nation, Quechan Indian T ribe, Southern Ute Indian T ribe, Ute Indian T ribe, and Ute Mountain Ute T ribe. 63 U.S. Bureau of Reclamation, Colorado River T en T ribes Partnership, U.S. Bureau of Reclamation, Colorado River T en T ribes 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. Study Report, December 2018, p. 5.11 -1, at https://www.usbr.gov/lc/region/programs/crbstudy/tws/finalreport.html.
Hereinafter “T en Tribes Study, 2018.” Hereinafter “T en Tribes Study, 2018.”
5964 T en T ribes Study, 2018, pp. 5.11-1-5.11-2. T en T ribes Study, 2018, pp. 5.11-1-5.11-2.
6065 T en T ribes Study, 2018, p. 5.11-4. T en T ribes Study, 2018, p. 5.11-4.
6166 National Research Council, Committee on the Scientific Bases of Colorado River Basin National Research Council, Committee on the Scientific Bases of Colorado River Basin ~~Water~~Wat er Management, Water Science Management, Water Science
and T echnology Board, and T echnology Board, Colorado River Basin Water Managem ent: Evaluating and Adjusting to Hydroclim atic Variability, 2007, , 2007,
at https://www.nap.edu/read/11857/chapter/1. at https://www.nap.edu/read/11857/chapter/1.
62 67 For dataset on natural flows and more information, see Bureau of Reclamation, Lower Colorado River Operations, “General For dataset on natural flows and more information, see Bureau of Reclamation, Lower Colorado River Operations, “General
Modeling Information,” at https://www.usbr.gov/lc/region/g4000/riverops/model-info.html. Modeling Information,” at https://www.usbr.gov/lc/region/g4000/riverops/model-info.html.
6368 Bureau of Reclamation Flow Data, 1906-2018. Bureau of Reclamation Flow Data, 1906-2018.
6469 “Consumptive Uses and Losses” includes reservoir evaporation and other consumptive use losses, which average in excess of 2 “Consumptive Uses and Losses” includes reservoir evaporation and other consumptive use losses, which average in excess of 2
~~MAF per year.~~
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13 MAF to over 16 MAF annual y. 13 MAF to over 16 MAF annual y.6570 These levels dropped after the 2003 approval of the Quantitative These levels dropped after the 2003 approval of the Quantitative
Settlement Agreement (QSA) (see below section, Settlement Agreement (QSA) (see below section, “Recent Developments and Agreements”) and have ) and have
ranged from 14-15.5 MAF since that time, in part due to decreasing consumptive use in the Lower ranged from 14-15.5 MAF since that time, in part due to decreasing consumptive use in the Lower
Basin.Basin.6671 The combined trends in natural flows and consumptive use/losses have caused a significant The combined trends in natural flows and consumptive use/losses have caused a significant
drawdown of basin storage levels drawdown of basin storage levels.
~~The current drought in the basin has included some of the lowest flows on record.67~~ (Figure 4). Figure 4. Combined Storage: Lake Powell and Lake Mead, 1999-2020 (percentage of total storage) Source: Congressional Research Service, based on data in Bureau of Reclamation Annual Operating Plans for Colorado River Reservoirs. Note: Total storage = 52.3 mil ion acre-feet. MAF per year. 70 1971-2008 consumptive use data based on data in Reclamation 2012 Supply/Demand Study, Technical Report C, p. C-6. Analysis of 2009-2015 Upper Basin consumptive use data by CRS, based on data in Provisional Bureau of Reclamation Consumptive Uses and Losses Reports for 2006 -2010, 2011-2015, and 2016-2020. Analysis of 2009-2015 Lower Basin consumptive use data by CRS, based on Bureau of Reclamation Colorado River Water Accounting and Use Reports for 2009 -2015. Hereinafter, references to consumptive use data analysis based on these four r eports are referred to collectively as “ CRS Analysis of Colorado River Consumptive Use Data.” 71 Consumptive use in the Lower Basin has decreased from totals in excess of 8.41 MAF in 2002 to a low of 6.56 MAF in 2019. CRS Analysis of Colorado River Consumptive Use Data. Congressional Research Service 16 Management of the Colorado River: Water Allocations, Drought, and the Federal Role The current drought in the basin has included some of the lowest flows on record.72 Observers have Observers have
pointed out that flows in some recent years have been lower than would be expected given the amount of pointed out that flows in some recent years have been lower than would be expected given the amount of
precipitation that has occurred, and have noted that warmer temperatures appear to be a significant precipitation that has occurred, and have noted that warmer temperatures appear to be a significant
contributor to these diminished flows.contributor to these diminished flows.6873 Based on these and other observations, some have argued that Based on these and other observations, some have argued that
Colorado River flows are unlikely to return to 20th century averages, and that future water supply risk is Colorado River flows are unlikely to return to 20th century averages, and that future water supply risk is
high. high.6974
A 2012 study by Reclamation projected a long-term imbalance in supply and demand in the Colorado A 2012 study by Reclamation projected a long-term imbalance in supply and demand in the Colorado
River Basin.River Basin.7075 In the study, Reclamation noted that the basin had thus far avoided serious impacts on 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 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 al ocations.Basin states have yet to fully develop the use of their al ocations.7176 However, Reclamation projected that However, Reclamation projected that
in the coming half century, flows would decrease by an average of 9% at Lee Ferry and drought would in the coming half century, flows would decrease by an average of 9% at Lee Ferry and drought would
increase in frequency and duration.increase in frequency and duration.7277 At the same time, Reclamation projected that demand for basin At the same time, Reclamation projected that demand for basin
water supplies would increase, with annual consumptive use projected to rise from 15 MAF to 18.1-20.4 water supplies would increase, with annual consumptive use projected to rise from 15 MAF to 18.1-20.4
MAF by 2050, depending on population growth.MAF by 2050, depending on population growth.7378 A range of 64%-76% of the growth in demand was A range of 64%-76% of the growth in demand was
expected to come from increased M&I demand. expected to come from increased M&I demand.7479
Reclamation’s 2012 study also posited several potential ways to al eviate future shortages in the basin, Reclamation’s 2012 study also posited several potential ways to al eviate future shortages in the basin,
such as alternative water supplies, demand management, drought action plans, water banking, and water such as alternative water supplies, demand management, drought action plans, water banking, and water
transfer/markets. Some of these options already are being pursued. In particular, some states have become transfer/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 increasingly active in banking unused Colorado River surface water supplies, including through
groundwater banks or storage of unused surface waters in Lake Mead. groundwater banks or storage of unused surface waters in Lake Mead.

