Law of the River


The 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 inAdobe Acrobat pdf file formats):
Quick Links

Colorado River Compact
Boulder Canyon Project Act
California Seven Party Agreement
Mexican Water Treaty
Upper Colorado River Basin Compact
Colorado River Storage Project
Arizona v. Calif Supreme Court Decision
Supplemental Decree
Consolidated Decree 
Colorado River Basin Project Act
Long Range Operating Criteria 
Minute 242
Colorado River Basin Salinity Control Act 

  • 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 future.

    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 Act 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.

    On March 27, 2006, the Supreme Court issued a Consolidated Decree to provide a single reference to the provisions of the original 1964 decrees and several subsequent decrees (1966, 1979, 1984, and 2000) that stemmed from the original ruling. This decree also reflects the settlements of the federal reserved water rights claim for the Fort Yuma Indian Reservation.

  • 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 - 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.

    On March 21, 2005, following a public review process, including consultation with the seven Colorado River Basin States and other interested parties and stakeholders, the Secretary of the Interior made a number of limited modifications to the text of the 1970 operating Criteria.The associated Federal Register notice annotates the modifications and describes the public process and comments that resulted in the changes.

  • 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.

Several other laws, contracts and documents are part of the "Law of the River," many of which can be found in "Updating the Hoover Dam Documents" - available on-line in the Western Water Digital Library hosted by the University of Utah. A new book - "The Colorado River Documents 2008" - that discusses the Interior Secretary's management of the Colorado River from 1979 through 2008 was published in December 2010, and is available for purchase through the Government Printing Office.

In addition to these provisions, the federal Endangered Species Act and various Native American water claim settlements affect the extent to which water developments and diversions can be utilized in the Colorado River Basin.


Last Updated: 6/30/15