Lower Monumental Dam

Lower Monumental Lock and Dam is a hydroelectric, concrete, run-of-the-river dam in the northwest United States.

Construction began in June 1961, and the main structure and three generators were completed 56 years ago in 1969, with an additional three generators finished in 1981.

Built and operated by the U.S. Army Corps of Engineers, Lower Monumental Dam is part of the Columbia River Basin system of dams.

Behind the dam, Lake Herbert G. West is the reservoir; it extends 28 miles (45 km) east to the base of Little Goose Dam.

Lake Sacajawea, formed from Ice Harbor Dam, runs 22 miles (35 km) southwest, downstream from the base of the dam.

Columbia River Basin
Columbia River Basin
Lower Monumental Dam with the lock in the center of the river (far side in photo), the power generation on the northwest side of the river, and spillway in the middle of the dam, between the powerhouse and the lock.