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

March 1, 2019 – April 4, 2024 R45546

Management of the Colorado River: Water
November 1, 2023
Allocations, Drought, and the Federal Role
Charles V. Stern
The Colorado River Basin covers more than 246,000 square miles in seven U.S. states
Specialist in Natural
(Wyoming, Colorado, Utah, New Mexico, Arizona, Nevada, and California) and Mexico.
Resources Policy
Pursuant to federal law, the Bureau of Reclamation (part of the Department of the Interior)

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

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

Compact of 1922, established a framework to apportion water supplies between the river’s Upper
and Lower Basins, divided at Lee Ferry, AZ. The compact allocated 7.5 million acre-feet (MAF)
For a copy of the full report,
annually to each basin, and a 1994 treaty made an additional 1.5 MAF in annual flows available
please call 7-5700 or visit
to Mexico. A Supreme Court case and related decrees inform the Secretary of the Interior’s
www.crs.gov.
management of the delivery of all water below Hoover Dam.
Apportioned Colorado River water exceeds the river’s natural flows, and actual consumptive use plus other water losses (e.g.,
evaporation) typically exceeds flows. This imbalance, coupled with a long-term drought dating to 2000, has stressed basin
water supplies. Reclamation closely tracks the status of two large reservoirs—Lake Powell in the Upper Basin and Lake
Mead in the Lower Basin—as indicators of basin storage conditions. Since the onset of drought in the early 2000s, storage
levels at these reservoirs have fallen. To alleviate these trends, water releases from both lakes have been tied to specific water
storage levels. Since 2020, pursuant to previous agreements, Reclamation has reduced water deliveries in Arizona and
Nevada and reduced its deliveries to Mexico. In the Upper Basin, Lake Powell’s storage also has continued to drop; some
worry this could jeopardize hydropower generation at Glen Canyon Dam. Wet conditions in 2023 improved the short-term
outlook for both reservoirs.
Efforts to Address Drought
The federal government has led multiple efforts to improve the basin’s water supply outlook, resulting in collaborative
agreements in 2003 and 2007 and in the 2019 drought contingency plans (DCPs) for the Upper and Lower Colorado River
Basins. In 2022, due to widespread concern about the basin’s long-term water supplies, Reclamation initiated a process to
revise its near-term operational guidelines for river management. In May 2023, the Department of the Interior and basin
states announced a consensus-based proposal in which the three Lower Basin states will conserve a total of 3 MAF prior to
2026, with 2.3 MAF of these reductions compensated by the federal government using previously appropriated funds.
Reclamation formally adopted this proposal in March 2024.
Most of the agreements to conserve Colorado River Basin water supplies expire in 2026, and Reclamation is currently
leading a process analyzing options for “long-term” (post-2026) operations. To date, Upper and Lower Basin leaders have
been unable to agree on a preferred set of actions to guide long-term basin operations, and have submitted competing plans to
the federal government. Reclamation plans to publish its preferred alternative for long-term operations by late 2024.
Congressional Role
Congress funds and oversees management of basin water and power facilities. Congress has enacted legislation affecting
Colorado River waters (e.g., Indian water rights settlements, new water storage facilities) and authorizing water shortage
mitigation (e.g., the DCPs and other related efforts). Section 50233 of P.L. 117-169 (popularly known as the Inflation
Reduction Act) provided $4.0 billion for drought mitigation in the West. The majority of this funding is being used to
compensate water contractors for recently agreed-upon delivery reductions. Congress may consider further amending existing
authorities or funding mitigation activities for basin water shortages.
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Introduction
From its headwaters in Colorado and Wyoming to its terminus in the Gulf of California, the Colorado
River Basin covers more than 246,000 square miles. The basin spans seven U.S. states (Wyoming,
Colorado, Utah, New Mexico, Arizona, Nevada, and California) and two countries (the United States and
Mexico). Pursuant to federal law, the Bureau of Reclamation (Reclamation), a component of the
Department of the Interior (DOI), plays a prominent role in the management of the basin’s waters. In the
Lower Basin (i.e., Arizona, Nevada, and California), Reclamation also serves as water master on behalf
of the Secretary of the Interior, a role that elevates the status of the federal government in basin water
management.1 The federal role in managing Colorado River water is magnified by the multiple federally
owned and operated water storage and conveyance facilities in the basin, which provide low-cost water
and hydropower supplies.
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,
and recreation, among other uses. A majority of basin water supplies (70%) are used to irrigate 5.5 million
acres of land; basin waters also provide M&I water supplies to nearly 40 million people.2 Much of the
area that depends on the river for its water supplies is outside of the drainage area of the Colorado River
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,
Boulder, and Colorado Springs, CO); Provo, UT; Albuquerque and Santa Fe, NM; and Los Angeles, San
Diego, and the Imperial Valley in Southern California (Figure 1). Colorado River hydropower facilities
can provide up to 4,200 megawatts of electrical power per year.3 The river also provides habitat for a wide
range of species, including several species listed under the federal Endangered Species Act (ESA; 87 Stat.
884, 16 U.S.C. §§1531-1544). It flows through seven national wildlife refuges and 11 National Park
Service (NPS) units; these and other areas of the river support important recreational opportunities.4

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

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

Source: Bureau of Reclamation, Colorado River Basin Water Supply and Demand Study, 2012.
Precipitation and runoff in the basin are highly variable. Water conditions on the river depend largely on
snowmelt in the basin’s northern areas. From 1906 to 2023, natural flows in the Colorado River Basin
averaged about 14.6 million acre-feet (MAF) annually.5 Flows have dipped significantly since 2000;

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

annual natural flows from 2000 to 2023 averaged approximately 12.5 MAF per year.6 According to
Reclamation, the 23-year period from 2000 to 2022 was the driest 23-year period in more than 100 years
of Colorado River record keeping, and among the driest periods in the past 1,200 years.7 Climate change
impacts, including warmer temperatures and altered precipitation patterns, may further increase the
likelihood of prolonged drought in the basin.8
Congress plays a prominent role in the management of the Colorado River. Congress funds and oversees
Reclamation’s management of Colorado River Basin facilities, including facility operations and programs
to protect and restore endangered and threatened species. Congress has also approved and continues to
consider Indian water rights settlements involving Colorado River waters, and development of new and
expanded water storage in the basin. In addition, Congress has approved supplemental funding to mitigate
drought and stretch basin water supplies, and new authorities for Reclamation to combat drought and
enter into agreements with states and those who are contracted to receive water from federal Colorado
River infrastructure (i.e., contractors). 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.
The Law of the River:
Foundational Documents and Programs
The Law of the River refers to a collection of compacts, treaties, statutes, and other authorities that govern
Colorado River allocations and apportionments.9 In the latter part of the 19th century, interested parties in
the Colorado River Basin began to recognize that local interests alone could not solve the challenges
associated with development of the Colorado River. Plans conceived by parties in California’s Imperial
Valley to divert water from the mainstream of the Colorado River were thwarted because these proposals
were subject to the sovereignty of both the United States and Mexico.10 The river also presented
engineering challenges, such as deep canyons and erratic water flows, and economic hurdles that
prevented local or state groups from building the necessary storage facilities and canals to provide an
adequate water supply. In part because local or state groups could not resolve these “national problems,”
Congress considered options to control the Colorado River and resolve potential conflicts between the
states.11 In an effort to resolve these conflicts and avoid litigation, Congress gave its consent for the states
and Reclamation to enter into an agreement to apportion Colorado River water supplies in 1921.12

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

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

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

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

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

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

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

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

National Park values. However, the legislation states that the provisions are not intended to affect state water rights to Colorado
River allocations that have been secured by “any compact, law, or decree.” P.L. 102-575, §1802, 106 Stat. 4669 (1992). The
CRBPA provides that if the federal government fails to comply with applicable law in operating Glen Canyon Dam, any affected
state can sue to enforce its provisions in the Supreme Court. 43 U.S.C. §1551(c).
51 Ibid.
52 Operating Criteria, 70 Federal Register 15,873 (Mar. 29, 2005); Colorado River Reservoirs, Coordinated Long-Range
Operations, 35 Federal Register 8951 (June 10, 1970). Through later legislation, Congress required that, in preparing the LROC
and Annual Operating Plan, the Secretary of the Interior must consult the governors of the basin states and with the public, see
Grand Canyon Protection Act of 1992, P.L. 102-575, §1804(c)(3), 106 Stat. 4669.
53 Statement of Bureau of Reclamation Commissioner Camille Calimlim Touton, in U.S. Congress, Senate Committee on Energy
and Natural Resources, Subcommittee on Water and Power, 117th Cong., 2nd sess., May 25, 2022. For a more detailed discussion
of the effects of long-term drought on Glen Canyon Dam, see CRS Report R47497, Long-Term Drought and Glen Canyon Dam:
Potential Effects on Water Deliveries and Hydropower, by Charles V. Stern and Ashley J. Lawson.
54 The Curecanti Unit was renamed the Aspinall Unit in 1980 in honor of U.S. Representative Wayne N. Aspinall of Colorado.
55 In total, 16 of the 22 Upper Basin projects authorized as part of CRSP have been developed. (Of the six remaining projects,
five were determined by Reclamation to be infeasible, and Congress deauthorized the Pine River Extension Project.) For a
complete list of projects, see Bureau of Reclamation, “Colorado River Storage Project,” at https://www.usbr.gov/uc/rm/crsp/
index.html.
56 Reclamation, “Hoover Dam Frequently Asked Questions and Answers,” at https://www.usbr.gov/lc/hooverdam/faqs/
powerfaq.html, accessed October 30, 2023.
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Imperial Dam (a diversion dam) diverts Colorado River water to the All-American Canal for use in some
of the river’s largest agricultural areas in California’s Imperial and Coachella Valleys.
Annual Operations
Reclamation monitors Colorado River reservoir levels and projects them 24 months into the future in
monthly studies (called 24-month studies).57 The studies take into account forecasted hydrology, 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
future. They express water storage conditions at Lake Mead and Lake Powell in terms of elevation, as feet
above mean sea level.
In addition to the 24-month studies, the CRBPA requires the Secretary of the Interior to transmit to
Congress and the governors of the basin states, by January 1 of each year, an Annual Operating Plan
(AOP). In the AOP, Reclamation describes the actual operation for the preceding operating year and the
projected operation for the coming year.58 The AOP’s projected January 1 water conditions for the
upcoming calendar year establish a baseline for future annual operations.59
Since the adoption of operational guidelines by Reclamation and basin states in 2007 (see section, “2007
Interim Guidelines/Coordinated Operations for Lake Powell and Lake Mead”), Reclamation has tied
operations of Hoover and Glen Canyon Dams to specific pool elevations at Lake Mead and Lake Powell.
For Lake Mead, the first level of shortage (a Tier One Shortage Condition) in the 2007 guidelines, under
which Arizona’s and Nevada’s allocations are curtailments (along with releases to Mexico), is triggered if
the Lake Mead pool elevation falls below 1,075 feet. For Lake Powell, releases under tiered operations
are based on storage levels in both Lake Powell and Lake Mead. Drought contingency plans (DCPs) for
the Upper and Lower Basins, enacted in 2019,60 overlaid additional operational changes tied to elevations
in both reservoirs, including a new Tier Zero shortage beginning at a higher reservoir elevation (up to
1,090 feet) and additional curtailments for other existing tiers (e.g., Tier Two, etc.).61 For Lake Powell, the
Upper Basin DCP incorporated a Drought Response Operations Agreement (DROA) that established a
target lake elevation of 3,525 feet. It also provided for altered releases from Glen Canyon Dam and Upper
Basin reservoirs in order to protect Lake Powell from falling below an elevation that would no longer
produce hydropower. These efforts are discussed more in the below section “Recent Developments and
Agreements.”
Recent Conditions
Since 2020, falling water levels in Lake Mead resulted in Reclamation implementing Lower Colorado
River Basin delivery curtailments for Arizona and Nevada in accordance with previous plans (Table 1).
Water levels in 2020 triggered a Tier Zero reduction, as agreed to in the 2019 DCPs. In August 2021,
Reclamation declared the first-ever Tier One Shortage Condition for the Lower Basin in 2022.62 In August

