River, southeastern Michigan, U.S. Forming part of the boundary between Michigan and Ontario, Can. , it connects Lake St. Clair with Lake Erie. It flows south for 32 mi (51 km) past Detroit and Windsor, Ont., where a bridge and tunnel connect the two cities. The largest islands in the river are Belle Isle (a city park of Detroit) and Grosse Ile (a residential area with an airport), both in Michigan, and Fighting Island in Ontario. The river is heavily used by both pleasure craft and Great Lakes shipping