Work on the Sagami Dam, the first dam on the main stream of the Sagami River began in 1938; however, lack of funding and the advent of World War II delayed completion until after the end of the war.

It was designed to provide flood control, and industrial and drinking water to the cities of Yokohama, Kawasaki, Yokosuka and the Shōnan area.

It also serves as a Pumped-storage hydroelectricity facility in conjunction with the Honzawa Dam further upstream.

The reversible turbine generators at the Shiroyama Power Plant were designed to function as either electrical power generators, or as pumps, to reverse the flow of water back into the reservoir of the Honzawa Dam in times of low demand.

Lake Tsukui (津久井湖, Tsukui-ko) created by the dam is a major leisure destination in Kanagawa Prefecture, popular with boaters, fishers and campers.