57 Current 24-month studies, as well as two- and five-year probable projections of Lake Mead and Powell elevations, are
available at Reclamation, “Colorado River System Projections Overview,” at https://www.usbr.gov/lc/region/g4000/riverops/
coriver-projections.html.
58 The operating year for Glen Canyon Dam runs from October 1 through September 30; the operating year for Hoover Dam runs
from January 1 through December 31.
59 Current and historical AOPs are available at Reclamation, “Annual Operating Plan for Colorado River Reservoirs,” at
https://www.usbr.gov/uc/water/rsvrs/ops/aop/.
60 See below section, “2019 Drought Contingency Plans.”
61 For more details, see below section, “Lower Basin Drought Contingency Plan.”
62 Reclamation, “Reclamation Announces 2022 Operating Conditions for Lake Powell and Lake Mead,” press release, August 16,
2021, at https://www.usbr.gov/newsroom/#/news-release/3950.
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2022 Reclamation announced a Tier Two Shortage for 2023, resulting in further water delivery
reductions.63 For 2024, Reclamation forecasted another year of operations under Tier One (i.e., fewer
reductions than in 2023) as a result of improved hydrology and other conservation efforts.64 In 2022 and
early 2023, Lake Powell fell below the target elevation of 3,525 feet, which had not occurred since the
late 1960s.65 As of early 2024, combined storage in both reservoirs had increased relative to 2023 and was
slightly lower than levels seen in 2021.
Table 1. Lower Basin Lake Mead Operational Tiers by Operating Year, 2020-2024
(water delivery curtailments in terms of thousand acre-feet [KAF])
Cumulative Delivery Curtailments by State in
KAF (percentage of total deliveries)
Operational
Year
Tier
Arizona
California
Nevada
2020
Zero
192 (6.8%)
-
8 (2.6%)
2021
Zero
192 (6.8%)
-
8 (2.6%)
2022
One
512 (18.2%)
-
21 (7.0%)
2023
Two
592 (21.1%)
-
25 (8.3%)
2024 (forecast)
One
512 (18.2%)
-
21 (7.0%)
Source: CRS, based on information from the Bureau of Reclamation, 2019-2023.
Notes: The operating year for the Lower Basin runs from January 1 through December 31.
Mitigating the Environmental Effects of Colorado River
Basin Development
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.
§§4321 et seq.) and the ESA. Thus, many of the environmental impacts associated with the development
of basin resources were not originally taken into account. Over time, multiple efforts have been initiated
to mitigate these effects. Some of the highest-profile efforts have been associated with water quality (in
particular, salinity control) and the effects of facility operations on endangered and threatened species.
These efforts are discussed below.
Salinity Control
Salinity and water quality are long-standing issues in the Colorado River Basin. Parts of the Upper Basin
are covered by salt-bearing shale (which increases salt content of water inflows), and salinity content
increases as the river flows downstream due to both natural leaching and return flows from agricultural
irrigation. The 1944 U.S.-Mexico Water Treaty did not set water quality or salinity standards in the
Colorado River Basin. After years of dispute between the United States and Mexico regarding the salinity

63 Reclamation, “Interior Department Announces Actions to Protect Colorado River System, Sets 2023 Operating Conditions for
Lake Powell and Lake Mead,” press release, August 16, 2022, at https://www.usbr.gov/newsroom/news-release/4294.
64 Reclamation, “Reclamation announces 2024 operating conditions for Lake Powell and Lake Mead,” press release, August 15,
2023, at https://www.usbr.gov/newsroom/news-release/4603.
65 Reclamation, “Lake Powell to Temporarily Decline Below 3,525 Feet,” press release, March 4, 2022, at https://www.usbr.gov/
newsroom/#/news-release/4117. 3,525 feet is established as a target because it is 35 feet above 3,490 feet, the level at which
power production would cease.
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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.66 The agreement
guarantees Mexico that the average salinity of its treaty deliveries will be no more than 115 parts per
million higher than the salinity content of the water diverted to the All-American Canal at Imperial Dam
in Southern California. To control the salinity of Colorado River water in accordance with this agreement,
Congress passed the Colorado River Basin Salinity Control Act of 1974, which authorized desalting and
salinity control facilities to improve Colorado River water quality. The most prominent of these facilities
is the Yuma Desalting Plant, which was largely completed in 1992 but has never operated at capacity due
to cost and other factors.67 In 1974, the seven basin states also established water quality standards for
salinity through the Colorado River Basin Salinity Control Forum.68
Endangered Species Efforts and Habitat Improvements
Congress enacted the ESA in 1973. As the federal government listed some basin species under ESA in
accordance with the act,69 federal agencies and nonfederal stakeholders consulted with the U.S. Fish and
Wildlife Service (FWS) to address the conservation of the listed species. As a result of these
consultations, several major programs have been developed to protect and restore listed fish species on
the Colorado River and its tributaries. Summaries of some of the key programs are below.
Upper Colorado Endangered Fish Recovery Program
The Upper Colorado Endangered Fish Recovery Program was established in 1988 to assist in the recovery
of four species of endangered fish in the Upper Colorado River Basin.70 Congress formally authorized this
program in 2000.71 The program is implemented through several stakeholders under a cooperative
agreement signed by the governors of Colorado, Utah, and Wyoming; the Secretary of the Interior; and
the Administrator of WAPA. The recovery goals of the program are to reduce threats to species and
improve their status so they are eventually delisted from the ESA. Some of the actions taken in the past
include providing adequate instream flows for fish and their habitat, restoring habitat, reducing nonnative
fish, augmenting fish populations with stocked fish, and conducting research and monitoring.
Reclamation is the lead federal agency for the program and provides the majority of federal funds for
implementation. Other funding includes a portion of Upper Basin hydropower revenues from WAPA and
funding from FWS; the states of Colorado, Wyoming, and Utah; and water users, among others.

66 See International Boundary and Water Commission, Minute 242, Permanent and Definitive Solution to the International
Problem of the Salinity of the Colorado River, August 30, 1973, at https://www.ibwc.gov/Treaties_Minutes/Minutes.html.
67 The Yuma Desalting Plant’s limited operations have been due in part to the cost of its operations (desalination can require
considerable electricity to operate) and surplus flows in the Colorado River during some years. In lieu of operating the plant,
high-salinity irrigation water has been separated from the United States’ required deliveries to Mexico and disposed of through a
canal that enters Mexico and discharges into wetlands called the Ciénega de Santa Clara, near the Gulf of California. Whether
and how the plant should be operated and how the impacts on the Ciénega de Santa Clara from the untreated irrigation runoff
should be managed remain topics of some debate in the basin and between Mexico and the United States.
68 Additional information about the forum and related salinity control efforts is available at Colorado River Basin, “Salinity
Control Forum,” at https://www.coloradoriversalinity.org/.
69 Several listed species are found throughout the Colorado River Basin. Some are specifically found in the Colorado River, such
as the Razorback sucker (Xyrauchen texanus), Bonytail chub (Gila elegans), Colorado pikeminnow (Ptychocheilus Lucius), and
Humpback chub (Gila cypha). Consultation about an agency action’s effects on these species is required by 16 U.S.C. §1536(a).
70 The fish species are the humpback chub, bonytail, Colorado pikeminnow and razorback sucker. For more information, see
Upper Colorado River Endangered Fish Recovery Program at http://www.coloradoriverrecovery.org/uc. For general background
information on the Endangered Species Act (87 Stat. 884, 16 U.S.C. §§1531-1544), see CRS Report R46677, The Endangered
Species Act: Overview and Implementation.
71 P.L. 106-392.
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San Juan River Basin Recovery Implementation Program
The San Juan River Basin Recovery Implementation Program was established in 1992 to assist in the
recovery of ESA-listed fish species on the San Juan River, the Colorado’s largest tributary.72 The program
is a partnership implemented under a cooperative agreement between DOI and the states of Colorado and
New Mexico, the Jicarilla Apache Nation, the Navajo Nation, the Southern Ute Indian Tribe, and the Ute
Mountain Ute Indian Tribe.73 It is concerned with the recovery of the Razorback sucker (Xyrauchen
texanus) and Colorado pikeminnow (Ptychocheilus Lucius). Congress authorized this program with the
aim to protect the genetic integrity and population of listed species, conserve and restore habitat
(including water quality), reduce nonnative species, and monitor species. The program is coordinated by
FWS, and Reclamation is responsible for operating the Animas-La Plata Project and Navajo Dam on the
San Juan River in a way that reduces effects on the fish populations. The program is funded by a portion
of revenues from hydropower revenues from WAPA in the Upper Basin, Reclamation, the Bureau of
Indian Affairs, and participating states. Recovery efforts for listed fish are coordinated with the Upper
Colorado Endangered Fish Recovery Program.
Glen Canyon Dam Adaptive Management Program
The Glen Canyon Dam Adaptive Management Program was established in 1997 in response to a directive
from Congress under the Grand Canyon Protection Act of 1992 to operate Glen Canyon Dam “in such a
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.”74 This 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 monitoring and
other studies to evaluate the effects of the flows.75 The results are expected to better inform managers how
to provide water deliveries and conserve species.
Lower Colorado Multi-Species Conservation Program
The Multi-Species Conservation Program (MSCP) is a multistakeholder initiative to conserve 27 species
(8 listed under ESA) along the Lower Colorado River while maintaining water and power supplies for
farmers, tribes, industries, and urban residents.76 The MSCP began in 2005 and is planned to last for at
least 50 years.77 The MSCP was created through consultation under ESA. To achieve compliance under
ESA, federal entities involved in managing water supplies in the Lower Colorado River Basin met with
resource agencies from Arizona, California, and Nevada; Native American Tribes; environmental groups;
and recreation interests to develop a program to conserve species along a portion of the Colorado River. A
biological opinion (BiOp) issued by the FWS in 1997 covers operations and maintenance activities
conducted by Reclamation along the Colorado River from Lake Mead to the Southerly International