~~65 1971-2008 consumptive use data based on data in Reclamation 2012 Supply/Demand Study , Technical Report C, p. C-6.~~
~~Analysis of 2009-2015 Upper Basin consumptive use data by CRS, based on data in Provisional Bureau of Reclamation~~
~~Consumptive Uses and Losses Reports for 2006 -2010, 2011-2015, and 2016-2020. Analysis of 2009-2015 Lower Basin~~
~~consumptive use data by CRS, based on Bureau of Reclamation Colorado River Water Accounting and Use Reports for 2009 -~~
~~2015. Hereinafter, references to consumptive use data analysis based on these four reports are referred to collectively as “CRS~~
~~Analysis of Colorado River Consumptive Use Data.”~~
~~66 Consumptive use in the Lower Basin has decreased from totals in excess of 8.41 MAF in 2002 to a low of 6.56 MAF in 2019.~~
~~CRS Analysis of Colorado River Consumptive Use Data.~~
67 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.80 Drought and other uncertainties related to water rights priorities (e.g., potential tribal water rights claims) spurred the development of several efforts that general y attempted to relieve pressure on basin water supplies, stabilize storage levels, and provide assurances of 72 T he 2000-2018 period included the second, third, fourth, and fifth lowest years on record. T he 2000-2018 period included the second, third, fourth, and fifth lowest years on record.
6873 Woodhouse, C.A., G.T . Pederson, and K. Horino, et al., “Increasing influence of air temperature on upper Colorado River Woodhouse, C.A., G.T . Pederson, and K. Horino, et al., “Increasing influence of air temperature on upper Colorado River
streamflow,” streamflow,” Geophysical Research Letters, vol. 43 (2016), pp. 2174-2181. , vol. 43 (2016), pp. 2174-2181.
6974 Udall, B. and J. Overpeck, “T he twenty-first century Colorado River hot drought and implications for the future,” Udall, B. and J. Overpeck, “T he twenty-first century Colorado River hot drought and implications for the future,” Water
Resources Research, vol. 53 (February 17, 2017), pp. 2404 -2418. , vol. 53 (February 17, 2017), pp. 2404 -2418.
7075 Reclamation 2012 Supply/Demand Study. Reclamation 2012 Supply/Demand Study.
7176 T his is largely due to a lack of development in Wyoming (which uses approximately 500,000 acre -feet of its 1 MAF in T his 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). Colorado River supplies) and Utah (which uses approximately 800,000 acre -feet of its 1.7 MAF in supplies).
72 77 Reclamation 2012 Supply/Demand Study, p. 7. Reclamation 2012 Supply/Demand Study, p. 7.
7378 Reclamation 2012 Supply/Demand Study, p. 8. Population growth in central Arizona and on the Reclamation 2012 Supply/Demand Study, p. 8. Population growth in central Arizona and on the ~~Fr ont~~Front Range of Colorado is Range of Colorado is
expected to comprise the majority of basin population increases. expected to comprise the majority of basin population increases.
7479 Reclamation 2012 Supply/Demand Reclamation 2012 Supply/Demand ~~Study~~St udy, , Technical Report C, p. C-22. T he majority of this demand increase was assumed to , p. C-22. T he majority of this demand increase was assumed to
come from Central Arizona and the Front Range in Colorado. come from Central Arizona and the Front Range in Colorado.
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~~Management of the Colorado River: Water Allocations, Drought, and the Federal Role~~

~~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.75 Drought and other uncertainties related to water rights priorities~~
~~(e.g., potential tribal water rights claims) spurred the development of several efforts that general y~~
~~attempted to relieve pressure on basin water supplies, stabilize storage levels, and provide assurances of~~
80 A compact call 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 Castle, Anne and Fleck, John, “ T he Risk of Curtailment under the Colorado River Compact,” November 8, 2019, https://ssrn.com/abstract=3483654. Congressional Research Service 17 Management of the Colorado River: Water Allocations, Drought, and the Federal Role available water supplies. Some of the most prominent developments since the year 2000 (i.e., the available water supplies. Some of the most prominent developments since the year 2000 (i.e., the
beginning of the current drought) are discussed below. 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,
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.7681 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 Al -American Canal); and providing for several large-scale, long-water supplies (e.g., the lining of the Al -American Canal); and providing for several large-scale, long-
term agriculture-to-urban water transfers. The QSA also committed the state to a path for restoration and term agriculture-to-urban water transfers. The QSA also committed the state to a path for restoration and
mitigation related to the Salton Sea, a water body in Southern California that was historical y sustained by mitigation related to the Salton Sea, a water body in Southern California that was historical y sustained by
Colorado River irrigation runoff from the Imperial and Coachel a Val eys. Colorado River irrigation runoff from the Imperial and Coachel a Val eys.7782
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 2004.7883 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.7984
2004 Arizona Water Settlements Act
The 2004 Arizona Water Settlements Act (P.L. 108-451, AWSA) significantly altered the al ocation of The 2004 Arizona Water Settlements Act (P.L. 108-451, AWSA) significantly altered the al ocation of
~~CAP water in Arizona and set the stage for some of the cutbacks in the state that are currently under~~
~~discussion.80~~CAP water in Arizona.85 It ratified three water rights settlements (one in each title) between the federal government 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 and the State of Arizona, the Gila River Indian Community (GRIC), and the Tohono O’odham Nation, respectively.86 For the state and its CAP water users, the set lement resolved a final repayment cost for CAP by reducing the water users’ reimbursable repayment obligation from about $2.3 bil ion to $1.65 bil ion. Additional y, Arizona agreed to new tribal and non-tribal al ocations of CAP water so that approximately half of CAP’s annual al otment 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. 81~~O’odham Nation,~~

~~75 A compact call 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 Castle, Anne and Fleck, John, “ T he Risk of Curtailment under the~~
~~Colorado River Compact,” November 8, 2019, https://ssrn.com/abstract=3483654.~~
76 California Quantification Settlement Agreement by and Among Imperial Irrigation District, the Metropolitan Water District of California Quantification Settlement Agreement by and Among Imperial Irrigation District, the Metropolitan Water District of
Southern California, and Coachella Valley Water District, October 10, 2003. Southern California, and Coachella Valley Water District, October 10, 2003.
