The St. Louis River is a river in the U.S. states of Minnesota and Wisconsin that flows into Lake Superior. The largest U.S. river to flow into the lake, it is 179 miles (288 kilometers) in length and starts near Hoyt Lakes, Minnesota. The river's watershed is 3634 square miles (9412 km2) in area. Near the Twin Ports of Duluth, Minnesota and Superior, Wisconsin, the river becomes a freshwater estuary.