72 For more information, see U.S. Fish and Wildlife Service, “San Juan River Basin Recovery Implementation Program,” at
https://www.fws.gov/southwest/sjrip/.
73 It also includes participation by water development interests in Colorado and New Mexico.
74 For more information, see Reclamation, Glen Canyon Dam Adaptive Management Program, “Glen Canyon Dam High Flow
Experimental Release,” at https://www.usbr.gov/uc/progact/amp/ltemp.html.
75 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.
76 The stakeholders include 6 federal and state agencies, 6 tribes, and 36 cities and water and power authorities. Stakeholders
serve more than 20 million residents in the region, and irrigate 2 million acres of farmland. For more information, see Lower
Colorado River Multi-Species Conservation Program at https://www.lcrmscp.gov/.
77 The program was authorized under Subtitle E of Title IX of P.L. 111-11.
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Boundary; consultation was reinitiated in 2002, and a new BiOp was issued later that year.78 Nonfederal
stakeholders also applied and received an incidental take permit under Section 10(a) of the ESA for their
activities.79 This resulted in a habitat conservation plan for the MSCP that formed the basis for the
program.80 A Lower Colorado River Multi-Species Conservation Program Implementing Agreement
integrated the federal and nonfederal activities in the MSCP and was signed by stakeholders in 2005.81
The objective of the MSCP is to create habitat for listed species, augment the populations of species listed
under ESA, maintain current and future water diversions and power production, and abide by the
incidental take authorizations for listed species under the ESA. In 2003, the estimated total cost of the
program over its lifetime was approximately $626 million, split evenly between Reclamation (50%) and
the states of California, Nevada, and Arizona (who collectively fund the remaining 50%). The
management and implementation of the MSCP is the 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
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
Development Fund, col ects revenues from the Central Arizona Project (CAP), as well as from a surcharge on revenues
from the Boulder Canyon and Parker-Davis Projects that was enacted under the Hoover Power Plant Act of 1984 (P.L. 98-
381). These revenues are available without further appropriation toward defraying CAP operation and maintenance costs,
salinity control efforts, and funding for Indian water rights settlements identified under the Arizona Water Settlements Act
of 2004 (i.e., funding for water systems of the Gila River Indian Community and the Tohono O’odham Nation, among
others). In the Upper Basin, the Upper Colorado River Basin Fund 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 Program, and endangered fish studies on the Colorado and San Juan rivers, among other things.
Source: Department of the Interior, Department of the Interior Budget Appendix, Fiscal Year 2023 Budget Request.
Tribal Water Rights
Tribal water rights are often senior to other uses on the Colorado River.82 Tribal water diversions based on
these rights typically come out of individual state allocations. There are 30 federally recognized tribes in
the Colorado River Basin, many of whom have settled or unresolved (i.e., currently claimed for use but
unsettled) tribal water rights.83 As of early 2023, 11 basin tribes had reserved (i.e., held for future use)
water rights claims that have not been quantified and settled; the total potential amount of these claims is

78 U.S. Fish and Wildlife Service, Reinitiation of Formal Section 7 Consultation on Lower Colorado River Operations and
Maintenance - Lake Mead to Southerly International Boundary, Arizona, California and Nevada, April 30, 2002, at
https://www.usbr.gov/lc/region/g2000/BO2002operations.pdf.
79 The incidental take permit is valid for 50 years from its date of issuance and covers the implementation of the Lower Colorado
River Multi-Species Conservation Program, diversions of water from the river, demand for and receipt of hydropower, and flow
and non-flow actions along the Colorado River with the geographic scope of the permit.
80 Lower Colorado River Multi-Species Conservation Program, Final Lower Colorado River Multi-Species Conservation
Program Volume II: Habitat Conservation Plan, December 17, 2004, at https://lcrmscp.gov/lcrm-prod/lcrm-prod/pdfs/
hcp_volii_2004.pdf.
81 Lower Colorado River Multi-Species Conservation Program Implementing Agreement at https://lcrmscp.gov/lcrm-prod/lcrm-
prod/pdfs/imp_agr_2005.pdf.
82 Tribal water rights claims typically arise out of the right of many tribes to water resources dating to treaties establishing their
reservations. These water rights are often senior to those of non-Indian water rights holders because they date to the creation of
the reservation (i.e., prior to the awarding of most state water rights). For more information on Indian water rights settlements,
see CRS Report R44148, Indian Water Rights Settlements.
83 For a list of the tribes, see Bureau of Reclamation, “Colorado River Basin,” at https://www.usbr.gov/ColoradoRiverBasin/.
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unknown.84 According to Reclamation, as of December 2020, tribes held diversion rights to
approximately 3.4 MAF per year of Colorado River water.85 Previous studies noted that these tribes were
using just over half of their quantified rights.86
Because of the magnitude and seniority of tribal water rights, future decisions about the settlement and
development of tribal water rights in the Colorado River Basin are likely to influence the availability of
basin water resources for various uses. Increased consumptive water use by tribes with existing quantified
and settled water rights, and/or future settlement of claims and additional consumptive use of basin waters
by tribes with reserved rights, would exacerbate competition for basin water resources. At the same time,
some tribes have entered into arrangements to lease or conserve their waters to other users; new
agreements along these lines have the potential to secure water supplies for some non-tribal users without
other viable alternative sources of water.
Drought and the Supply/Demand Imbalance
The Colorado River Compact was based on the assumption (formed by the available record at the time)
that average annual flows on the river were 16.4 MAF per year.87 However, actual flows have been
considerably less than that (and have dropped further during the ongoing drought). In most years,
consumptive uses and losses (e.g., evaporation) of Colorado River waters exceed the river’s natural flows.
This condition—referred to as the structural deficit—leads to a drawdown of basin reservoirs.
Consumptive use in the basin generally increased from 1971 to 2002 but declined after the 2003 approval
of the Quantitative Settlement Agreement (QSA), which led to a decrease of consumptive use in the
Lower Basin (see below section, “Recent Developments and Agreements”).88 In recent years, demand has
dropped further, although the ongoing drought has continued to stress water supplies.
The lack of a formal mechanism accounting for evaporative losses in the Lower Basin exacerbates the
supply/demand disparity. A key difference between Upper and Lower Basin reporting involves how each
basin accounts for consumptive use. In accordance with Articles I and V of the Arizona v. California
decree,89 a Lower Basin Water Accounting Report (published annually) reports only on diversions from
the system for consumptive use. Conversely, the comparable Upper Basin accounting—the Upper Basin
Consumptive Use and Losses Report (published every five years)—is prepared in response to
congressional direction in the CRBPA, which directed “a detailed breakdown of the beneficial

84 CRS analysis of enacted Indian water rights settlements and Bureau of Reclamation, Colorado River Basin Water Supply and
Demand Study, Technical Report C- Water Demand Assessment, Appendix C9, Tribal Water Demand Scenario Quantification,
Dec. 2012, pp. C9-33–C9-34. Tribes with claims yet to be fully adjudicated or quantified as of early 2023 include the Navajo
Nation; the Ute Indian Tribe of the Uintah and Ouray Reservation; the Havasupai Tribe; the Hopi Tribe; the Kaibab Band of
Paiute Indians; the Pascua Yaqui Tribe; San Carlos Apache Tribe; the San Juan Southern Paiute Tribe; the Tohono O’odham
Nation; Tonto Apache Tribe; and the Yavapai Apache Nation.
85 Reclamation, Review of the Colorado River Interim Guidelines for Lower Basin Shortages and Coordinated Operations for
Lake Powell and Lake Mead, December 2020, p. 14, at https://www.usbr.gov/ColoradoRiverBasin/documents/7d/
7.D.Review_FinalReport_12-18-2020.pdf.
86 Colorado River Research Group, Tribes and Water in the Colorado River Basin, June 2016. According to this study, tribal
consumptive use in 2015 (including leasing of tribal water to non-tribal entities) totaled 1.7 MAF of the 2.9 MAF in recognized
diversion rights at that time.
87 National Research Council, Committee on the Scientific Bases of Colorado River Basin Water Management, Water Science
and Technology Board, Colorado River Basin Water Management: Evaluating and Adjusting to Hydroclimatic Variability, 2007,
at https://www.nap.edu/read/11857/chapter/1.
88 Consumptive use in the Lower Basin (excluding tributaries and evaporative losses) was in excess of 8.4 MAF in 2002 but had
decreased to 6.8 MAF as of 2020.
89 See footnote 25.
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consumptive use of water on a State-by-State basis.”90 Reclamation defines beneficial consumptive use to
include any removal from the system for beneficial consumptive use, which Reclamation defines to
include both diversions and losses from mainstream reservoir evaporation that occur prior to diversions.91
Thus, even though Lower Basin consumptive use is typically below the compact threshold of 7.5 MAF,
the total amount of water regularly exceeds this threshold, after accounting for evaporative losses.
Studies have concluded that Colorado River flows are unlikely to return to 20th century averages and that
future water supply risk is high.92 Overall, natural flows have declined by approximately 20% over the
last century, and one study attributed more than half of this decline to increasing temperatures resulting
from climate change.93 Although there is potential for some precipitation increases in the region due to
climate change, such potential increases are not expected to counteract projected drying resulting from
rising temperatures.94 As a result, most research has projected continuing reduction in runoff through the
mid-21st century.95
Recent Developments and Agreements
Drought conditions throughout the basin have raised concerns about potential negative impacts on water
supplies. Concerns center on what sort of changes to the current water management regime might result if
the Secretary of the Interior were to determine that a shortage condition exists in the Lower Basin. Some
in Upper Basin States are also concerned about the potential for a compact call of Lower Basin states on
Upper Basin states. This is the commonly used term for the hypothetical attempt of Lower Basin states to
force deliveries of Colorado River water under the compact.96
Drought and other uncertainties related to water rights priorities (e.g., potential tribal water rights claims)
spurred the development of several efforts that generally attempted to relieve pressure on basin water
supplies, stabilize storage levels, and provide assurances of available water supplies. Some of the most
prominent developments since the year 2000 (i.e., the beginning of the current drought) are discussed
below.
2003 Quantitative Settlement Agreement
Prior to the 2003 finalization of the QSA, California had been using approximately 5.2 MAF of Colorado
River on average each year (with most of its excess water use attributed to urban areas). Under the QSA,
which is an agreement between several California water districts and DOI, California agreed to reduce its
use to the required 4.4 MAF under the Law of the River.97 It sought to accomplish this aim by quantifying