7782 For more information on the Salton Sea, see CRS In Focus IF11104, For more information on the Salton Sea, see CRS In Focus IF11104, Salton Sea Management and Restoration Efforts, by , by
Pervaze A. Sheikh and Charles V. Stern. Pervaze A. Sheikh and Charles V. Stern.
78 83 Bureau of Reclamation, Bureau of Reclamation, Record of Decision for the Colorado River Water Delivery Agreement, October 10, 2003, pp 16-19. , October 10, 2003, pp 16-19.
Hereinafter Reclamation, Hereinafter Reclamation, Colorado River Water Delivery Agreem ent.
7984 Reclamation, Reclamation, Colorado River Water Delivery Agreement. .
8085 P.L. 108-451. 86 Congress passed the CRBPA and authorized construction of CAP despite significant uncertainty related to tribal water rights related to the Colorado River. T he 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 adjacent to Phoenix. Additionally, the T ohono O’odham Nation possessed reserved water rights near T ucson with the potential to disrupt that city’s water supplies. Congressional Research Service 18 link to page 28 link to page 25 link to page 26 Management of the Colorado River: Water Allocations, Drought, and the Federal Role ~~P.L. 108-451.~~
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~~respectively.81 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 bil ion to $1.65~~
~~bil ion. Additional y, Arizona agreed to new tribal and non-tribal al ocations of CAP water so that~~
~~approximately half of CAP’s annual al otment 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 also 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.~~
2007 Interim Guidelines/Coordinated Operations for Lake Powell and
Lake Mead
Another significant development in the basin was the 2007 adoption of the Colorado River Interim Another significant development in the basin was the 2007 adoption of the Colorado River Interim
Guidelines for Lower Basin Shortages and the Coordinated Operations for Lake Powel and Lake Mead Guidelines for Lower Basin Shortages and the Coordinated Operations for Lake Powel and Lake Mead
(2007 Interim Guidelines). Development of the agreement began in 2005, when, in response to drought in (2007 Interim Guidelines). Development of the agreement began in 2005, when, in response to drought in
the Southwest and the decline in basin water storage (and a record low point in Lake Powel of 33% the Southwest and the decline in basin water storage (and a record low point in Lake Powel of 33%
active capacity), the Secretary of the Interior instructed Reclamation to develop coordinated strategies for active capacity), the Secretary of the Interior instructed Reclamation to develop coordinated strategies for
Colorado River reservoir operations during drought or shortages.Colorado River reservoir operations during drought or shortages.8287 The resulting guidelines included The resulting guidelines included
criteria for releases from Lakes Mead and Powel determined by “trigger levels” in both reservoirs, as criteria for releases from Lakes Mead and Powel determined by “trigger levels” in both reservoirs, as
wel as a schedule of Lower Basin curtailments at different operational tiers wel as a schedule of Lower Basin curtailments at different operational tiers (Table 2). Under the . Under the
guidelines, Arizona and Nevada, which have junior rights to California, would face reduced al ocations if guidelines, Arizona and Nevada, which have junior rights to California, would face reduced al ocations if
Lake Mead elevations dropped below 1,075 ft. At the time, it was thought that the 2007 Guidelines would Lake Mead elevations dropped below 1,075 ft. At the time, it was thought that the 2007 Guidelines would
significantly reduce the risk of Lake Mead fal ing to 1,025 ft. significantly reduce the risk of Lake Mead fal ing to 1,025 ft.
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 Intentional y Created Surplus (ICS). were able to store conserved water in Lake Mead, known as Intentional y Created Surplus (ICS).
Reclamation accounts for this water annual y, and the users storing the water may access the surplus in Reclamation accounts for this water annual y, and the users storing the water may access the surplus in
future years, in accordance with the Law of the River. As of 2019, the portion of Lake Mead water in future years, in accordance with the Law of the River. As of 2019, the portion of Lake Mead water in
storage that was classified as ICS reached a new high of 2.312 MAF storage that was classified as ICS reached a new high of 2.312 MAF (Figure 4~~).83~~5).88
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, beginning in 2020, Reclamation end of 2026). Thus, beginning in 2020, Reclamation ~~is coordinating “reconsultation” on~~coordinated a review on the effectiveness of the 2007 the 2007
guidelines. guidelines. ~~These~~Forthcoming reconsultation reconsultation ~~efforts are to also~~ on the 2007 guidelines also wil encompass negotiations related to renewal of the encompass negotiations related to renewal of the
Upper and Lower Basin Drought Contingency Plans, which are an overlay on the 2007 Upper and Lower Basin Drought Contingency Plans, which are an overlay on the 2007 guidelines (see guidelines (see
below section, below section, “2019 Drought Contingency Plans””). 87).

