Colorado River

The Colorado River watershed serves as a primary water source for millions of people living in seven western states, including the state of California.

In 1922, negotiations began on a multi-state compact to allocate the waters of the Colorado River between seven Upper and Lower Basin states.  It was eventually agreed that each basin would receive 7.5 million acre-feet of water per year.  A while later, the Lower Basin states (California, Nevada and Arizona) further allocated their 7.5 million acre-feet allocation as follows:

California – 4.4 million acre-feet

Arizona – 2.8 million acre-feet

Nevada – 300,000 acre-feet

In 1931, the California Seven-Party Agreement divided California’s 4.4 million acre-feet allotment, plus any excess, among the seven major water users in the state.  In 2003, the Quantification Settlement Agreement further quantified provisions of the California Seven-Party Agreement and allowed for agriculture to urban water transfers.

The Palo Verde Irrigation District, Yuma Project-Reservoir Division, Imperial Irrigation District and Coachella Valley Water District are collectively entitled to 3.85 million acre-feet per year.  The remaining 550,000 acre-feet is reserved for MWD, who can also call on another 662,000 acre-feet when adequate water is available.  The City of Long Beach purchases approximately 40 percent of its drinking water supply from MWD, with the rest coming from local groundwater supplies.

In 2010, the legality of the QSA was challenged in court.  If the QSA is ultimately deemed unconstitutional, the reliability of the Colorado River as a future water supply for California will be dramatically reduced.

Water from the Colorado River reaches southern California through the Colorado River Aqueduct (CRA), a 242-mile long water conveyance system capable of transporting 1.3 million acre-feet of water per year.

The CRA was built from 1933 to 1941 by the Metropolitan Water District of Southern California (MWD) in order to supply water to the 13 southern California cities that were founding member agencies of MWD.  The time, manpower and engineering required to complete the massive aqueduct was considerable.


The construction of the Hoover Dam was completed in 1937.  In doing so, it created Lake Mead, which holds millions of acre-feet of Colorado River water.  For over a decade, the Colorado River watershed has experienced severe drought, which has caused the water elevation in Lake Mead to drop by over 130 feet in that same period of time.

On November 4, 2010, the elevation in Lake Mead reached 1,082.07 feet, the lowest level ever since the completion of the Hoover Dam.  When the Lake drops below 1,075 feet, it will trigger the first ever Colorado River allocation shortage, reducing water to the states of Nevada and Arizona.  Additional drops would eventually impact California’s water supply allocation.

It is absolutely essential that users of Colorado River water understand how precarious of a situation now exists on the river.  This source can no longer be considered 100 percent reliable, which should persuade people to permanently change their water use habits so that wasteful and inefficient water uses are no longer tolerated.