90 43 U.S.C. §1551.
91 See Bureau of Reclamation, Upper Colorado River Basin Consumptive Uses and Losses Report, 2016-2020, February 2022, p.
6.
92 B. Udall and J. Overpeck, “The Twenty-First Century Colorado River Hot Drought and Implications for the Future,” Water
Resources Research, vol. 53 (February 17, 2017), pp. 2404-2418.
93 Paul C. D. Milly and Krista A. Dunne, “Colorado River Flow Dwindles as Warming-Driven Loss of Reflective Snow
Energizes Evaporation,” Science, vol. 367, no. 6483 (March 13, 2020), pp. 1252-1255. Hereinafter, Milly and Dunne, “Colorado
River Flow Dwindles.” Also see Mu Xiao, Bradley Udall, and Dennis P. Lettenmaier, “On the Causes of Declining Colorado
River Streamflows,” Water Resources Research 54 (2018), pp. 6739-6756.
94 Milly and Dunne, “Colorado River Flow Dwindles.”
95 Jeff Lukas and Elizabeth Payton, eds., Colorado River Basin Climate and Hydrology: State of the Science, Western Water
Assessment, University of Colorado Boulder, 2020.
96 For more background, see Anne Castle and John Fleck, “The Risk of Curtailment under the Colorado River Compact,”
November 20, 2019, at https://ssrn.com/abstract=3483654.
97 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.
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Colorado River entitlement levels of several water contractors; authorizing efforts to conserve additional
water supplies (e.g., the lining of the All-American Canal); and providing for several large-scale, long-
term agriculture-to-urban water transfers. The QSA also committed the state to a path toward restoration
and mitigation related to the Salton Sea in Southern California.98
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 2004.99 IOPP is an administrative
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
calendar year following the overruns, and the paybacks must be made only from “extraordinary
conservation measures” above and beyond normal consumptive use.100
2004 Arizona Water Settlements Act
The 2004 Arizona Water Settlements Act (AWSA) altered the allocation of CAP water in Arizona. It
ratified three water rights settlements (one in each title) between the federal government and the State of
Arizona, the Gila River Indian Community (GRIC), and the Tohono O’odham Nation, respectively.101 For
the state and its CAP water users, the settlement resolved a final repayment cost for CAP by reducing the
water users’ reimbursable repayment obligation from about $2.3 billion to $1.7 billion. Additionally,
Arizona agreed to new tribal and non-tribal allocations of CAP water so that approximately half of CAP’s
annual allotment would be available to Native American tribes in Arizona, at a higher priority than most
other uses. The tribal communities were authorized to lease the water, so long as the water remains within
the state via the state’s water banking authority. The act authorized funds to cover the cost of
infrastructure required to deliver the water to the Indian communities, much of it derived from power
receipts accruing to the Lower Colorado River Basin Development Fund. It also authorized funding for
the study of a potential New Mexico Unit of CAP.
2007 Interim Guidelines/Coordinated Operations for Lake Powell and
Lake Mead
Another development in the basin was the 2007 adoption of the Colorado River Interim Guidelines for
Lower Basin Shortages and the Coordinated Operations for Lake Powell and Lake Mead (2007 Interim
Guidelines). DOI developed the guidelines to implement the LROC, through issuance of the Annual
Operating Plan for Colorado River Reservoirs (AOP), as directed by the 1968 CRBPA.102 Development
of the agreement began in 2005, when, in response to drought in the Southwest and the decline in basin
water storage, the Secretary of the Interior instructed Reclamation to develop coordinated strategies for

98 The Salton Sea is an inland water body in Southern California that was historically sustained by Colorado River irrigation
runoff from the Imperial and Coachella Valleys, but is shrinking. Toxic dust from exposed seabed is a major concern for
surrounding areas. For more information on the Salton Sea, see CRS Report R46625, Salton Sea Restoration.
99 Reclamation, Record of Decision for the Colorado River Water Delivery Agreement, October 10, 2003, pp. 16-19.
100 Ibid.
101 Congress passed the Colorado River Basin Project Act of 1968 and authorized construction of CAP despite significant
uncertainty related to tribal water rights related to the Colorado River. The Gila River, Arizona’s largest tributary of the Colorado
River, runs directly through the Gila River Indian Community, which encompasses approximately 372,000 acres south of and
adjacent to Phoenix. Additionally, the Tohono O’odham Nation possessed reserved water rights near Tucson with the potential to
disrupt that city’s water supplies.
102 Secretary of the Interior, Record of Decision: Colorado River Interim Guidelines for Lower Basin Shortages and the
Coordinated Operations for Lake Powell and Lake Mead, December 2007, p. 4, at https://www.usbr.gov/lc/region/programs/
strategies/RecordofDecision.pdf.
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Colorado River reservoir operations during drought or shortages.103 The resulting guidelines included
criteria for releases from Lakes Mead and Powell determined by “trigger levels” in both reservoirs, as
well as a schedule of Lower Basin curtailments at different operational tiers. For Lake Powell, preset
inflow measurements determine the reservoir’s annual operational “balancing” tier and resulting releases
to Lake Mead. In the Lower Basin, the guidelines stipulated that Arizona and Nevada, which have junior
rights to California, receive reduced allocations if Lake Mead elevations dropped below 1,075 feet. At the
time, it was thought that the 2007 Guidelines would significantly reduce the risk of Lake Mead falling to
an elevation of 1,025 feet.
The 2007 agreement also included for the first time a mechanism by which parties in the Lower Basin
were able to store conserved water in Lake Mead, known as Intentionally Created Surplus (ICS).
Reclamation accounts for this water annually, and the users storing the water may access the surplus in
future years, in accordance with the Law of the River. As of the end of calendar year 2022, the portion of
Lake Mead water in storage that was classified as ICS was 3.04 MAF.104 That is, as of the end of the
2022, approximately one-third of the water stored in Lake Mead was previously conserved ICS volume.
The 2007 guidelines are considered “interim” because they are scheduled to expire in 20 years (i.e., at the
end of 2026). Thus, Reclamation began coordinating a review on the effectiveness of the 2007 guidelines
in 2020, and in 2022, formally initiated the review process for post-2026 operations.105 The review is
expected to encompass negotiations related to renewal of the Upper and Lower Basin DCPs, which are an
overlay on the 2007 guidelines (see below section, “2019 Drought Contingency Plans”).
System Conservation Program
In 2014, Reclamation and several major basin water supply agencies (Central Arizona Water
Conservation District, Southern Nevada Water Authority, Metropolitan Water District of Southern
California, and Denver Water) executed a memorandum of understanding to provide funding for
voluntary conservation projects and reductions of water use. The activities outlined in the memorandum
had the goal of developing new system water,106 to be applied toward storage in Lake Mead, by the end of
2019.107 Congress formally authorized federal participation in these efforts, known as the Pilot System
Conservation Program, in the Energy and Water Development and Related Agencies Appropriations Act,
2015 (P.L. 113-235, Division D). The Energy and Water Development and Related Agencies
Appropriations Act, 2019 (P.L. 115-244, Division A) extended the authority through the end of FY2022,
with the stipulation that Upper Basin agreements could not proceed without the participation of the Upper
Basin states through the Upper Colorado River Commission. The authority was most recently extended
through FY2024 in Division CC of the Consolidated Appropriations Act, FY2023 (P.L. 117-328).
Reclamation estimated that as of the end of 2019, the Lower Basin program had conserved more than

103 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.)
104 Bureau of Reclamation, Colorado River Accounting and Water Use Report, Calendar Year 2022, at https://www.usbr.gov/lc/
region/g4000/wtracct.html.
105 Department of the Interior, Reclamation, “Request for Input on Development of Post-2026 Colorado River Reservoir
Operational Strategies for Lake Powell and Lake Mead Under Historically Low Reservoir Conditions,” 87 Federal Register
37884-37888, June 24, 2022.
106 System water refers to water that is provided to increase water supplies as a whole, without being directed toward additional
consumptive use for specific contractors or water users.
107 Agreement Among the United States of America, Through the Department of the Interior, Bureau of Reclamation, the Central
Arizona Water Conservation District, the Metropolitan Water District of Southern California, Denver Water, and the Southern
Nevada Water Authority, for a Pilot Program for Funding the Creation of Colorado River System Water Through Voluntary
Water Conservation and Reductions in Use, Agreement No. 14-XX-30-W0574, July 30, 2014, at https://www.usbr.gov/lc/region/
programs/PilotSysConsProg/PilotSCPFundingAgreement7-30-2014.pdf.
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175,000 AF of water in Lake Mead, at an average cost of $170 per AF.108 Additional projects also were
carried out in the Upper Basin by the Upper Colorado River Basin Commission; these efforts ended in
2018.109
Minute 319 and Minute 323 Agreements with Mexico110
In 2017, the United States and Mexico signed Minute 323, which extended and replaced elements of a
previous agreement signed in 2012—Minute 319—related to implementation of the 1944 U.S.-Mexico
Water Treaty.111 Minute 323 includes, among other things, options for Mexico to hold water in reserve in
U.S. reservoirs for emergencies and water conservation efforts, as well as U.S. commitments for flows to
support the ecological health of the Colorado River Delta. It also extended the initial Mexican reduction
commitments made under Minute 319 (which were similar in structure to the 2007 reductions negotiated
for Lower Basin states) and established a Binational Water Scarcity Contingency Plan that included
additional reductions that would be triggered if DCPs are approved by U.S. basin states (see the following
section, “2019 Drought Contingency Plans”).
2019 Drought Contingency Plans
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, on March 19, 2019, Reclamation and the Colorado River Basin states finalized DCPs for
both the Upper Basin and the Lower Basin. These plans, which are an overlay of the 2007 Interim
Guidelines discussed above, required final authorization by Congress to be implemented. Congress
approved the plans on April 16, 2019, in the Colorado River Drought Contingency Plan Authorization
Act. Similar to the 2007 guidelines, these plans are scheduled to be in place through 2026. At the time of
their enactment, the combined efforts represented by the DCPs were expected to cut the risk of Colorado
River reservoirs reaching critically low elevations by approximately 50%.112 Each of the basin-level
DCPs is discussed below in more detail.
Upper Basin Drought Contingency Plan
The Upper Basin DCP aims to protect against Lake Powell reaching critically low elevations through
coordinated Upper Basin reservoir operations. It also authorizes storage of conserved water in the Upper
Basin that would serve as the foundation for a water use reduction effort (i.e., a Demand Management
Program) that may be developed in the future.113
Under the Upper Basin DCP’s Drought Response Operations Agreement (DROA), the Upper Basin states
agree to operate system units to keep the surface of Lake Powell above 3,525 feet, which is 35 feet above

