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Los Angeles experienced a major shortage of water in 1900. Since the local well systems could no longer meet the demand for water, a decision was made to import water from high-precipitation areas via aqueducts. The water needs of Los Angeles were satisfied via the Los Angeles Aqueduct, which extends north into the Owens Valley all the way to Mono Lake. 1913 the first aqueduct from the Owens Valley, 375 km long, had been completed. Thereafter, additional water reservoirs and canals were built to secure the water supply for the Los Angeles metropolitan area.

In 1940 the aqueduct was extended northwards to a total of 540 km, reaching up to Mono Lake, where it could tap additional creeks of the eastern Sierra. Dams were built (Grant Lake and in the Long Valley, were the Crowley Lake Reservoir was developed). From the Owens Valley the water crosses mountains, canyons, the Mojave Desert, and 142 tunnels until it reaches Los Angeles. Due to the constantly growing water demands a second water pipeline was built in 1970, which runs parallel to the first aqueduct. The Los Angeles Aqueduct has a transport capacity of 555 million m³. The two aqueducts together take care of about 70% of Los Angeles' need for water.

The rest is being taken care of by the California aqueduct (State Water Project; finished in 1973), the Colorado River aqueduct (finished in 1941), sources and ground water.