two offstream reservoirs west of Oroville. These two facilities are collectively known as the Oroville–Thermalito Complex. Water is diverted into the upper Thermalito reservoir (Thermalito Forebay) via the Thermalito Diversion Dam on the Feather River. During periods of off-peak power use, surplus energy generated at Hyatt is used to lift water from Thermalito's lower reservoir (the Thermalito Afterbay) to the forebay, which releases water back into the afterbay to generate up to 114 MW of power at times of high demand. The Hyatt and Thermalito plants produce an average of 2,200 gigawatt hours (GWh) of electricity each year, about half of the total power produced by the SWP's eight hydroelectric facilities. Water supply Water released from Oroville Dam travels down the Feather River before joining with the Sacramento River, eventually reaching the Sacramento-San Joaquin Delta, where the SWP's California Aqueduct diverts the fresh water for transport to the arid San Joaquin Valley and Southern California. Oroville–Thermalito hydroelectric facilities furnish about one-third of the power necessary to drive the pumps that lift the water in the aqueduct from the delta into the valley, and then from the valley over the Tehachapi Mountains into coastal Southern California. Water and power from the dam contribute to the irrigation of in the arid San Joaquin Valley Westside and municipal supplies to some 25 million people. At least of water is released. Flood control During the winter and early spring, Lake Oroville is required to have at least , or a fifth of the reservoir's storage capacity, available for flood control. The dam is operated to maintain an objective flood-control release of , which may be further reduced during large storms when flows below the Feather's confluence with the Yuba River exceed . In the particularly devastating flood of 1997, inflows to the reservoir hit more than , but dam operators managed to limit the outflow to , sparing large regions of the Sacramento Valley from flooding. Feather River Fish Hatchery Oroville Dam completely blocks the anadromous migrations of Chinook salmon and steelhead trout in the Feather River. In 1967, in an effort to compensate for lost habitat, the DWR and the California Department of Fish and Game completed the Feather River Fish Hatchery. The Fish Barrier Dam, built in 1962, intercepts salmon and trout before they reach the base of the impassable Thermalito Diversion Dam and forces them to swim up a fish ladder