~~81 Congress passed the CRBPA and authorized construction of CAP despite significant uncertainty related to tribal water rights~~
~~related to the Colorado River. T he 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 adjacent to Phoenix. Additionally, the~~
~~T ohono O’odham Nation possessed reserved water rights near T ucson with the potential to disrupt that city’s water supplies.~~
82 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.)
8388 Bureau of Reclamation, Bureau of Reclamation, Colorado River Accounting and Water Use Report, Calendar Year 2019, 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 45. U.S. Lower Basin States: Intentionally Created Surplus Balance, 2010-2019

Source: Figure by CRS, based on data from Bureau of Reclamation, Figure by CRS, based on data from Bureau of Reclamation, Colorado River Accounting and Water Use Report,
Calendar Years 2010-2019, at https://www.usbr.gov/lc/region/g4000/wtracct.html. , at https://www.usbr.gov/lc/region/g4000/wtracct.html.
Pilot 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. These activities had the goal of developing voluntary conservation projects and reductions of water use. These activities had the goal of developing
new new system water,,8489 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 2019.8590 Congress formal y Congress formal y
authorized federal participation in these efforts in the Energy and Water Development and Related 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 Agencies Appropriations Act, 2015 (P.L. 113-235, Division D), with an initial sunset date for the authority

8489 System water refers to water that is provided to increase water supplies as a whole, without being directed toward additional 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. consumptive use for specific contractors or water users.
8590 Agreement Among the United States of America, T hrough the Department of the Interior, Bureau of Reclamation, the Central Agreement Among the United States of America, T hrough 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 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 T hrough Voluntary Nevada Water Authority, for a Pilot Program for Funding the Creation of Colorado River System Water T hrough Voluntary
Water Conservation and Reductions in Use, Agreement No. 14-XX-30-W0574, July 30, 2014, at https://www.usbr.gov/lc/region/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. programs/PilotSysConsProg/PilotSCPFundingAgreement7-30-2014.pdf.
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at the end of FY2018. at the end of FY2018.8691 The Energy and Water Development and Related Agencies Appropriations Act, The Energy and Water Development and Related Agencies Appropriations Act,
2019 (P.L. 115-244, Division A) extended the authority through the end of FY2022, with the stipulation 2019 (P.L. 115-244, Division A) extended the authority through the end of FY2022, with the stipulation
that Upper Basin agreements could not proceed without the participation of the Upper Basin states 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.8792 As of September 2019, Reclamation estimated that the As of September 2019, Reclamation estimated that the
Lower Basin program had resulted in a total of 175,347 AF of system water conserved, at an average cost Lower Basin program had resulted in a total of 175,347 AF of system water conserved, at an average cost
of $170.14 per AF.of $170.14 per AF.8893 Additional projects Additional projects ~~were also being~~also were carried out in the Upper Basin by the Upper carried out in the Upper Basin by the Upper
Colorado Colorado River Basin CommissionRiver Basin Commission~~.89~~, but these efforts ended in 2018.94
Minute 319 and Minute 323 Agreements with ~~Mexico90~~Mexico95
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 agreementprevious agreement related to implementation of the 1944 U.S.-Mexico Water Treaty, Minute 319, signed in 2012., Minute 319, signed in 2012.9196 Minute 323 Minute 323 ~~included~~includes, among other things, options for , among other things, options for
Mexico to hold water in reserve in U.S. reservoirs for emergencies and water conservation efforts, as wel Mexico to hold water in reserve in U.S. reservoirs for emergencies and water conservation efforts, as wel
as U.S. commitments for flows to support the ecological health of the Colorado River Delta. It also as U.S. commitments for flows to support the ecological health of the Colorado River Delta. It also
extended initial Mexican cutback extended initial Mexican cutback commitments made under Minute 319 (which were similar in structure 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 to the 2007 cutbacks negotiated for Lower Basin states) and established a Binational Water Scarcity
Contingency Plan that included Contingency Plan that included ~~additional~~ additional cutbacks that would be triggered if drought contingency plans cutbacks that would be triggered if drought contingency plans
(DCPs) are approved by U.S. (DCPs) are approved by U.S. basin states (see following section, basin states (see following section, “2019 Drought Contingency Plans”). ”).
2019 Drought Contingency Plans
Ongoing drought conditions and the potential for water supply shortages prompted discussions and Ongoing drought conditions and the potential for water supply shortages prompted discussions and
negotiations focused on how to conserve additional basin water supplies. After several years of negotiations focused on how to conserve additional basin water supplies. After several years of
negotiations, on March 19, 2019, Reclamation and the Colorado River Basin states finalized DCPs for negotiations, on March 19, 2019, Reclamation and the Colorado River Basin states finalized DCPs for
both the Upper Basin and the Lower Basin. These plans required final authorization by Congress to be 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 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 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 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. 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 Powel reaching critical y low elevations through The Upper Basin DCP aims to protect against Lake Powel reaching critical y low elevations through
coordinated Upper Basin reservoir operations; it also authorizes storage of conserved water in the Upper 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 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.Program”) that may be developed in the future.9297 Under the Upper Basin DCP, the Upper Basin states Under the Upper Basin DCP, the Upper Basin states
agree to operate system units to keep the surface of Lake Powel above 3,525 ft, which is 35 ft above the agree to operate system units to keep the surface of Lake Powel above 3,525 ft, which is 35 ft above the
~~minimum elevation needed to run the dam’s hydroelectric plant. Other large Upper Basin reservoirs (e.g.,~~

8691 P.L. 113-235, §206. P.L. 113-235, §206.
8792 P.L. 115-244, §205. P.L. 115-244, §205.
88 93 Lower Colorado Region,Lower Colorado Region, “Pilot System Conservation Program,” at https://www.usbr.gov/lc/region/programs/“Pilot System Conservation Program,” at https://www.usbr.gov/lc/region/programs/
PilotSysConsProg/pilotsystem.html. Accessed September 24, 2020. PilotSysConsProg/pilotsystem.html. Accessed September 24, 2020.
