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″N091°18′26″W). The lake is 7,688 acres (31.11 km²) and is shored by the city from which its name came from: Onalaska, Wisconsin.