The St. Marys River (sometimes spelled as the St. Mary's River) drains Lake Superior, starting at the end of Whitefish Bay and flowing 120 km southeast into Lake Huron. For its entire length it is an international border, separating Michigan in the United States from Ontario, Canada.

The most important area along the river are the rapids and the twin cities of Sault Ste. Marie, Ontario and Sault Ste. Marie, Michigan. The rapids of the St. Mary's (Sault Sainte Marie in French) are just below the river's exit from Lake Superior. Before Europeans arrived, native Americans fished, traded, and maintained a portage around the rapids. The current name was assigned by the first French explorer, Étienne Brûlé in 1621.

Fort St. Joseph was built on the Canadian shore in 1796 to protect a trading post, and ensure continued British control of the area. The fort fulfilled its role in the War of 1812. The first modern lock was completed in May 1855 by Erastus Corning's St. Mary's Falls Ship Canal Company , and is known as the American Lock. Competitive pressure led to the construction of a Canadian Lock in 1895. The locks were made a part of the Great Lakes Waterway system in 1959 known as the Sault locks.

Tributaries of this river include the:

• Garden River
• Bar River

See also

• List of Michigan rivers
• List of Ontario rivers

External links

• Canadian Heritage web site for St. Marys River
• GreatLakes.net Real time Water levels on St. Marys River (with map)