[1] It loops northwest, then northeast through Yamanashi, before following a generally southerly course to exit into Sagami Bay of the Pacific Ocean between the cities of Hiratsuka and Chigasaki.

As the river crosses Kanagawa, it forms natural levees in the soft soils of the alluvial plains of central Kanagawa's Sagamino plateau, and forms almost no river delta as it exits into the ocean.

The potential of the upper reaches of the Sagami River 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, and the growing need for a reliable supply of drinking and industrial water.

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

In the post war period, the Shiroyama Dam was also completed on the main stream of the Sagami River in 1965.