8994 For more information, see http://www.ucrcommission.com/system-conservation-pilot-program/. For more information, see http://www.ucrcommission.com/system-conservation-pilot-program/.
9095 For more information on the 1994 U.S.-Mexico Water T reaty and Colorado River water sharing issues with Mexico, see CRS For more information on the 1994 U.S.-Mexico Water T reaty 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.
9196 T he text of these minutes is available from the International Boundary and Water Commission at https://www.ibwc.gov/ T he text of these minutes is available from the International Boundary and Water Commission at https://www.ibwc.gov/
T reaties_Minutes/Minutes.html. T reaties_Minutes/Minutes.html.
9297 While such a mechanism exists for the Lower Basin, a comparable program has yet to be developed in the Upper Basin. While such a mechanism exists for the Lower Basin, a comparable program has yet to be developed in the Upper Basin.
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link to page link to page 2628 link to page link to page 2628 Management of the Colorado River: Water Allocations, Drought, and the Federal Role

minimum elevation needed to run the dam’s hydroelectric plant. Other large Upper Basin reservoirs (e.g., Navajo Reservoir, Blue Mesa Reservoir, and Flaming Gorge Reservoir) would be operated to protect the Navajo Reservoir, Blue Mesa Reservoir, and Flaming Gorge Reservoir) would be operated to protect the
targeted Lake Powel elevation, potential y through drawdown of their own storage. If established by the targeted Lake Powel elevation, potential y through drawdown of their own storage. If established by the
states, an Upper Basin DCP Demand Management Program would likely entail wil ing sel er/buyer states, an Upper Basin DCP Demand Management Program would likely entail wil ing sel er/buyer
agreements al owing for temporary paid reductions in water use that would provide for more storage agreements al owing for temporary paid reductions in water use that would provide for more storage
volume in Lake Powel . volume in Lake Powel .
Reclamation and other observers have stated their belief that these efforts wil Reclamation and other observers have stated their belief that these efforts wil ~~sdecrease~~decrease the risk of Lake the risk of Lake
Powel ’s elevation fal ing below 3,490 ft, an elevation at which Powel ’s elevation fal ing below 3,490 ft, an elevation at which ~~significantly reduced~~a significant reduction in hydropower hydropower
generation generation ~~is possible.93~~would occur.98
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 ft under the 2007 Interim Guidelines) have committed to have their supplies curtailed beginning at 1,075 ft under the 2007 Interim Guidelines) have committed to
contributing additional supplies to maintain higher lake levels (i.e., beyond previous commitments). contributing additional supplies to maintain higher lake levels (i.e., beyond previous commitments).
These reductions begin at 1,090 ft and would reach their maximums when reservoir levels drop below These reductions begin at 1,090 ft and would reach their maximums when reservoir levels drop below
1,045 ft. At the same time, the Lower Basin DCP includes—for the first time—delivery cutbacks for 1,045 ft. At the same time, the Lower Basin DCP includes—for the first time—delivery cutbacks for
California. These curtailments begin with a 200,000 AF delivery reduction at Lake Mead elevations of California. These curtailments begin with a 200,000 AF delivery reduction at Lake Mead elevations of
1,040-1,045 ft and would increase by 50,000 AF for each additional 5 foot drop in Lake Mead elevation, 1,040-1,045 ft and would increase by 50,000 AF for each additional 5 foot drop in Lake Mead elevation,
to as much as 350,000 AF at elevations of 1,025 ft or lower. to as much as 350,000 AF at elevations of 1,025 ft 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 iGuidelines and under Minute 323 with Mexico. Specific and cumulative reductions are shown in Table 2.
In addition to the state-level reductions, under the Lower Basin DCP, Reclamation also agreed to pursue In addition to the state-level reductions, under the Lower Basin DCP, Reclamation also agreed to pursue
efforts to add 100,000 AF or more of “system water” within the basin. Some of the largest and most efforts to add 100,000 AF or more of “system water” within the basin. Some of the largest and most
controversial reductions under the Lower Basin DCP were committed to by Arizona, where pursuant to controversial reductions under the Lower Basin DCP were committed to by Arizona, where pursuant to
previous changes under the 2004 AWSA, a large group of agricultural users face major cutbacks to their previous changes under the 2004 AWSA, a large group of agricultural users face major cutbacks to their
CAP water supplies. The Tier Zero Arizona curtailment of 192,000 AF at Tier Zero represents a 12% CAP water supplies. The Tier Zero Arizona curtailment of 192,000 AF at Tier Zero represents a 12%
reduction in CAP water supplies. reduction in CAP water supplies.
Reclamation has noted that the Lower Basin DCP significantly decreases the chance of Lake Mead Reclamation has noted that the Lower Basin DCP significantly decreases the chance of Lake Mead
elevations fal ing below 1,020 ft, which would be a critical y low level.elevations fal ing below 1,020 ft, which would be a critical y low level.9499 Some parties have pointed out Some parties have pointed out
that although the DCP is unlikely to prevent a shortage from being declared at 1,075 ft, it would slow the that although the DCP is unlikely to prevent a shortage from being declared at 1,075 ft, it would slow the
rate at which the lake recedes thereafter.rate at which the lake recedes thereafter.95100 Combined with the commitments from Mexico, total planned Combined with the commitments from Mexico, total planned
cutbacks under shortage scenarios (i.e., al commitments to date, combined) would reduce Lower cutbacks under shortage scenarios (i.e., al commitments to date, combined) would reduce Lower ~~Basin~~Bas in
consumptive use by 241,000 AF to 1.375 MAF per year, depending on the curtailments triggered by Lake consumptive use by 241,000 AF to 1.375 MAF per year, depending on the curtailments triggered by Lake
Mead’s elevation. Mead’s elevation.96101

9398 Bureau of Reclamation, “Presentation to Congressional Staff on Draft Drought Contingency Plans,” October 16, Bureau of Reclamation, “Presentation to Congressional Staff on Draft Drought Contingency Plans,” October 16, ~~20 18~~2018. .
