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State Water Project
In 1960, California voters approved financing for construction of the initial features of the State Water Project (SWP). The project includes some 22 dams and reservoirs, a Delta pumping plant, a 444-mile-long aqueduct that carries water from the Delta through the San Joaquin Valley to southern California. The project begins at Oroville Dam on the Feather River and ends at Lake Perris near Riverside. At the Tehachapi Mountains, giant pumps lift the water from the California Aqueduct some 2,000 feet over the mountains and into southern California.
The SWP provides irrigation water to farms in the San Joaquin Valley, and is a major source of supply for cities in Los Angeles, Riverside, San Bernardino, San Diego, and other parts of southern California. In addition, the SWP serves cities in Napa and Solano counties through the North Bay Aqueduct, Santa Barbara and San Luis Obispo counties through the Coastal Aqueduct and communities in Alameda and Santa Clara counties through the South Bay Aqueduct. The project is operated by the California Department of Water Resources.
The Colorado RiverThe 1,440-mile-long Colorado River passes through parts of seven states, several Indian reservations and the Republic of Mexico. California is entitled to 4.4 million acre-feet of water annually from river. Most of that water irrigates crops in the Palo Verde, Imperial and Coachella valleys, located in the southeastern corner of the state, but the Colorado also is a vital source of water for urban southern California. Urban supplies are distributed by the Metropolitan Water District of Southern California through its Colorado River Aqueduct. MWD is a water wholesale agency that supplies water to water districts that serve 18 million customers in Los Angeles, Orange, San Diego, Riverside, San Bernardino and Ventura counties.
About 30 percent of California's total annual water supply comes from groundwater in normal years, and up to 60 percent in drought years. Local communities' usage may be different; many areas rely exclusively on groundwater while others use only surface water supplies. Contrary to popular opinion, groundwater does not exist in underground lakes. Groundwater fills pores (spaces) between sand, gravel, silt and clay in water-bearing formations known as aquifers.