Lewis and Clark Lake is an impoundment on the Missouri River above Gavins Point Dam, near Yankton, South Dakota. It is located on the border of South Dakota and Nebraska. The reservoir is approximately 25 miles (40 km) long, with a surface area of 31,000 acres (130 km²); it has a maximum depth of 45 feet (14 m). It is the smallest of the Pick-Sloan Plan impoundments, and has been plagued with siltation problems.