Hereinafter “2018 Reclamation DCP Presentation.” Hereinafter “2018 Reclamation DCP Presentation.”
9499 2018 Reclamation DCP Presentation. Currently, there are no agreed-upon curtailment levels governing operations below 1,020 2018 Reclamation DCP Presentation. Currently, there are no agreed-upon curtailment levels governing operations below 1,020
ft, thus that level represents an unknown and likely more severe level of ft, thus that level represents an unknown and likely more severe level of ~~curt ailment~~curtailment that would affect more users than those that would affect more users than those
affected under the 2007 guidelines. affected under the 2007 guidelines.
95100 T om Buschatzke, Arizona Department of Water Resources Director, and T ed Cooke, Central Arizona Project General T om Buschatzke, Arizona Department of Water Resources Director, and T ed Cooke, Central Arizona Project General
Manager, “ T he DCP Makes CO River Delivery Shortfalls Less Painful, but It Doesn’t Make T hem Go Away,” Arizona Manager, “ T he DCP Makes CO River Delivery Shortfalls Less Painful, but It Doesn’t Make T hem Go Away,” Arizona
Department of Water Resources, September 5, 2018, at https://new.azwater.gov/news/articles/2018-05-09. Department of Water Resources, September 5, 2018, at https://new.azwater.gov/news/articles/2018-05-09.
96101 For a summary of the For a summary of the ~~curtailment s~~curtailments that add up to this amount, see “1,090 that add up to this amount, see “1,090 ->1,075” row o->1,075” row of Table 2.
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Table 2. Lower Basin Water Delivery Curtailment Volumes Under Existing Agreements
values in thousands of acre-feet values in thousands of acre-feet
Binational
Minute 323
Water
2007 Interim
Delivery
Scarcity
Total Volume of Curtailment
Shortage Guidelines
Reductions
DCP Curtailment
Conting. Plan
(% of Colorado River Apportionment)
Lake Mead
Elevation
Lower
(ft)
AZ
NV
Mexico
AZ
NV
CA
Mexico
AZ
NV
CA
Basin
Mexico
1,090 - 1,090 -
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 - 1,075 -
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 - 1,050 -
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 - 1,045 -
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 - 1,040 -
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 - 1,035 -
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 - 1,030 -
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 <1,025
480 480
20 20
125 125
240 240
10 10
350 350
150 150
720 (22.8%) 30 (10.0%) 720 (22.8%) 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, the Minute 323 between Mexico and the United States, the Lower Basin Drought Contingency Plan, ,
and the Binational Water Scarcity Contingency Plan in Minute 323 between Mexico and the United States. and 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

Opposition
Although the DCPs and the related negotiations were widely praised, some expressed concerns Although the DCPs and the related negotiations were widely praised, some expressed concerns
related to the implementation of the DCPs as they relate to federal and state environmental laws. related to the implementation of the DCPs as they relate to federal and state environmental laws.
Most Colorado River contractors supported the agreements, but one major basin contractor, Most Colorado River contractors supported the agreements, but one major basin contractor,
Imperial Irrigation District (IID, a major holder of Colorado River water rights in Southern Imperial Irrigation District (IID, a major holder of Colorado River water rights in Southern
California), did not approve the DCPs. IID has argued that the DCPs wil further degrade the California), did not approve the DCPs. IID has argued that the DCPs wil further degrade the
Salton Sea, a shrinking and ecological y degraded water body in southern California that relies on Salton Sea, a shrinking and ecological y degraded water body in southern California that relies on
drainage flows from lands irrigated using Colorado River water. IID made support for the drainage flows from lands irrigated using Colorado River water. IID made support for the
agreements contingent on corresponding federal support for Salton Sea restoration efforts. agreements contingent on corresponding federal support for Salton Sea restoration efforts.97102
While other basin interests have general y agreed with the need to mitigate and restore parts of While other basin interests have general y agreed with the need to mitigate and restore parts of
the Salton Sea, some have disagreed with IID’s linking of the Salton Sea to the DCPs.the Salton Sea, some have disagreed with IID’s linking of the Salton Sea to the DCPs.98103
Following enactment of the DCPs, IID filed suit in state court al eging that state approval of the Following enactment of the DCPs, IID filed suit in state court al eging that state approval of the
DCPs violated the California Environmental Quality Act. DCPs violated the California Environmental Quality Act.99104
Issues for Congress
Funding and Oversight of Existing Facilities and Programs
The principal role of Congress as it relates to storage facilities on the Colorado River is funding The principal role of Congress as it relates to storage facilities on the Colorado River is funding
and oversight of facility operations, construction, and programs to protect and restore endangered 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 species (e.g., Glen Canyon Dam Adaptive Management Program and the Upper Colorado River
Endangered Fish Program). In the Upper Basin, Colorado River facilities include the 17 active Endangered Fish Program). In the Upper Basin, Colorado River facilities include the 17 active
participating units in the Colorado River Storage Projects, as wel as the Navajo-Gal up Water participating units in the Colorado River Storage Projects, as wel as the Navajo-Gal up 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 Al -American Canal, Yuma and Gila Projects, Parker-Davis Roosevelt Dam, Hoover Dam and Al -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 typical y Congressional appropriations in support of Colorado River projects and programs typical y
account for a portion of overal project budgets. For example, for the most recent year available account for a portion of overal project budgets. For example, for the most recent year available
(FY2018), the Lower Colorado Region’s (FY2018), the Lower Colorado Region’s operating budget was $559.5 mil ion; $134.8 mil ion of operating budget was $559.5 mil ion; $134.8 mil ion of
this total was provided by discretionary appropriations, and the remainder of funding came from this total was provided by discretionary appropriations, and the remainder of funding came from
power revenues (which are made available without further appropriation) and nonfederal power revenues (which are made available without further appropriation) and nonfederal
partners.partners.~~100~~105 In recent years, Congress has also authorized and appropriated funding that has In recent years, Congress has also authorized and appropriated funding that has

97102 IID, the largest water rights holder on the Colorado River, did not approve the Lower Basin DCP. While there were IID, the largest water rights holder on the Colorado River, did not approve the Lower Basin DCP. While there were
no formal requirements for IID delivery curtailments under the Lower Basinno formal requirements for IID delivery curtailments under the Lower Basin DCP (other contractors have committed to DCP (other contractors have committed to
implementing California’s curtailments), IID objected to the lack of commitments for Salton Sea restoration implementing California’s curtailments), IID objected to the lack of commitments for Salton Sea restoration ~~un der~~under the the
plans. For more information, see CRS In Focus IF11104, plans. For more information, see CRS In Focus IF11104, Salton Sea Management and Restoration Efforts, by Pervaze , by Pervaze
