Onalaska is a city in La Crosse County, Wisconsin. The population was 14,839 at the 2000 census. The city borders La Crosse directly to the north and three unincorporated rural towns: Onalaska, Medary, and Hamilton. Onalaska is built on a slightly elevated ridge above the Black River. Natural areas include river bottomland as well as high, heavily wooded, scenic bluffs. A manmade reservoir at the city's western edge is known as Lake Onalaska. Onalaska is known as "The Sunfish Capital of the World."