Gavins Point Dam, South Dakota

The Gavins Point Dam is the southernmost of four dams on the Missouri River as it crosses South Dakota. At this point, the river forms the boundary between South Dakota and Nebraska. The two mile long dam is mostly on the South Dakota side, though the power station is in Nebraska. The earthen dam was completed in the 1950s by the Army Corps of Engineers, which maintains it to this day. The dam forms a reservoir called Lewis and Clark Lake behind it. Turbines in the dam produce up to 132 megawatts of electricity. These dams have tamed the river by turning it into a ribbon of swollen lakes for most of its course through the state. Siltation in the lake has reduced its surface size by at least 30%.