The mouth of the river was seen by Francisco de Ulloa in 1539 the lower part was explored by Hernando de Alarcón in 1540. The river flows through c.1,000 mi (1,610 km) of canyons, including Arizona's Grand Canyon many national parks, monuments, and recreational areas lie along its banks. The Colorado's waters are used for power and irrigation, especially by means of the Colorado River storage project, the Colorado–Big Thompson project , Hoover Dam , Davis Dam, Imperial Dam, the All-American Canal , Parker Dam , Glen Canyon Dam , and, in Mexico, the Morelos Dam.
Controversies over water rights on the Colorado have long raged between the United States and Mexico and among the bordering states (it supplies most of S California's water) treaties and compacts regulate the river's use. California and, to a lesser degree, Nevada have in the past drawn more water than they were designated to receive. A new compact in 2003 gave California 14 years to reduce its water usage to its legal limits. A greater problem, however, is that the 1922 Colorado River Compact that established the division of water use between the upper and lower basins was based on an estimate of the average annual flow that is 10% to 25% higher than long-term data suggest, due to the use of river gauge data from what is now known to be a relatively wet period in the river basin's history. A 2007 accord established guidelines for reducing allocations in the lower basin when shortfalls occur.
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.
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