In early 1921, the seven Colorado River Basin States authorized the appointment of commissioners to negotiate a compact for the apportionment of the water supply of the river and its tributaries. Congress allowed the states to negotiate a compact under the leadership of then Secretary of Commerce Herbert Hoover as representative of the United States. An agreement was negotiated and signed by the seven appointed commissioners from each of the Colorado River Basin States in November of 1922.

The Compact divided the Colorado River Basin into the Upper Basin and Lower Basin which are defined as those states or parts of states from which waters naturally drain into the Colorado River above and below Lee Ferry, respectively. Lee Ferry is a point on the mainstream of the River, downstream of the historic "Lee's Ferry Gaging Station," and approximately one mile below the mouth of the Paria River in northern Arizona.

The Compact apportioned, in perpetuity to the Upper Basin and to the Lower Basin, the exclusive beneficial consumptive use of 7.5 million acre-feet of water annually. The Lower Basin was given the right to increase its then current beneficial consumptive use by one million acre-feet annually. The Compact further provided that the two basins would share any burden, which might arise because of a water treaty with Mexico, equally. The Upper Basin was required to restrict its use so that the flow of the river at Lee Ferry would not be depleted below an aggregate of 75,000,000 acre-feet for any period of ten consecutive years. The Compact also established a preference for agriculture and domestic uses over water use for power generation:  1922 Colorado River Compact.

This Act authorized the construction of Hoover Dam and Power Plant and the All-American Canal. In addition, the Lower Basin States made provision for the sharing of water, and authorization was given to the Secretary of the Interior (Secretary) to execute contracts for water made available by the Boulder Canyon Project, subject to the terms of the Colorado River Compact.

The provisions of the Act stipulated that it would take effect upon the fulfillment of either of two conditions. The first provision required that all seven states ratify the Colorado River Compact. Because Arizona was not satisfied with the terms of the Compact, it became impossible to meet this condition. In fact, Arizona did not ratify the Colorado River Compact until 1944. The second condition required that six of the states, including California, ratify the Compact, and that California agree to limit its consumptive use of water from the Colorado River to 4.4 million acre-feet. With the exception of Arizona, all of the Colorado River Basin States ratified the Compact, and passage of The California Limitation Act of 1929 completed the conditions required to make the Act effective. President Herbert Hoover declared the Boulder Canyon Project Act and the Colorado River Compact in effect on June 25, 1929.

The Act also authorized the states of Arizona, California and Nevada to enter into an agreement whereby the 7.5 million acre-feet of water that was apportioned to the Lower Basin by Article 111(a) of the Colorado River Compact would be apportioned as follows: to California, 4.4 million acre-feet per annum; to Arizona, 2.8 million acre-feet per annum; and to Nevada, 0.3 million acre-feet per annum. The three states, however, were unable to agree on such an apportionment: 1928 Boulder Canyon Project Act.

The water treaty between the United States and Mexico involving waters of the Colorado River (and the Rio Grande and Tijuana Rivers) became effective November 8, 1945. The Treaty allocated to Mexico 1.5 million acre-feet of Colorado R

iver system waters annually. The allocation was to be increased in years of surplus to 1.7 million acre-feet and reduced proportionately during years of extraordinary drought. The Treaty dealt with quantity and was silent on the quality of water to be delivered.

In 1962, the Mexican Government formally protested to the United States Government regarding the quality of Colorado River water that was being delivered to the Mexicali Valley. Upon the request of the State Department, the governors of the seven Colorado River Basin States reconstituted the Committee of Fourteen (two water experts from each of the seven Basin States appointed by their respective governors) to advise the State Department and the International Boundary and Water Commission about Mexican water salinity issues and potential solutions.

Numerous meetings and negotiations led to the adoption of Minute 242, executed in 1973, which obligates the United States to implement measures that will maintain the salinity of the Colorado River waters delivered to Mexico at nearly the same quality as that diverted at Imperial Dam for use within the United States:  1944 Mexican Treaty.

This Compact, dated October 11, 1948, divided the water apportioned to the Upper Basin by the Colorado River Compact between the five states having territory in the Upper Basin. Arizona was allocated 50,000 acre-feet per annum with the remainder of the Upper Basin entitlement divided according to the following percentages: Colorado, 51.75; New Mexico, 11.25; Utah, 23.00; and Wyoming, 14.00:  1948 Upper Basin Compact

The 1964 Decree reaffirmed the apportionment of the first 7,500,000 acre-feet per annum of Colorado River mainstream water available to the three Lower Basin States as follows: Arizona, 2,800,000; California, 4,400,000; and Nevada, 300,000. Any excess above 7,500,000 acre-feet was apportioned 50 percent to California and 50 percent to Arizona, except that Nevada was given the right to contract for 4 percent of the excess, which would come out of Arizona’s share. The Court left the allocation of shortages to the discretion of the Secretary after providing for satisfaction of present perfected rights in the order of their priority dates. Present Perfected Rights (PPRs) were defined as rights existing and used prior to June 25, 1929, the effective date of the Boulder Canyon Project Act:  1964 AZ v CA Decree

This Act authorized the CAP and other water development projects in the Upper Basin. The CAP was to provide the necessary conveyance and storage facilities to import a major portion of Arizona’s remaining share of Colorado River water into the south-central part of the State. The Act also directed the Secretary to prepare long-range water resources studies directed toward the augmentation of the Colorado River, to prepare criteria for the coordinated long-range operation of the Colorado River reservoirs, and to undertake programs for water salvage and groundwater recovery along and adjacent to the mainstream of the Colorado River.

This Act also declared that the satisfaction of the requirements of the Mexican Water Treaty from the Colorado River constituted a national obligation, which shall be the first obligation of any water augmentation project planned pursuant to the Act and authorized by the Congress. This provision of the Act is very important to the states of the Colorado River Basin, and to Arizona in particular, because of the shortage provision described above.

The Act also directed the Secretary of the Interior to propose criteria for the coordinated long-range operation of federal reservoirs in the Colorado River Basin. These criteria were subsequently developed in cooperation with the Colorado River Basin States and were adopted by the Secretary on June 8, 1970:  1968 Colorado River Basin Project Act