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Southern Nevada Water Authority

Colorado River Law

Colorado River

A complex body of laws, court cases
and regulations govern the use of the
Colorado River.

A complex body of laws, court cases and regulations known as the “Law of the River” control the use of Colorado River water and the operation of its dams.

In the 1800s, states diverted water from the Colorado River and its tributaries without restrictions. As the diversions increased, a long battle over apportionment evolved. Today, the Colorado River is among the most controlled, controversial and litigated rivers in the world.


In 1922, seven western states negotiated the Colorado River Compact, which divided the states into two basins: Upper Basin and Lower Basin. The compact apportioned 7.5 million acre-feet per year (MAFY) to each basin.

The Upper Basin includes Colorado, New Mexico, Utah and Wyoming. The Lower Basin includes Arizona, California and Nevada.

The 1928 Boulder Canyon Project Act awarded Nevada 300,000 acre-feet per year (AFY), the smallest Colorado River allocation. At the time, Nevada’s negotiators viewed 300,000 AFY as more than reasonable as Southern Nevada had no significant agricultural or industrial users, groundwater seemed plentiful, and the area’s small population was not anticipated to grow significantly.

The compact also referenced Mexico’s right to Colorado River water. In 1944, the United States signed a treaty in which it agreed to deliver an annual quantity of 1.5 MAFY to Mexico.

Average River Flows

Compact negotiators estimated the flow of the river to be at least 17 MAFY and allocated 16.5 MAFY per year for use by the seven western states and Mexico.

Today’s records indicate an average flow of 14.9 MAFY at Lee’s Ferry, just below Lake Powell. Consequently, the sum of the actual compact apportionments and the Mexican treaty exceed the flow of the river in most years. In addition, a sustained drought has reduced significantly the average run-off into the Colorado River.

Despite the reduction in water flowing into the river, there is little support among the seven states sharing the water to renegotiate the compact. A new agreement would require approval from each state’s legislature and the U.S. Congress.


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