A. Sheikh and Charles V. Stern. A. Sheikh and Charles V. Stern.
98103 See, for example, T om Buschatzke, et al., “Colorado River Drought Contingency Plan Is Necessary Now,” See, for example, T om Buschatzke, et al., “Colorado River Drought Contingency Plan Is Necessary Now,” The
Desert Sun, March 28, 2019, at https://www.desertsun.com/story/opinion/contributors/valley-voice/2019/03/26/, March 28, 2019, at https://www.desertsun.com/story/opinion/contributors/valley-voice/2019/03/26/
colorado-river-drought -contingency-plan-necessary-dcp/3272667002/. colorado-river-drought -contingency-plan-necessary-dcp/3272667002/.
99104 IID, “Salton Sea Is Focus of IID’s Legal Challenge to Drought Contingency Plan,” press release, April 17, 2019, IID, “Salton Sea Is Focus of IID’s Legal Challenge to Drought Contingency Plan,” press release, April 17, 2019,
https://www.iid.com/Home/Components/News/News/685/30?backlist=%2f. https://www.iid.com/Home/Components/News/News/685/30?backlist=%2f.
~~100~~105 Bureau of Reclamation, Bureau of Reclamation, Lower Colorado Region Annual Report, FY2018, at https://www.usbr.gov/lc/docs/, at https://www.usbr.gov/lc/docs/
LCRegionReportFY18.pdf. LCRegionReportFY18.pdf.
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targeted the Colorado River Basin in general (i.e., the Pilot System Conservation Plan). Congress targeted the Colorado River Basin in general (i.e., the Pilot System Conservation Plan). Congress
may choose to extend or amend these and other authorities specific to the basin. may choose to extend or amend these and other authorities specific to the basin.
While discretionary appropriations for the Colorado River are of regular interest to Congress, While discretionary appropriations for the Colorado River are of regular interest to Congress,
Congress may also be asked to weigh in on Colorado River funding that is not subject to regular Congress may also be asked to weigh in on Colorado River funding that is not subject to regular
appropriations. For instance, in the coming years, the Lower Colorado River Basin Development appropriations. For instance, in the coming years, the Lower Colorado River Basin Development
Fund is projected to face a decrease in Fund is projected to face a decrease in ~~revenues101~~revenues106 and may thus have less funding available for and may thus have less funding available for
congressional y established funding priorities for the Development Fund. congressional y established funding priorities for the Development Fund.
Indian Water Rights Settlements
Congress has previously approved Indian water rights settlements associated with more than Congress has previously approved Indian water rights settlements associated with more than
2 MAF of tribal diversion rights on the Colorado River. Only a portion of this water has been 2 MAF of tribal diversion rights on the Colorado River. Only a portion of this water has been
developed. Congress likely wil face ongoing decisions regarding whether to fund development of developed. Congress likely wil face ongoing decisions regarding whether to fund development of
previously authorized infrastructure associated with Indian water rights settlements in the previously authorized infrastructure associated with Indian water rights settlements in the
Colorado River Basin. For example, the Navajo-Gal up Water Supply Project is being built to Colorado River Basin. For example, the Navajo-Gal up Water Supply Project is being built to
serve the Jicaril a Apache Nation, the Navajo Nation, and the City of Gal up, New Mexico.serve the Jicaril a Apache Nation, the Navajo Nation, and the City of Gal up, New Mexico.~~102~~107
Congress may also be asked to consider new settlements that may result in tribal rights to more Congress may also be asked to consider new settlements that may result in tribal rights to more
Colorado River water. For example, in the 116th Congress, H.R. Colorado River water. For example, in the 116th Congress, H.R. ~~244~~644 would authorize the Navajo would authorize the Navajo
Nation Water Settlement in Utah. Nation Water Settlement in Utah.
Plans for New and Augmented Water Storage, Conveyance
~~In addition to development of new tribal water supplies, some~~Some states in the Upper Basin have states in the Upper Basin have
indicated their intent to further develop their Colorado River water entitlements. For example, in indicated their intent to further develop their Colorado River water entitlements. For example, in
the 115th Congress, Section 4310 of America’s Water Infrastructure Act (P.L. 115-270) authorized 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 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 state would fund a project to add erosion control to Fontenel e Reservoir in the Upper Basin. The control to Fontenel e Reservoir in the Upper Basin. The
project would al ow the state to potential y utilizeproject would al ow the state to potential y utilize an additionalan additional 80,000 acre-feet of water storage 80,000 acre-feet of water storage
on the Green River, a tributary on the Green River, a tributary of the Colorado River. of the Colorado River.
