Law of the River

The Law of the River is a complex body of laws, court cases and regulations that control 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 probably the most controlled, controversial and litigated river in the world.

Colorado River Compact

In 1922, seven states negotiated the Colorado River Compact, which divided the states into two basins—upper and lower—and 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 authorized the apportionment of 300,000 acre-feet per year to Nevada, 2.8 MAFY to Arizona, and 4.4 MAFY to California. At the time, Nevada's negotiators viewed 300,000 acre-feet per year as a more than reasonable amount as Southern Nevada had no significant agricultural or industrial users, groundwater seemed plentiful and no one forsaw the population changes that would occur.

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

While compact negotiators estimated the flow of the river to be at least 17 MAFY, today's records indicate a flow of 16.4 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. Still, there is little support in the seven basin states for renegotiating the compact. A new agreement would require approval from each state's legislature and the U.S. Congress.

The 1922 Colorado River Compact also provided the legislative stimulus to harness the river. After much debate, Congress passed legislation to authorize building Hoover Dam. Completed in 1935, the dam was the first giant step toward controlling the rampaging river.