The Imperial Reservoir is an artificial lake formed by the construction of the Imperial Diversion Dam across the Colorado River in the Lower Colorado River Valley of Imperial County, California, and Yuma County, Arizona. Partially included in the Imperial National Wildlife Refuge, the reservoir is northeast of Yuma, Arizona. Dry wash watersheds Dry washes are the major watershed feed systems to Imperial Reservoir. The next upstream major watershed feeder is the Bill Williams River from western Arizona. Upstream on the Colorado River, the basic feeder watershed to Imperial Reservoir is the Havasu-Mojave Lakes Watershed of Lake Havasu. Two dry wash watershed attempt to enter the Imperial Reservoir from western Arizona, south of the Bill Williams River: the Bouse and Tyson Washes. Both washes end on the eastern perimeter of the Colorado River Indian Reservation along the Colorado River. Neither enters the river properly, except in the extreme flood stage. No "lengthy" watersheds flow eastwards from California; all are short distances, in the extreme aridity of this desert region. See also List of dams and reservoirs in California List of lakes in California References External links Imperial Reservoir Watershed Map Reservoirs in Yuma County, Arizona National Wildlife Refuges in Arizona Reservoirs in Imperial County, California Colorado River Reservoirs in California Reservoirs in Arizona Reservoirs in Southern California