Another project that would develop Upper Basin waters is the proposed Lake Powel Pipeline Another project that would develop Upper Basin waters is the proposed Lake Powel Pipeline
(LPP), which would direct approximately 86,000 acre-feet of Utah’s Upper Basin Colorado River (LPP), which would direct approximately 86,000 acre-feet of Utah’s Upper Basin Colorado River
Basin apportionment from Lake Powel to Washington County, UT (i.e., the St. George, UT, area, Basin apportionment from Lake Powel to Washington County, UT (i.e., the St. George, UT, area,
which is technical y located within the Lower Basin drainage area).which is technical y located within the Lower Basin drainage area).~~103~~108 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 has been designated the lead agency for the project Reservoir near St. George, UT. Reclamation has been designated the lead agency for the project
under NEPA and is coordinating an Environmental Impact Statement (EIS) for the most recent under NEPA and is coordinating an Environmental Impact Statement (EIS) for the most recent
proposed version of the project.proposed version of the project.~~104~~109 Supporters in Utah argue that the pipeline is needed to provide Supporters in Utah argue that the pipeline is needed to provide
a second primary water source for the St. George area, in addition to the Virgin River. a second primary water source for the St. George area, in addition to the Virgin River. ~~Opponents~~
~~include the other six Colorado River Basin states, which~~Some environmental groups have argued that the proposed have argued that the proposed
development and diversion of additionaldevelopment and diversion of additional Upper Basin waters is il -advisedUpper Basin waters is il -advised in light of in light of ~~the basin’s~~
climate change and the basin’s issues with over-
~~101~~106 T he projected decrease in revenues is due to, among other factors, the decommissioning of the Navajo Generating T he projected decrease in revenues is due to, among other factors, the decommissioning of the Navajo Generating
Station (whose receipts are one source of incoming revenue accruing to the fund). Station (whose receipts are one source of incoming revenue accruing to the fund).
~~102~~107 T his project was authorized in the Omnibus Public Land Management Act of 2009 ( T his project was authorized in the Omnibus Public Land Management Act of 2009 ( P.L. 111-11), Title X, Part III. P.L. 111-11), Title X, Part III.
~~103~~108 While St. George, UT , is technically within the Lower Colorado River Basin’s drainage, as previously discussed, 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. T hus, the LPP would utilize Upper Utah’s state allocation comes out of waters available to the Upper Basin. T hus, the LPP would utilize Upper ~~Ba sin~~Basin
waters. waters.
~~104~~109 For project NEPA For project NEPA ~~studies~~st udies, see https://www.usbr.gov/uc/DocLibrary/EnvironmentalImpactStatements/, see https://www.usbr.gov/uc/DocLibrary/EnvironmentalImpactStatements/
LakePowellPipeline/index.html#intro. LakePowellPipeline/index.html#intro.
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~~over-~~al ocation. al ocation. ~~They have also opposed~~These groups have argued for major changes to the scope of the EIS.110 The six other Colorado River Basin states have raised concerns related to the proposed LPP’s “legal and operational issues,” and they have raised concerns with the LPP NEPA process as the de facto forum for the LPP NEPA process as the de facto forum for
resolving a conflict among basin statesresolving a conflict among basin states ~~and~~. The six states have requested that Reclamation have requested that Reclamation refrain from issuing refrain from issuing
a final EIS until these issues can be resolved on a consensus basis.a final EIS until these issues can be resolved on a consensus basis.~~105~~111
Drought Contingency Plan Implementation and Future Basin
Agreements
Congress may remain interested in implementation of the Congress may remain interested in implementation of the ~~DCPs~~drought contingency plans and other related agreements, and other related agreements,
including their success or failure at stemming further Colorado River cutbacks and adding including their success or failure at stemming further Colorado River cutbacks and adding
additional water to the basin’s storage reservoirs. Similarly, Congress may be interested in the additional water to the basin’s storage reservoirs. Similarly, Congress may be interested in the
overal hydrologic status of the Colorado River Basin, includingoveral hydrologic status of the Colorado River Basin, including new and new and existing efforts to plan existing efforts to plan
for increased demand in the basin and stretch limited basin water supplies. for increased demand in the basin and stretch limited basin water supplies.
Efforts to renew the 2007 Interim Guidelines (including the DCPs), which expire at the end of Efforts to renew the 2007 Interim Guidelines (including the DCPs), which expire at the end of
2026, 2026, ~~began in 2020 and~~ are expected to be the next major hurdle in the consensus-based are expected to be the next major hurdle in the consensus-based
management of the management of the Colorado River. The status of these Colorado River. The status of these ~~“reconsultation”~~reconsultation efforts, including any efforts, including any
major extensions or major extensions or ~~new agreements to come out of them~~ new/amended agreements, may be key to avoiding future conflict , may be key to avoiding future conflict
over basin resources. over basin resources.

Author Information

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

Disclaimer
This document was prepared by the Congressional Research Service (CRS). CRS serves as nonpartisan This document was prepared by the Congressional Research Service (CRS). CRS serves as nonpartisan
shared staff to congressional committees and Members of Congress. It operates solely at the behest of and shared staff to congressional committees and Members of Congress. It operates solely at the behest of and
under the direction of Congress. Information in a CRS Report should n ot be relied upon for purposes other under the direction of Congress. Information in a CRS Report should n ot be relied upon for purposes other
than public understanding of information that has been provided by CRS to Members of Congress in than public understanding of information that has been provided by CRS to Members of Congress in
connection with CRS’s institutional role. CRS Reports, as a work of the United States Government, are not connection with CRS’s institutional role. CRS Reports, as a work of the United States Government, are not
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~~105~~110 Letter from Utah Rivers Council et al. to Rick Baxter, Program Manager, Bureau of Reclamation Provo Area Office, September 8, 2020. 111 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.
Congressional Research Service Congressional Research Service
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