Garrison Dam is one of six Missouri River Main stem dams operated by the U.S. Army Corps of Engineers, Omaha District. The dam upstream of Garrison Dam is Fort Peck Dam (near Fort Peck, Montana). The dams downstream of Garrison Dam are: Oahe Dam (near Pierre, South Dakota), Big Bend Dam (near Fort Thompson, South Dakota), Fort Randall Dam (near Pickstown, South Dakota), and Gavins Point Dam (near Yankton, South Dakota). These six mainstem dams impound these Missouri River reservoirs with a total combined water storage capacity of approximately and approximately of water surface area.