108 For individual projects, see Lower Colorado Region, “Pilot System Conservation Program,” at https://www.usbr.gov/lc/
region/programs/PilotSysConsProg/pilotsystem.html. Accessed October 30, 2023.
109 For more information, see Upper Colorado River Commission, “System Conservation Pilot Program,” at
http://www.ucrcommission.com/system-conservation-pilot-program/.
110 For more information on the 1994 U.S.-Mexico Water Treaty and Colorado River water sharing issues with Mexico, see CRS
Report R45430, Sharing the Colorado River and the Rio Grande: Cooperation and Conflict with Mexico, by Nicole T. Carter,
Stephen P. Mulligan, and Charles V. Stern.
111 International Boundary & Water Commission, “Minutes Between the United States and Mexican Sections of the IBWC,” at
https://www.ibwc.gov/Treaties_Minutes/Minutes.html.
112 U.S. Congress, House Committee on Natural Resources, Subcommittee on Water, Oceans, and Wildlife, Oversight Hearing
on the Colorado River Drought Contingency Plan, 116th Cong., 1st sess., March 28, 2019, H.Hrg. 116-10 (Washington: GPO,
2019). Hereinafter, 2019 House Natural Resources DCP Hearing.
113 While such a mechanism exists for the Lower Basin, a comparable program has not been developed in the Upper Basin.
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“minimum power pool” (i.e., 3,490 feet, the minimum elevation needed to run the dam’s hydroelectric
plant). Under DROA, the two main mechanisms to do this are altering the timing of releases from Glen
Canyon Dam and operating “initial unit” reservoirs on the mainstream of the Colorado River (e.g., Navajo
Reservoir, Blue Mesa Reservoir, and Flaming Gorge Reservoir) to protect Lake Powell elevations,
potentially through storage drawdown. Operational changes may occur either through DROA’s emergency
provisions, which allow the Secretary of the Interior to make supplemental water deliveries at his or her
discretion (after consultation with basin states), or through a planning process establishing formal triggers
for Upper Basin water deliveries to Lake Powell, based on agreed-upon hydrological targets.
The other primary component of the Upper Basin DCP, the Upper Basin DCP Demand Management
Program, has not been formally established. It would entail willing seller/buyer agreements allowing for
temporary paid reductions in water use that would provide for more storage volume in Lake Powell. As
noted, the Upper Colorado River Commission operated an Upper Basin System Conservation Pilot
Program from 2015 to 2018; that program compensated water users for temporary, voluntary efforts that
resulted in additional water conserved in Lake Powell. A future Upper Basin DCP Demand Management
Program may expand on some of those efforts.
Due to falling lake levels, Reclamation implemented drought response operations under DROA that led to
reduced storage in other Upper Basin mainstream reservoirs in 2021 and 2022.114 Separately, Reclamation
also began planning efforts under DROA, known as the Drought Response Operations Plan, and
approved this plan in 2022.115 More recently, improved hydrology has boosted Lake Powell storage
(Figure 3).

114 For example, in 2021, 180,000 AF was transferred to Lake Powell from Flaming Gorge Reservoir (125,000 AF), Blue Mesa
Reservoir (36,000 AF), and Navajo Reservoir (20,000 AF).
115 For more information, see Reclamation, Colorado River Basin Drought Contingency Plans, at “Drought Response Operations
Agreement,” at https://www.usbr.gov/dcp/droa.html.
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Figure 3. Lake Powell End-of-Month Elevation Projections
(January/March 2024 24-month study inflow scenarios)

Source: U.S. Bureau of Reclamation, “24-Month Study Projections,” January/March 2024, at https://www.usbr.gov/lc/
region/g4000/riverops/24ms-projections.html.
Notes: WY = Water Year; DROA = Drought Response Operations Agreement.
Lower Basin Drought Contingency Plan
The Lower Basin DCP is designed to require Arizona, California, and Nevada to curtail deliveries and
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
Mead, thereby increasing lake levels. Under the DCP, Nevada and Arizona (which were already set to
have their supplies curtailed beginning at 1,075 feet under the 2007 Interim Guidelines) have committed
to contributing additional supplies to maintain higher lake levels (i.e., beyond previous commitments).
These reductions begin at 1,090 feet and would reach their maximums when reservoir levels drop below
1,025 feet. The Lower Basin DCP includes—for the first time—delivery reductions for California. These
curtailments begin with a 200,000 AF delivery reduction at Lake Mead elevations between 1,040 and
1,045 feet and would increase by 50,000 AF for each additional 5-foot drop in Lake Mead elevation
below 1,040 feet, to as much as 350,000 AF at elevations of 1,025 feet or lower. The curtailments are
categorized in terms of tiers (also sometimes referred to as levels), with Tier One shortage conditions the
term adopted for elevations from 1,050-1,075 feet, and Tier Two shortage conditions the term for
elevations between 1,025 feet and 1,050 feet.
The curtailments in the Lower Basin DCP are in addition to those agreed to under the 2007 Interim
Guidelines and under Minute 323 with Mexico. Specific and cumulative delivery reductions prior to the
latest round of reductions agreed to in 2024 (see below section, “Near-Term Operations: 2023/2024
Supplemental Environmental Impact Statement”) are shown in Table 2. 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 controversial reductions under the
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Lower Basin DCP were committed to by Arizona, where pursuant to previous changes under the 2004
AWSA, a large group of agricultural users were already facing major reductions to their CAP water
supplies prior to the enactment of DCP.
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Table 2. Lower Basin Water Delivery Curtailment Volumes Prior to 2024
(values in thousand acre-feet)
Binational
2007 Interim
Minute 323
Water
Shortage
Delivery
Scarcity
Total Volume of Curtailment
Guidelines
Reductions
DCP Curtailment
Conting. Plan
(% of Lower Colorado River Apportionment)
Lake Mead
Lower
Elevation (ft)
AZ
NV
Mexico
AZ
NV
CA
Mexico
AZ
NV
CA
Basin
Mexico
1,090 ->1,075
0
0
0
192
8
0
41
192 (6.8%)
8 (2.6%)
0 (0%)
200
41
1,075 ->1,050
320
13
50
192
8
0
30
512 (18.2%)
21 (7%)
0 (0%)
533
80
1,050 ->1,045
400
17
70
192
8
0
34
592 (21.1%)
25 (8.3%)
0 (0%)
617
104
1,045 ->1,040
400
17
70
240
10
200
76
640 (22.8%)
27 (9.0%)
200 (4.5%)
867
146
1,040 ->1,035
400
17
70
240
10
250
84
640 (22.8%)
27 (9.0%)
250 (5.6%)
917
154
1,035 ->1,030
400
17
70
240
10
300
92
640 (22.8%)
27 (9.0%)
300 (6.8%)
967
162
1,030 - 1,025
400
17
70
240
10
350
101
640 (22.8%)
27 (9.0%)
350 (7.9%)
1,017
171
<1,025
480
20
125
240
10
350
150
720 (22.8%)
30 (10.0%)
350 (7.9%)
1,100
275
Sources: Table by CRS, using data in the 2007 Interim Shortage Guidelines, Minute 323 between Mexico and the United States, Lower Basin Drought Contingency Plan, and
the Binational Water Scarcity Contingency Plan in Minute 323 between Mexico and the United States.
Notes: Does not reflect additional 2024-2026 curtailments agreed to in the Bureau of Reclamation’s March 2024 Final Supplemental Environmental Impact Statement for
Near-Term Colorado River Operations. (See below section, “Near-Term Operations: 2023/2024 Supplemental Environmental Impact Statement.”)

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In 2019, at the time of the passage of the Colorado River Drought Contingency Plan
Authorization Act, Reclamation asserted that the Lower Basin DCP would significantly reduce
the risk of Lake Mead elevations falling below critical elevation of 1,020 feet.116 Combined with
the commitments from Mexico, total planned reductions under shortage scenarios (i.e., all
commitments to date, combined) were expected to decrease Lower Basin consumptive use by
241,000 AF to 1.375 MAF per year, depending on the curtailments triggered by Lake Mead’s
elevation.117 Despite these efforts, Lake Mead has continued to decline since the Lower Basin
DCP was finalized, and is projected to continue to decline despite improved hydrology in 2023
(Figure 4). These developments have triggered additional Lower Basin conservation efforts.
Figure 4. Lake Mead End of Month Elevation Projections
(January/March 2024 24-month study inflow scenarios)

Source: U.S. Bureau of Reclamation, “24-Month Study Projections,” January/March 2024, at
https://www.usbr.gov/lc/region/g4000/riverops/24ms-projections.html.
Notes: WY = Water Year; DROA = Drought Response Operations Agreement.
Near-Term Operations: 2023/2024 Supplemental Environmental
Impact Statement
Ongoing declines in Lake Mead and Powell highlighted the need for additional “near-term”
operational changes prior to the expiration of existing agreements in 2026. At a June 14, 2022,
Senate hearing, the Commissioner of Reclamation announced that basin states would need to
conserve an additional 2-4 MAF to protect Lake Mead and Lake Powell storage volumes over the

116 2019 House Natural Resources DCP Hearing.
117 For a summary of the curtailments that add up to this amount, see “1,090 - >1,075” row of Table 2.
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2023-2026 period.118 The Commissioner noted that if the targets were not met with voluntary
actions by the states by August 2022, DOI was prepared to act unilaterally.119 No major water
savings commitments were announced in response to Reclamation’s June statement.120
In late October 2022, Reclamation announced its intent to revise the 2007 Interim Guidelines in
2023 and 2024 (i.e., prior to post-2026 operational changes to the guidelines, which are
proceeding separately) to address continued low runoff conditions in the basin. As part of this
process, Reclamation published in the Federal Register its notice of intent to prepare a
supplemental environmental impact statement (SEIS) for changes to the 2007 Interim Guidelines
in three areas: Lake Mead operations during shortage conditions, coordinated operation of Lake
Powell and Lake Mead, and midyear review for implementation of the operational guidelines.121
As part of this process, Reclamation solicited proposals in these areas from the basin states, with
a preference for “consensus” proposals.
On January 31, 2023, all of the basin states except California responded to Reclamation’s notice
with a combined proposal (the Six State Proposal),122 while California submitted its own proposal
(the California Proposal) separately.123 The Six State Proposal requested that Reclamation model
in its SEIS 1.543-1.943 MAF per year in new delivery reductions on Lower Colorado River Basin
contractors, to be implemented through two mechanisms. First, reductions to account for 1.543
MAF of evaporative losses would be allocated among Lower Basin contractors and Mexico, and
would be assessed at most Lake Mead elevations based on stream reach (i.e., position in the basin
relative to bodies of water affected by evaporation) and recent consumptive use levels.124 Second,
additional operational tier changes and delivery reductions are tied to Lake Mead elevations of
1,050 feet and lower.125 For its part, the California Proposal would have included 1.0-1.95 MAF
per year in new delivery reductions for Lower Basin contractors (i.e., not based on evaporation),
depending on Lake Mead elevations. Both state proposals also suggested changes to Lake
Powell’s operational tiers to allow more water to be left in that reservoir, although they would do
so in different ways.

