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.
The river's English name comes from the French Rivière du Détroit (translated as "River of the Strait"). The Detroit River has served an important role in the history of Detroit and Windsor, and is one of the world's busiest waterways. It is an important transportation route connecting Lake Michigan, Lake Huron, and Lake Superior to Lake Erie and eventually to Lake Ontario, the St. Lawrence Seaway and the Erie Canal. When Detroit underwent rapid industrialization at the turn of the 20th century, the Detroit River became notoriously polluted and toxic. Since the late 20th century, however, a vast restoration effort has been undertaken because of the river's ecological importance.
In the early 21st century, the river today has a wide variety of economic and recreational uses. There are numerous islands in the Detroit River, and much of the lower portion of the river is part of the Detroit River International Wildlife Refuge. The portion of the river in the city of Detroit has been organized into the Detroit International Riverfront and the William G. Milliken State Park and Harbor. The Detroit River is designated both an American Heritage River and a Canadian Heritage River—the only river to have this dual designation.