Does water use in the basin affect the quality of the water resources?
Streamflow regulation and water use for irrigation, hydroelectric power production, and industry affect the water chemistry and biological communities of streams. During the irrigation season, diversions and irrigation returns reduce streamflows and degrade stream-water quality. Storage reservoirs for irrigation, flood control, and hydroelectric power reduce streamflow velocities and stream habitat to the detriment of native biological communities. Irrigated agriculture is the primary consumptive use of water in the basin. About 8 million acre-feet, or 53 percent, of the water used for irrigation in the basin in 1990 was diverted from surface-water supplies. About half of these diversions are from five canals at Lake Walcott and Milner Dam. About 7.1 million acre-feet, or 47 percent, of the total irrigation use was withdrawn from ground water. Some water applied to fields for irrigation returns to streams or infiltrates back to the ground water, transporting nutrients, pesticides, and