118 U.S. Congress, Senate Committee on Energy and Natural Resources, Short And Long Term Solutions To Extreme
Drought In The Western U.S., Statement of the Honorable Camille Touton, 117th Cong., 2nd sess., June 14, 2022.
Hereinafter, 2022 Drought Hearing. These amounts were based on a 2022 Reclamation analysis. See Reclamation,
“Colorado River System Mid Term Projections,” June 16, 2022, at https://www.usbr.gov/ColoradoRiverBasin/
documents/20220616-ColoradoRiverSystemMid-termProjections-Presentation.pdf.
119 2022 Drought Hearing.
120 In a July 18, 2022, letter to Reclamation, the Upper Colorado River Commission declined to contribute a specific
volume of reductions to these efforts, and instead laid out a five-point plan as the basis for its water conservation
efforts. Letter from Charles Cullom, Director, Upper Colorado River Commission, to Camille Touton, Commissioner,
U.S. Bureau of Reclamation, July 18, 2022, at http://www.ucrcommission.com/wp-content/uploads/2022/07/2022-July-
18-Letter-to-Reclamation.pdf.
121 Bureau of Reclamation, “Notice of Intent To Prepare a Supplemental Environmental Impact Statement for
December 2007 Record of Decision Entitled Colorado River Interim Guidelines for Lower Basin Shortages and
Coordinated Operations For Lake Powell and Lake Mead,” 87 Federal Register 69042, November 17, 2022.
Hereinafter, November 2022 Notice.
122 Letter from Colorado River Basin State Representatives of Arizona, Colorado, Nevada, New Mexico, Utah, and
Wyoming to Tanya Trujillo, Assistant Secretary, Water & Science, U.S. Department of the Interior, January 31, 2023.
Hereinafter, Six State Proposal.
123 Letter from Colorado River Board of California to Deputy Interior Secretary Tommy Beaudreau et al., U.S.
Department of the Interior, January 31, 2023. Hereinafter, California Proposal.
124 This amount also assumes the assessment of evaporative losses on Mexico.
125 Six State Proposal. These reductions would move the current Tier Three reduction schedule (which begins at 1,025
feet) up to a Lake Mead elevation of 1,050 feet, and would institute additional delivery reductions at Lake Mead
elevations of 1,030 feet or lower.
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Reclamation released multiple iterations of its draft SEIS in 2023. In April, it released a draft with
modeling for a “no action” alternative and two action alternatives.126 Both alternatives would
have imposed an equal amount of new reductions in 2024 tied to Lake Mead elevations, with the
primary difference being the approach for apportioning reductions; Action Alternative 1 assumed
reductions based on priority order of water rights (i.e., large curtailments [in terms of percentage]
for Arizona and Nevada), whereas Action Alternative 2 assumed the Secretary would use existing
federal authorities to impose the same percentage-based delivery reductions on all Lower Basin
users (i.e., without regard to senior water rights in California).127 Outside of the approach to
Lower Basin shortage operations, the SEIS action alternatives included similar options in other
areas.128
On May 22, 2023, DOI announced a consensus-based proposal in which the three Lower Basin
states would conserve a total of 3 MAF prior to 2026, with 2.3 MAF of these reductions
compensated by the federal government via $4.0 billion in previously appropriated funds in
budget reconciliation legislation commonly referred to as the Inflation Reduction Act (IRA; P.L.
117-169).129 This proposal included total curtailments of at least 3.0 MAF in operating years
2023 through 2026, on top of existing contributions. The states requested, and DOI agreed, to
temporarily withdraw the April draft SEIS.130 Reclamation released a new draft SEIS in October
2023 and formally adopted the consensus-based alternative on March 5, 2024.131 Table 3 shows
state-level commitments before and after the SEIS.

126 Bureau of Reclamation, Near Term Colorado River Operations, Draft Supplemental Environmental Impact
Statement, April 2023, at https://www.usbr.gov/ColoradoRiverBasin/SEIS.html
127 The Supreme Court has determined the Secretary of the Interior is not bound by a single approach to addressing
Colorado River supply shortages in the Lower Basin. See Arizona v. California, 373 U.S. at 593. The Court stated that
the Secretary may consider reducing Lower Basin deliveries proportionally to statutory allocations of the first 7.5 MAF
(California 4.4/7.5, Arizona 2.8/7.5, and Nevada 0.3/7.5), but the Secretary also has the authority and discretion to elect
an alternate basis for apportioning shortages, subject to statutory constraints. Ibid., pp. 592-593.
128 For instance, both alternatives proposed altering Lake Powell releases so that at lower Lake Powell levels, releases
would be below the compact’s required average of 7.5 MAF per year (potentially as low as 6.0 MAF per year). At Lake
Powell elevations between 3,500 and 3,525 feet, releases to the Lower Basin would be maintained at 6.0 MAF. At
elevations below 3,500 feet, releases could be further reduced.
129 Department of the Interior, “Biden-Harris Administration Announces Historic Consensus System Conservation
Proposal to Protect the Colorado River Basin,” press release, May 22, 2023, at https://www.doi.gov/pressreleases/
biden-harris-administration-announces-historic-consensus-system-conservation-proposal. These funds are discussed
further in the below section, “Funding and Oversight of Existing Facilities and Programs.”
130 Ibid.
131 Bureau of Reclamation, Near-Term Colorado River Operations, Final Supplemental Environmental Impact
Statement, March 5, 2024, https://www.usbr.gov/ColoradoRiverBasin/documents/NearTermColoradoRiverOperations/
20240300-Near-termColoradoRiverOperations-FinalSEIS-508.pdf.
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Table 3. Comparison of Colorado River Curtailments Before and After 2024
Supplemental EIS
(curtailment amounts in thousand acre-feet [KAF])
Pre-2024 Curtailments (2007 ROD, 2019
2024 SEIS Action: 2007 ROD, 2019 DCP,

DCP)
2023 Lower Division Proposal
Lake Mead
Elevation
(Feet)
AZ
NV
CA
Total
AZ
NV
CA
Total
1,090 -
192
8
—
200
472
78
400
950
>1,075
1,075 -
512
21
—
533
792
91
400
1,283
>1,050
1,050 -
592
25
—
617
872
95
400
1,367
>1,045
1,045 -
640
27
200
867
920
97
600
1,617
>1,040
1,040 -
640
27
250
917
920
97
650
1,667
>1,035
1,035 -
640
27
300
967
920
97
700
1,717
>1,030
1,030 -
640
27
350
1,017
920
97
750
1,767
1,025
<1,025
640
27
350
1,100
1,000
100
750
1,850
Source: Bureau of Reclamation, Near-term Colorado River Operations, Final Supplemental Environmental Impact
Statement, March 5, 2024.
Notes: SEIS = Supplemental Environmental Impact Statement; 2007 ROD = Record of Decision for 2007
Interim Shortage Guidelines; 2019 DCP = 2019 Drought Contingency Plan for Lower Colorado River Basin;
Lower Division Proposal = April 2023 Consensus Proposal by Lower Colorado River Basin States.
Long-Term/Post-2026 Operations
Parallel to the process analyzing near-term operational changes, in 2022, Reclamation initiated
efforts to study and recommend alternatives for long-term (post-2026) operations on the Colorado
River.132 Most of the major agreements discussed herein are scheduled to expire in 2026. The
post-2026 operational planning process aims to identify a range of alternatives to be employed in
Colorado River management for decades into the future. If basin interests fail to come to an
agreement on post-2026 operational terms, the federal government, through the Secretary of the
Interior, may opt to propose such terms on a unilateral basis (i.e., similar to what DOI initially
proposed in the spring of 2023 for near-term operations).133

132 More information on Reclamation’s process for post-2026 operational planning is available at
https://www.usbr.gov/ColoradoRiverBasin/post2026/index.html.
133 The Boulder Canyon Project Act of 1928 made the Secretary of the Interior responsible for the distribution (via
contract) of all Colorado River water delivered below Hoover Dam (i.e., the Lower Basin), and authorized such
regulations as necessary to enter into these contracts. Subsequent court decisions confirmed the Secretary’s power to
(continued...)
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Comparison of Recent Long-Term Colorado River Operational
Proposals
Despite reportedly lengthy negotiations, Upper and Lower Basin states were unable to agree on a
consensus-based plan for post-2026 operations in early 2024. As a result, the Upper and Lower
Basins submitted competing plans to Reclamation in March 2024. Reclamation is engaging in
modeling of these and other operational alternatives.134 The Upper and Lower Basin alternatives
are discussed in detail below.
Upper Basin Alternative
The Upper Basin States of Colorado, New Mexico, Utah, and Wyoming submitted their
operational alternative to Reclamation on March 5, 2024.135 The Upper Basin’s proposal departs
from the current operational regime by using combined storage in Lake Powell and Lake Mead to
determine a trigger for Lower Basin delivery reductions (as opposed to only Lake Mead storage
levels dictating said reductions). The alternative does not propose any explicit Upper Basin
delivery reductions.
For Lower Basin delivery reductions, the new trigger would be based on a metric that combines
live Lake Mead and Lake Powell storage with “threshold volumes” in each reservoir:136

This trigger would result in a schedule of Lower Basin delivery reductions that phases in linearly
beginning at 90% and ranges up to 3.9 million AF at the lowest reservoir levels (Table 4).137

apportion surpluses and shortages among and within Lower Basin states; this forms the basis for the designation Lower
Basin water master. No similar authorities were provided for the Upper Basin.
134 In addition to the Upper and Lower Basin alternatives, other entities have submitted long-term operational
alternatives to the federal government. For example, a coalition of conservation organizations known as the Water for
Colorado Coalition submitted its operational alternative, referred to as the Cooperative Conservation Alternative, to
Reclamation on March 29, 2024. For more information, see https://waterforcolorado.org/the-cooperative-conservation-
alternative/.
135 Referred to as the Upper Basin Alternative.
136 Live storage refers to active storage minus deadpool storage (i.e., water that cannot be accessed). Threshold volume
in this context is based on the volume of water in each reservoir that is required to avoid deadpool status at each
reservoir (i.e., the level at which stored water can no longer be released through dam outlet works). The threshold
volumes assumed for the Upper Basin’s alternative are 4.5 million AF for Lake Mead and 4.2 million AF for Lake
Powell, or a combined total of 8.7 million AF.
137 Upper Basin Alternative, p. 3.
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Table 4. 2024 Upper Basin Alternative: Lower Basin Delivery Reductions
(curtailment amounts in million acre-feet [MAF] per year)
October 1 Triggera
Lower Basin Reductions
Description
> 90%
0 MAF
No reductions
90% - 70%
0 - 1.5 MAF
Reductions increase linearly up to 1.5 MAF
70% - 20%
1.5 MAF
Static reductions of 1.5 MAF
20% - 0%
> 1.5 MAF
Static reductions of 1.5 MAF, plus additional
reductions increasing linearly up to 2.4 MAF
Source: Letter from Colorado River Upper Division State Representatives of Colorado, New Mexico, Utah,
and Wyoming to the Honorable Camil e Touton, Commissioner, U.S. Bureau of Reclamation, March 5, 2024.
Notes:
a. October 1 Trigger is calculated using the formula outlined in the Upper Basin Proposal.
For example, using October 1, 2023, Lake Mead and Lake Powell storage levels,138 CRS
calculates that the proposed formula would result in a trigger of 26.5%, or static Lower Basin
reductions of 1.5 million AF (as noted in Table 4):

