Kumagai Gumi
The potential of the Sagami River valley for hydroelectric power development began to be developed in the 1930s, with the growth of industry and electrical consumption in the Yokohama-Kanagawa industrial belt. 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. Work on the Shiroyama Dam, in the former town of Tsukui, Tsukui District commenced in 1960 and was completed in 1965 by the Kumagai Gumi construction company.