Metropolitan Water District of Southern California
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"The Colorado is neither the biggest nor the longest river in the American West, nor, except for certain sections described in the nineteenth-century journals as "awful" or "appalling," is it the most scenic. Its impressiveness and importance have to do with other things…it is the most legislated, most debated, and most litigated river in the entire world. It also has more people, more industry, and a more significant economy dependent on it than any comparable river in the world."

--Marc Reisner, Cadillac Desert, P. 120

They called it a killer. Time and time again, it proved itself wild and unpredictable. To most, it seemed an adversary that could not be defeated.

The Colorado River is the principal water resource in the arid Pacific Southwest. It spans 1,440 miles. Its drainage encompasses 244,000 square miles and includes portions of seven states and the Republic of Mexico. These seven states are identified as the Upper Basin states and the Lower Basin states. The Upper Basin states include Colorado, New Mexico, Utah, and Wyoming, and the Lower Basin states include Arizona, California, and Nevada.

The Colorado River plays an important role for each of the seven states of the Colorado River Basin and Mexico. From 1918 to 1921, the upper and lower states were unable to resolve their differences. Each state wanted to establish its own limits on use of Colorado River water. Each has attempted to secure its citizen's maximum rights for the use of this lifeline of the Southwest.

ColRivmap.jpg (38751 bytes)Out of these attempts has arisen a body of interstate compacts, federal laws, water contracts, state laws, a treaty and other agreements with Mexico, Supreme Court decrees and federal and state administrative actions.
Together, these documents and their interpretation are generally referred to as "The Law of the River" and they control its operations and the rights and priorities for the use of Colorado River water.
"The Law of the River" is based on a concept that apportions the use of water between the Upper and Lower Basins and among states. It also outlines a priority system for the use of Colorado River water. The apportionment and priority concept is comprehensive in dealing with the waters of the river, designating quantities and priorities for use within each of the states, and identifying which state will be charged with the use involved. The 1922 Colorado River Compact is the foundation for "The Law of the River".  

This compact was signed on November 24, 1922 and divided the Colorado River Basin into Upper and Lower basins at Lee Ferry, Arizona. Its negotiators apportioned 7.5 million acre-feet (af) of annual use to each basin and gave the Lower Basin the option to use an additional 1 million af in a year.

As a result of a historic U.S. Supreme Court case in 1963, California’s dependable supply from the Colorado River was reduced to its basic apportionment of 4.4 million af per year. The U.S. Secretary of the Interior was designated "watermaster" for the lower Colorado River with authority to determine if and when surplus or shortage conditions exist. Metropolitan’s firm supplies of Colorado River water were reduced by more than half, effective in 1985 when the Central Arizona Project (CAP) commenced deliveries. For more than half a century, the Colorado River Aqueduct (CRA) has been part of the backbone of the Southern California economy. Constructed and operated by Metropolitan, deliveries through the CRA began in 1941 and in recent decades more than 1.2 million af per year of vital water supplies to the region have been provided.

California’s annual use of Colorado River water has varied from 4.5 to 5.2 million af over the last ten years. Historic and current use of up to 5.2 million af per year stems from the occurrence of surplus conditions and the availability of water apportioned to but unused by Arizona and Nevada. However, Arizona is approaching full use of its basic apportionment, thereby reducing the likelihood that unused water that has been available to Metropolitan and other California water users will continue to be available.

coloradoslide.jpg (8312 bytes)Since 1964, California has made significant investments to offset the eventual reduction in available Colorado River water.  These investments have included developing additional sources of imported water, conservation (demand reduction and use-efficiency improvements), surface and groundwater storage, local supplies, conjunctive-use programs, reclaimed water projects, and recovery and treatment of contaminated groundwater.

While these investments have significantly increased supplies and reduced demand for imported water, they have not been adequate to offset the reduction of Colorado River water to 4.4 million af per year. This reality has fueled further efforts to maximize the beneficial use of California’s river water through cooperative Colorado River conservation programs and transfers of conserved water.

The challenge is to effect these changes and still maintain the productivity of major urban and agricultural centers.

Page updated: August 6, 2007