Lake Onalaska is a reservoir located on the Black River and Mississippi River between Wisconsin, and Minnesota. It is approximately 4 miles (6.4 km) across, and is the widest point on the Mississippi River. Located in La Crosse County in the state of Wisconsin, its latitude and longitude are 43°52′01″N 091°18′26″W / 43.86694°N 91.30722°W. The lake is 7,688 acres (31.11 km2) and is shored by the city from which its name came from: Onalaska, Wisconsin. It sits at an altitude of 633 feet (193 m) and is 43 feet (13 m) deep at its deepest.