<P> This is a list of dams on the Colorado River system of the southwestern United States and northwestern Mexico . The Colorado runs 1,450 mi (2,330 km) from the Rocky Mountains to the Gulf of California, draining parts of seven U.S. states and two Mexican states . The river system is one of the most heavily developed in the world, with fifteen dams on the main stem of the Colorado and hundreds more on tributaries . Collectively, dams in the Colorado River basin can hold four to five times the river's annual flow, generating hydroelectricity and supplying irrigation and municipal water for over 35 million people . </P> <P> Dams on tributaries are listed if they are taller than 250 ft (76 m), store more than 50,000 acre ft (62,000 dam), or are otherwise historically notable . Tributary dams are organized into two lists; those in the Upper Basin, defined as the half of the Colorado River basin above Lee's Ferry, Arizona, and the Lower Basin . The Upper Basin include such tributary systems as the Green, Gunnison and San Juan . Tributaries in the Lower Basin include the Little Colorado, Virgin and Gila . A key tributary of the San Juan River, the Animas River, was severely affected by the EPA's accidental August 2015 Gold King Mine waste water spill . </P>

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