The Upper Basin Alternative also proposes a schedule for Lake Powell releases based on the
October 1 elevation at the lake (Table 5).139 This is conceptually similar to the current baseline
approach, but specific release amounts would be different under the Upper Basin’s proposal and
under certain conditions would be based on a linear rule curve that would reduce releases as
elevations fall.
Table 5. 2024 Upper Basin Alternative: Lake Powell Operations
(release amounts in million acre-feet [MAF] per year)
Lake Powell October 1
Lake Powell Percentage
Elevation (ft)
Full
Lake Powell Water Year Release
> 3,700
100%
As required by dam safety regulations
3,670 - 3,700
81% - 100%
Linear rule curve: 8.1 - 9.0 MAF
3,510 -– 3,670
20% - 81%
Linear rule curve: 6.0 - 8.1 MAF
< 3,510
< 20%
6.0 MAF
Source: Letter from Colorado River Upper Division State Representatives of Colorado, New Mexico, Utah,
and Wyoming to the Honorable Camil e Touton, Commissioner, U.S. Bureau of Reclamation, March 5, 2024.
The Upper Basin alternative did not provide details on exact releases that would be expected to
result at all Lake Powell elevations under the proposed linear rule curve. Lake Powell’s most
recent October 1 elevation (3,573 feet in 2023) would put it in the 3,510-3,670 foot range of the
Upper Basin Alternative. Based on extrapolation of figures in the Upper Basin Alternative, CRS
calculated that the 2023 October 1 Lake Powell elevation of 3,573 feet would result in releases of

138 Bureau of Reclamation, October 2023 Most Probable 24-Month Study, October 17, https://www.usbr.gov/lc/region/
g4000/24mo/index.html.
139 Upper Basin Alternative, pp 2-3.
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6.83 million AF in 2024, which would be approximately 650,000 AF less than current scheduled
2024 releases of 7.48 million AF.140
Lower Basin Alternative
The Lower Basin states of Arizona, California, and Nevada submitted their long-term operational
alternative to Reclamation on March 6, 2024.141 It proposes changes to the current paradigm for
Colorado River Basin management and includes a shift away from the near-term operational
regime’s reliance on 24-month study forecasts and specific trigger elevations in Lakes Powell and
Lake Mead to dictate operations.142 In lieu of the current system, the proposal envisions
management that relies on percentage-based “total system contents” in seven Colorado River
Basin reservoirs as of August 1 of each year. Four of these reservoirs (Flaming Gorge, Blue Mesa,
Navajo, Powell) are located in the Upper Basin, and three (Mead, Mojave, and Havasu) are
located in the Lower Basin.
The proposal envisions five “zones,” with specific water delivery reduction levels for Lower
Basin states, Upper Basin states, and Mexico,143 associated with four of these zones (Figure 5).144
1. No Reduction Zone. At near-capacity levels (i.e., greater than 69% to 100% of
system contents, as a percentage of capacity) no reductions would be
implemented. Storage has rarely approached these levels over the past decade.
2. Initial Reduction Zone. At system contents of 58% to 69%, Lower Basin users
in Arizona, Nevada, and Mexico would see reduced water deliveries ranging up
to 1.5 million acre-feet (AF) reduction at 58% of system capacity. Reduced
deliveries for the first 300,000 AF of these amounts would be shared among
Arizona, Nevada, and Mexico, with Arizona responsible for 80% of reductions,
Nevada responsible for 3.33% of reductions, and Mexico responsible for 16.67%
of reductions. Incremental reductions above 300,000 AF and less than 1.5 million
AF would be shared under a separate formula that incorporates California, with
43.33% of reductions to Arizona, 36.67% of reductions to California, 3.33% of
reductions to Nevada, and 16.67% of reductions to Mexico.
3. Static Reduction Zone. At system contents of 38% to less than 58%, the
reduction on Lower Basin states and Mexico would be a flat 1.5 million AF,
distributed in the amount of 760,000 AF (50.67%) to Arizona, 440,000 AF
(29.33%) to California, 50,000 AF (3.33%) to Nevada, and 250,000 AF (16.67%)
to Mexico.145
4. Basin-Wide Reduction Zone. At system contents of 23% to less than 38%,
water delivery reductions would range from 1.5 million AF at 38% to 3.9 million
AF at 23%, with all reductions in excess of 1.5 million AF (which would

140 Based on the Upper Basin Alternative, CRS calculated a linear release reduction of 13,125 AF per foot of reduced
Lake Powell elevation within this operational tear.
141 Referred to as the Lower Basin Alternative. The Lower Basin Alternative notes that it includes assumptions
regarding participation by Mexico but recognizes that this participation is determined in a separate process. See Lower
Basin Alternative, p. 2.
142 Lower Basin Alternative, p. 2.
143 The proposal acknowledges that proposed totals for Mexico are subject to international negotiations and have not
been finalized.
144 Lower Basin Alternative, attachment pp 1-4.
145 While there are no reductions to Upper Division states in this zone, a small portion of Arizona is in the Upper Basin
and, as a result, Arizona receives some waters from the Upper Basin allocation.
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continue to be shared as per the Static Reduction Zone) shared equally between
Lower Division States and Mexico, and Upper Division States.
5. Basin-Wide Maximum Reduction Zone. At critically low levels (i.e., system
contents of less than 23%), total delivery reductions would continue at the Basin-
Wide Reduction Zone’s lowest level of 3.9 million AF. Thus, the maximum total
delivery reduction on Lower Division States and Mexico in this zone (i.e., the
above reductions scheduled for 23% of system contents) would be approximately
2.7 million AF (the initial 1.5 million AF, plus half of the remaining 2.4 million
AF), while the maximum reduction for Upper Division States would be 1.2
million AF (the other half of the needed 2.4 million AF).
Figure 5. 2024 Lower Basin Alternative: System Storage Reduction Zones
(curtailment amounts in million acre-feet [MAF] per year)

Source: Letter from Colorado River Basin States Representatives of Arizona, California, and Nevada to the
Honorable Camil e Touton, Commissioner, U.S. Bureau of Reclamation, March 6, 2024.
Notes: Percentages reference percentage of total system capacity in use for seven mainstream Colorado River
reservoirs: Flaming Gorge, Blue Mesa, Navajo, Powell, Mead, Mojave, and Havasu.
For the most recent year (August 1, 2023), total basin storage percentage of capacity (i.e., the
comparable live metric for the Lower Basin alternative) under the proposed metric was 44%; the
comparable statistic for the same date in 2022 was 33%.146 (2023 storage was among the lowest

146 CRS analysis of Bureau of Reclamation, ‘Archived Operation Plan for Colorado River System Reservoirs,”
https://www.usbr.gov/lc/region/g4000/24mo/index.html.
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levels on record.) As of early March 2024, system storage under this statistic stood at 42%.147
Applied hypothetically, the August 2023 figure would trigger operations within the proposed
Static Reduction Zone.
Similar to its proposed triggers for Lower Basin curtailments, the Lower Basin Alternative would
revise Lake Powell releases to tie them to total system capacity, with most releases (i.e.,
30%-80% of system capacity) assumed to occur within a “hydrologic shortage” band that ties
releases to a three-year moving average for Upper Basin depletions (Table 6).148 Generally within
this schedule, as Upper Basin use and/or water availability decreases, required releases from Lake
Powell decrease.
Table 6. 2024 Lower Basin Alternative: Lake Powell Operations
(release amounts in million acre-feet [MAF] per year)
Total System Capacity
Lake Powell Water Year Release
< 80%
Equalization Release: Balance the contents of Lakes Powell and Mead as
closely as practicable with releases between 8.5 MAF and 11.0 MAF
30% - 80%
Hydrologic Shortage-Based Release: Releases vary in a stepwise fashion
between 7.0 MAF and 8.5 MAF depending on the extent of Upper Basin
hydrologic shortage:

3-Year Avg Upper Basin Depletions Release
< 3.8 MAF 7.0 MAF
3.81 - 4.3 MAF 7.5 MAF
4.31 - 4.8 MAF 8.0 MAF
> 4.8 MAF 8.5 MAF
20% - 30%
Reduced Release Ramp: Releases of 6.0 MAF to 7.0 MAF determined as a
linear function.
< 20%
Static Release: Releases of 6.0 MAF
Source: CRS, based on letter from Colorado River Upper Division State Representatives of Colorado, New
Mexico, Utah, and Wyoming to the Honorable Camil e Touton, Commissioner, U.S. Bureau of Reclamation,
March 5, 2024.
Notes: Percentages reference percent of total system capacity in use for seven mainstream Colorado River
reservoirs: Flaming Gorge, Blue Mesa, Navajo, Powell, Mead, Mojave, and Havasu.
As noted above, October 1, 2023, system contents under the comparable statistic were 43%,
which would trigger releases in the “hydrologic shortage” range of 7.0 MAF to 8.5 MAF. From
2018 to 2020 (the three most current years available) average Upper Basin consumptive use was
4.2 million AF, which if applied to the 2023 system content figure would trigger Lake Powell
releases of 7.5 million AF.149

