Lower Monumental Lock and Dam is a hydroelectric, concrete, run-of-the-river dam in the northwest United States. Located on the lower Snake River in southeast Washington, it bridges Franklin and Walla Walla counties; it is south of Kahlotus and north of Walla Walla. Construction began in June 1961, and the main structure and three generators were completed in 1969, with an additional three generators finished in 1981. Generating capacity is 810 megawatts, with an overload capacity of 932 MW. The spillway has eight gates and is in length. 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 east to the base of Little Goose Dam. Lake Sacajawea, formed from Ice Harbor Dam, runs southwest, downstream from the base of the dam. Navigation lock Single-lift Width: Length: See also List of dams in the Columbia River watershed Lower Granite Dam Little Goose Dam Ice Harbor Dam References External links Lower Monumental Lock & Dam @ US Army Corps of Engineers Dams in Washington (state) Dams on the Snake River Gravity dams Hydroelectric power plants in Washington (state) Run-of-the-river power stations Buildings and structures in Franklin County, Washington Buildings and structures in Walla Walla County, Washington Dams completed in 1969 1969 establishments in Washington (state) Energy infrastructure completed in 1969 Energy infrastructure completed in 1981 United States Army Corps of Engineers dams