The Detroit River flows west and south for 24 nautical miles (44 km; 28 mi) from Lake St. Clair to Lake Erie as a strait in the Great Lakes system. The river divides the metropolitan areas of Detroit, Michigan, and Windsor, Ontario—an area collectively referred to as Detroit–Windsor—and forms part of the border between Canada and the United States. The Ambassador Bridge, the Detroit–Windsor Tunnel, and the Michigan Central Railway Tunnel connect the cities.