The Law of the RiverThe Colorado River is managed and operated under numerous compacts, federal laws, court decisions and decrees, contracts, and regulatory guidelines collectively known as the "Law of the River." This collection of documents apportions the water and regulates the use and management of the Colorado River among the seven basin states and Mexico. Following is a synopsis of the most significant documents (you can click on the highlighted titles to get the full text of these regulations in Adobe Acrobat pdf file formats):
- The Colorado River Compact of 1922 - The cornerstone of the "Law of the River", this Compact was
negotiated by the seven Colorado River Basin states and the federal government in 1922. It defined the
relationship between the upper basin states, where most of the river's water supply originates, and the lower
basin states, where most of the water demands were developing. At the time, the upper basin states were
concerned that plans for Hoover Dam and other water development projects in the lower basin would, under
the Western water law doctrine of prior appropriation, deprive them of their ability to use the river's flows in
The states could not agree on how the waters of the Colorado River Basin should be allocated among them, so the Secretary of Commerce Herbert Hoover suggested the basin be divided into an upper and lower half, with each basin having the right to develop and use 7.5 million acre-feet (maf) of river water annually. This approach reserved water for future upper basin development and allowed planning and development in the lower basin to proceed.
- The Boulder Canyon Project Act of 1928 - This act: (1) ratified the 1922 Compact; (2) authorized the
construction of Hoover Dam and related irrigation facilities in the lower Basin; (3) apportioned the lower
basin's 7.5 maf among the states of Arizona (2.8 maf), California (4.4 maf) and Nevada (0.3 maf); and
(4) authorized and directed the Secretary of the Interior to function as the sole contracting authority for
Colorado River water use in the lower basin.
- California Seven Party Agreement of 1931 - This agreement helped settle the long-standing conflict
between California agricultural and municipal interests over Colorado River water priorities. The seven
principal claimants - Palo Verde Irrigation District, Yuma Project, Imperial Irrigation District, Coachella
Valley Irrigation District, Metropolitan Water District, and the City and County of San Diego - reached
consensus in the amounts of water to be allocated on an annual basis to each entity. Although the
agreement did not resolve all priority issues, these regulations were also incorporated in the major
California water delivery contracts.
- The Mexican Water Treaty of 1944 - Committed 1.5 maf of the river's annual flow to Mexico.
- Upper Colorado River Basin Compact of 1948 - Created the Upper Colorado River Commission
and apportioned the Upper Basin's 7.5 maf among Colorado (51.75 percent), New Mexico (11.25 percent),
Utah (23 percent), and Wyoming (14 percent); the portion of Arizona that lies within the Upper Colorado
Basin was also apportioned 50,000 acre-feet annually.
- Colorado River Storage Project of 1956 - Provided a comprehensive Upper Basin-wide water resource
development plan and authorized the construction of Glen Canyon, Flaming Gorge, Navajo and
Curecanti dams for river regulation and power production, as well as several projects for irrigation
and other uses.
- The Arizona v. California U.S. Supreme Court Decision of 1964 - In 1963, the Supreme Court issued a
decision settling a 25-year-old dispute between Arizona and California. The dispute stemmed from
Arizona's desire to build the Central Arizona Project so it could use its full Colorado River apportionment.
California objected and argued that Arizona's use of water from the Gila River, a Colorado River tributary,
constituted use of its Colorado River apportionment, and that it had developed a historical use of some
of Arizona's apportionment, which, under the doctrine of prior appropriation, precluded Arizona from
developing the project.
The Supreme Court rejected California's arguments, ruling that lower basin states have a right to appropriate and use tributary flows before the tributary co-mingles with the Colorado River, and that the doctrine of prior appropriation did not apply to apportionments in the lower basin.
In 1964, the Court issued its decree. This decree enjoined the Secretary of the Interior from delivering water outside the framework of apportionments defined by the law and mandated the preparation of annual reports documenting the uses of water in the three lower basin states.
In 1979, the Supreme Court issued a Supplemental Decree which addressed present perfected rights referred to in the Colorado River Compact and in the Boulder Canyon Project Act. These rights are entitlements essentially established under state law, and have priority over later contract entitlements.
- The Colorado River Basin Project Act of 1968 - This Act authorized construction of a number of water
development projects in both the upper and lower basins, including the Central Arizona Project (CAP).
It also made the priority of the CAP water supply subordinate to California's apportionment in times of
shortage, and directed the Secretary to prepare, in consultation with the Colorado River Basin states,
long-range operating criteria for the Colorado River reservoir system.
- The Criteria for Coordinated Long-Range Operation of Colorado River Reservoirs of 1970 (amended March 21, 2005) - Provided
for the coordinated operation of reservoirs in the upper and lower basins and set conditions for water
releases from Lake Powell and Lake Mead.
- Minute 242 of the U.S.-Mexico International Boundary and Water Commission of 1973 - Required the
U.S. to take actions to reduce the salinity of water being delivered to Mexico at Morelos Dam.
- The Colorado River Basin Salinity Control Act of 1974 - Authorized desalting and salinity control
projects, including the Yuma Desalting Plant, to improve Colorado River quality.
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Updated: March 2008