147 CRS analysis of Bureau of Reclamation, “Upper and Lower Colorado River Storage Data,” https://www.usbr.gov/
uc/water/basin/index.html, and https://www.usbr.gov/lc/region/g4000/TeacupDiagram.html.
148 Lower Basin Alternative, attachment pp. 4-7.
149 Bureau of Reclamation, Upper Colorado River Basin Consumptive Uses and Losses Report, 2016-2020, February
2022, https://www.usbr.gov/uc/DocLibrary/Reports/ConsumptiveUsesLosses/20220214-
ProvisionalUpperColoradoRiverBasin2016-2020-CULReport-508-UCRO.pdf.
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Issues for Congress
Funding and Oversight of Existing Facilities and Programs
The principal role of Congress as it relates to storage facilities on the Colorado River is funding
and oversight of facility operations, construction, and programs to protect and restore listed
species (e.g., Glen Canyon Dam Adaptive Management Program and the Upper Colorado River
Endangered Fish Program). In the Upper Basin, Colorado River facilities include the 17 active
participating units in the Colorado River Storage Projects, as well as the Navajo-Gallup Water
Supply Project. In the Lower Basin, major facilities include the Salt River Project and Theodore
Roosevelt Dam, Hoover Dam and All-American Canal, Yuma and Gila Projects, Parker-Davis
Project, Central Arizona Project, and Robert B. Griffith Project (now Southern Nevada Water
System).
Congressional appropriations in support of Colorado River projects and programs typically
account for a portion of overall project budgets. For example, in FY2020, approximately 40% of
Lower Colorado River Region’s overall budget was funded with discretionary appropriations,
with the remainder of funding coming from power revenues (which are made available without
further appropriation) and nonfederal partners.150 Congress has also authorized and appropriated
funding for the Colorado River Basin in general (e.g., the Pilot System Conservation Plan).
Congress has also addressed Colorado River funding outside of the regular appropriations
process. In the 117th Congress, in Section 50233 of the IRA Congress provided $4.0 billion for
projects that mitigate drought in the 17 arid and semiarid reclamation states in the West,151 with
priority given to Colorado River Basin activities. This funding is available through FY2026 and
may be used for a variety of activities, including some of the previously authorized activities
discussed above and as compensation for new delivery reductions. Reclamation announced initial
plans for this funding on October 12, 2022, in the form of a new program, the Lower Colorado
River Basin System Conservation and Efficiency Program.152 The program has three components:
• Under the first component (1a), Colorado River water delivery contractors or
entitlement holders submitted proposals resulting in water remaining in Lake
Mead at a set price of $330 per acre-foot for a one-year agreement, $365 per
acre-foot for a two-year agreement, and $400 per acre-foot for a three-year
agreement. These proposals were due in November 2022.
• For the second component (1b), Reclamation accepted proposals for additional
water conservation and efficiency projects that could involve a variety of pricing
options as proposed by Colorado River water delivery contractors or entitlement
holders. These proposals were due in November 2022.
• For the third component (2), Reclamation accepted proposals for long-term
system efficiency improvements that will result in multi-year system
conservation. These proposals were due in August 2023.

150 Reclamation, Lower Colorado Region Annual Report, Fiscal Years 2019 & 2020.
151 Reclamation states refers to the 17 states designated by Congress to be in the Reclamation service area, pursuant to
the Reclamation Act of 1902, as amended. 34 Stat. 259.
152 Bureau of Reclamation, “Biden-Harris Administration Announces New Steps for Drought Mitigation Funding from
Inflation Reduction Act,” Press Release, October 12, 2022, at https://www.usbr.gov/newsroom/news-release/4353.
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To date, Reclamation has announced a number of water savings agreements using the IRA funds
(in particular under components 1a and 1b),153 but the full magnitude of water savings that will
result from these voluntary agreements remains unclear. If the agreements are successful,
additional federal funding similar to that provided in the IRA may be requested in the future to
mitigate the effect of long-term drought in the basin and reduce consumptive use from recent
levels.
In addition to the aforementioned new program being implemented with IRA funding, the
Administration also announced that $250 million of the act’s funding would go toward Salton Sea
restoration activities over the 2022-2026 timeframe.154 Restoration of the Sea is a priority of the
Imperial Irrigation District, one of the largest water rights holders on the Colorado River.155
Tribal Water Rights Settlements and Leasing
Many tribal water rights are senior to other water rights in the basin, and thus are likely to play an
important role in the future of the Colorado River. The extent to which tribes develop their water
rights, or are willing and able to market their water to other users, has ramifications for water
availability in the basin. The 117th Congress authorized a new Indian water rights settlement
related to one tribe’s rights to Colorado River water (the Hualapai Settlement) and enacted a new
authority for the Colorado River Indian Tribes, one of the largest water rights holders on the river,
to enter into agreements to lease a portion of the tribes’ Colorado River water (the Colorado River
Indian Tribes Water Resiliency Act of 2022).156
As previously noted, Congress has approved Indian water rights settlements associated with more
than 2.5 MAF of tribal diversion rights on the Colorado River (these rights are a subset of the
water allocations per state in which they are located); a portion of this water has been developed
to date. Congress may be asked to fund new or upgraded infrastructure to develop existing tribal
water rights, as well as to consider new settlements that would add to the existing tribal
diversions. Some potential Colorado River water rights settlements, such as the settlement of the
water rights claims of the Navajo Nation and the Hopi Tribe for the waters of the Little Colorado
River and the Colorado River in the state of Arizona, have not been enacted.157
New Facilities and Other Alterations
Some states may pursue further development of their unused Colorado River water (i.e., rather
than cutting their use). For example, one project that would develop Upper Basin waters, the
proposed Lake Powell Pipeline (LPP), would direct approximately 86,000 AF of Utah’s Upper

153 As of March 2024, the Administration reported use of $670.2 million in Inflation Reduction Act funds on 24
conservation agreements across California and Arizona; these agreements were expected to conserve up to 1.58 MAF
of water through 2026. Department of the Interior, “Biden-Harris Administration Announces Major Milestone to
Protect Short-Term Stability of Colorado River Basin,” press release, March 5, 2024, https://www.doi.gov/
pressreleases/biden-harris-administration-announces-major-milestone-protect-short-term-stability.
154 Bureau of Reclamation, “Inflation Reduction Act Funds Landmark Agreements to Accelerate Salton Sea
Restoration,” Press Release, November 28, 2022, at https://www.usbr.gov/newsroom/news-release/4380.
155 For more on Salton Sea restoration, see CRS In Focus IF11104, Salton Sea Management and Restoration Efforts, by
Pervaze A. Sheikh and Charles V. Stern. For more on Imperial Irrigation District’s position on the Salton Sea, see
https://www.iid.com/water/salton-sea.
156 Prior to the legislation’s enactment, these tribes, who were awarded their water rights under the Arizona v.
California decree, were not able to lease their water. This is not the case for most other tribes with Colorado River
water rights.
157 This legislation was introduced, but not enacted, in the 112th Congress in H.R. 4067 and S. 2103.
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Basin Colorado River Basin annual apportionment from Lake Powell to Washington County, UT
(i.e., the St. George, UT, area, which is technically located within the Lower Basin drainage
area).158 The pipeline would begin near Glen Canyon Dam in Arizona and would run through
Arizona and Utah to Sand Hollow Reservoir near St. George, UT. Reclamation is the lead agency
for the project under NEPA and is coordinating an environmental impact statement (EIS) for the
most recently proposed version of the project.159
The debate over the Lake Powell Pipeline is illustrative of the issues future water development
proposals may face in the basin. Supporters argue that the pipeline is needed to provide a
secondary water source for the St. George area (in addition to its primary water source from the
Virgin River). However, environmental groups have argued that the proposed development and
diversion of additional Upper Basin waters is ill-advised in light of climate change and the basin’s
over-allocation.160 The six other Colorado River Basin states have raised concerns related to the
proposed LPP’s “legal and operational issues,” and have criticized the use of the LPP NEPA
process as a de facto forum for resolving a conflict among basin states. The six states previously
requested that Reclamation refrain from issuing a final EIS until these issues can be resolved on a
consensus basis.161
Some groups that oppose new infrastructure development on the Colorado River also have
proposed demolition of existing infrastructure, in particular Glen Canyon Dam. They argue that
removing the dam would be beneficial to listed species and the Grand Canyon’s ecosystem and
would be a cheaper and less politically problematic option than other options (e.g., fallowing
Upper Basin farms to conserve water).162 Water and power users and most governmental entities
oppose these efforts for their potential negative economic impact. Reclamation reports that it is
accelerating maintenance actions at Glen Canyon Dam to determine the reliability of using river
bypass tubes at the dam to enable Lower Basin releases at storage levels below minimum power
pool.163 Reclamation is also studying the efficacy of physical modifications to Glen Canyon Dam
to allow for releases below critical elevations.164 Removing or significantly altering Glen Canyon
Dam would likely require authorization by Congress.
Concluding Observations
There is wide acknowledgement that existing directives for managing Colorado River Basin
waters are inadequate to address the ongoing persistent drought and water uses and do not
account for the basin’s current and projected hydrology. The original basis for the Colorado River
Compact assumed more water than turned out to be available for consumptive uses, and drought
in the basin has exacerbated this issue. Although recent agreements have reduced usage, basin-

158 While St. George, UT, is technically within the Lower Colorado River Basin’s drainage, Utah’s state allocation
comes out of waters available to the Upper Basin. Thus, the LPP would utilize Upper Basin waters.
159 For project NEPA documents and studies, see https://www.usbr.gov/uc/DocLibrary/
EnvironmentalImpactStatements/LakePowellPipeline/index.html#intro.
160 Letter from Utah Rivers Council et al. to Rick Baxter, Program Manager, Bureau of Reclamation Provo Area Office,
September 8, 2020.
161 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.
162 Save the Colorado, “Save the Colorado’s Policies for Renegotiation of the 2007 Interim Guidelines for Management
of the Colorado River,” Press Release, November 29, 2022.
163 Bureau of Reclamation, “Interior Department Announces Actions to Protect Colorado River System, Sets 2023
Operating Conditions for Lake Powell and Lake Mead,” August 16, 2022.
164 Ibid.
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wide consumptive use (including evaporation) has continued to exceed natural flows in most
years. The resulting drawdown of basin storage has threatened both hydropower production and
water deliveries. Long-term flow projections estimate that available supplies will continue to
decrease, whereas new demands and diversions (e.g., development of tribal water rights) suggest
that competition for this water among users will continue to increase.
Despite agreement that some level of water delivery reductions will be necessary to protect power
generation and reservoir storage, there remain considerable differences of opinion as to what form
these actions should take. The question of which entities to subject to water delivery reductions
and of what magnitude, as well as what sort of mitigation might accompany these efforts, take on
an added level of urgency due to the river’s economic importance to many areas. The relative
importance of established water rights priorities in the basin, compared to priority for health,
safety, and other uses, is a central issue currently facing decisionmakers. Other questions—
including how much funding, if any, federal and state governments should provide users to forgo
water deliveries—are also likely to figure prominently into future discussions. Changes to
infrastructure and alterations to basin accounting are other likely items for debate in future basin
negotiations.

Author Information

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

Pervaze A. Sheikh

Specialist in Natural Resources Policy

Disclaimer
This document was prepared by the Congressional Research Service (CRS). CRS serves as nonpartisan
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Congressional Research Service
R45546 · VERSION 38 · UPDATED
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