Summary table Law of the River

Summary of selected laws and treaties that make up the Law of the River

Adapted from the "Summary of the Law of the Colorado River" tables, pp. 21-27, in Kwon and Gimbel (2021).

Law	Key provisions/effects	Relevance
Colorado River Compact (1922)	7.5 maf/yr allocated to each of the Upper Basin and the Lower Basin. Upper Basin and Lower Basin are equally responsible for any future allocation to Mexico if not met by surplus above their own 7.5 maf/yr allocations. The Upper Basin will not cause the flow at Lee Ferry to be depleted below 75 maf for any consecutive ten year period.	The Lower Basin has fully developed its Colorado River allocation; the Upper Basin has not. A future failure of the Upper Basin meet the “non-depletion” clause could trigger a “Compact Call” by the Lower Basin.
Boulder Canyon Project Act (1928)	Congressionally ratified the Colorado River Compact and agreed to limit California to 4.4 maf. Authorized the building of the Hoover Dam and the All-American Canal; authorized the Secretary of the Interior as the Water Master in the Lower Basin. Suggested Lower Basin apportionments: CA: 4.4 maf AZ: 2.8 maf NV: 0.3 maf	Serves as the foundation for the management of Lower Basin water.
U.S.-Mexico Water Treaty (1944)	Appropriates 1.5 maf/yr to Mexico; an additional 0.2 maf if surplus supply; Mexico must share in shortage in case of “extraordinary drought.”	Considered the first priority that must be met on the Colorado River
U.S.-Mexico Water Treaty Minutes (1946-present)	Minutes are used to clarify the implementation of the terms of the 1944 Treaty. A total of 150 minutes have been signed to date, notably: 242: Salinity Control 306: Environmental considerations 319: Cooperative measures to address variable Colorado River water supplies 323: Extends and clarifies Minute 319 to 2026	Minutes 319 and 323 are especially significant for creating the mechanism for “pulse flows” through the Colorado River Delta.
Upper Colorado River Basin Compact (1948)	Sets forth Upper Basin apportionment: Arizona receives 50,000 acre-feet Colorado: 51.75% of UB total New Mexico: 11.25% Wyoming: 14% Utah: 23% Establishes Upper Colorado River Commission.	The actual water supply available to these percentages changes based on hydrology and water storage. Arizona is the only state to receive a flat water volume.
Colorado River Storage Project Act (1956)	Congress commits funding to develop Colorado River water in the Upper Basin. Approved Glen Canyon Dam (Lake Powell), Flaming Gorge Dam and Reservoir, Navajo Dam and Reservoir, Blue Mesa Dam and Reservoir. Authorized participating projects and hydropower revenues.	Directive for federal assistance to develop water in the Upper Basin. Serves to authorize storage facilities and promote water use.
Arizona v. California (1963, 1964)	1963 Supreme Court Decision Affirms the allocation of Lower Basin water made by the 1928 Boulder Canyon Project Act Determines the allocation of reserved waters for five Tribes in the basin 1964 Decree Affirms Secretary of the Interior’s operational authority over water in the Lower Basin Any surplus water to be split: CA: 50% AZ: 46% NV: 4% Even under shortage conditions, CA still receives full 4.4 maf/yr	Established the expectation that Lower Basin states will not have reservoir evaporation or water conveyance losses (currently ~1.2 maf/yr) counted against their 7.5 maf/yr allocation.
Colorado River Basin Project Act (1968)	Congress authorizes construction of the Central Arizona Project. Establishes coordinated operations of federal storage facilities in the Boulder Canyon Project Act (e.g., Mead) and Colorado River Storage Project Act (e.g., Powell) by setting release priorities: Releases to supply half of any deficiency for the Mexico Treaty Releases to provide 7.5 maf to the Lower Basin Storage of water in the Upper Basin to assure the two first two priorities are met in the future. Releases to meet additional uses in Lower Basin so long as Powell storage is not less than Mead, to equalize storage in Powell and Mead, or to avoid fill-and-spills from Powell.	The calculation for determining the storage in (3) is the subject of disagreement between the Upper and Lower Basins. Excess releases beyond those needed to meet priorities (1-3) are known as “equalization releases.”
Long Range Operating Criteria (1970) Reclamation rules	Reclamation establishes criteria for the coordinated operation of the Colorado River Storage Project (e.g., Powell) and Lake Mead. Sets the “minimum objective release” from Lake Powell at 8.23 maf.	8.23 maf determined by prorating the the Upper Basin non-depletion requirement of 75 maf over 10 years (7.5 maf/yr), subtracting tributary inflows below Glen Canyon Dam and above Lee Ferry (0.02 maf), and adding half of the U.S.-Mexico Treaty allocation (0.75 maf). Affirmed notion of “normal”, “surplus”, and “shortage” years set up by 1968 CRBPA act, but silent as to how “surplus” and “shortage” years would be identified.
Interim Guidelines for Lower Basin Shortages and Coordinated Operations of Lake Powell and Lake Mead (2007)	Clarifies the definition of a “shortage” condition under which less than 7.5 maf/yr would be released from Lake Mead for Lower Basin users. Sets storage tiers for Powell under which different volume releases will be made, contingent on levels of Powell and Mead. Authorizes mechanisms for the storage in Lake Mead and future delivery of water that is conserved by Lower Basin users (“Intentionally Created Surplus”).	The Interim Guidelines came about after rapidly declining levels of Powell and Mead in the wake of severe drought from 2000-2004 showed inadequacies of the 1970 Long Range Operating Criteria. Equalization releases from Powell during years in the late 2000s and 2010s when both Powell and Mead were well below full capacity, while allowable under the Interim Guidelines, were controversial in the Upper Basin.
Drought Contingency Plans (DCPs; 2019) Interstate agreements	Separate plans for the Upper and Lower Basin provide an overlay to the 2007 Interim Guidelines. Lower Basin DCP commits to implementing conservation measures or to accepting additional delivery reductions from Lake Mead. Upper Basin DCP (i) promotes weather modification to augment supplies; (ii) protects minimum power pool elevation at Lake Powell through upstream releases; (iii) investigates ‘demand management’ program to reduce UB use and store conserved water in Powell.	Under the Lower Basin DCP, in 2021 and 2022 the LB states took delivery reductions of 200 kaf beyond what the 2007 Interim Guidelines stipulated. DCP-imposed delivery reductions in future years may be greater. Under the Upper Basin DCP (ii), Reclamation has made additional releases from Flaming Gorge and Blue Mesa to help protect critical elevations of Lake Powell. Demand management program was piloted in Colorado but was controversial among water users.