Lake Kampeska is a 4,817-acre lake located entirely within the city limits of Watertown. The Big Sioux River is the inlet/outlet to the lake. The Lake Kampeska watershed encompasses 212,707 acres of the Big Sioux River drainage basin. Because the natural outlet from the lake was blocked in the 1940s, the Big Sioux River now acts as the only outlet from the lake.
Camping, fishing, boating and swimming are enjoyed at Sandy Shore Recreation Area on its shores.