The Detroit River flows for 24nmi from Lake St. Clair to Lake Erie as a strait in the Great Lakes system and forms part of the border between Canada and the United States. The river divides the metropolitan areas of Detroit, Michigan and Windsor, Ontario - an area referred to as Detroit–Windsor. The two cities are connected by the Ambassador Bridge, the Detroit–Windsor Tunnel and the Michigan Central Railway Tunnel.The river's name comes from the French Rivière Détroit, meaning River of the Strait. The Detroit River has served an important role in the history of Detroit and is one of the busiest waterways in the world. The river travels west and south from Lake St. Clair to Lake Erie, and the whole river is coterminous with the border between Canada and the United States.The river serves as an important transportation route connecting Lake Michigan, Lake Huron, and Lake Superior to the St. Lawrence Seaway and Erie Canal. When Detroit underwent rapid industrialization at the turn of the 20th century, the Detroit River became notoriously polluted and toxic. In recent years, however, the ecological importance of the river has warranted a vast restoration effort, and the river today has a wide variety of economical and recreational uses. There are numerous islands in the Detroit River, and much of the lower portion of the river is incorporated into 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 an American Heritage River and a Canadian Heritage River — the only river to have this dual designation.