Sault Ste. Marie International Bridge in the context of Governor of Michigan

The St. Marys River, sometimes written St. Mary's River, drains Lake Superior, starting at the end of Whitefish Bay and flowing 74.5 miles (119.9 km) southeast into Lake Huron, with a fall of 23 feet (7.0 m). For its entire length it is an international border, separating Michigan in the United States from Ontario, Canada.

The twin cities of Sault Ste. Marie, Ontario, and Sault Ste. Marie, Michigan, are connected across the St. Marys River by the Sault Ste. Marie International Bridge. The St. Marys Rapids are just below the river's exit from Lake Superior and can be bypassed by huge freight ships through the man-made Soo Locks and the Sault Ste. Marie Canal.

The Soo Locks (sometimes spelled Sault Locks but pronounced "soo") are a set of parallel locks, operated and maintained by the United States Army Corps of Engineers, Detroit District, that enable ships to travel between Lake Superior and the lower Great Lakes. They are located on the St. Marys River between Lake Superior and Lake Huron, between the Upper Peninsula of the U.S. state of Michigan and the Canadian province of Ontario. They bypass the rapids of the river, where the water falls 21 ft (6.4 m). The locks pass an average of 10,000 ships per year, despite being closed during the winter from January through March, when ice shuts down shipping on the Great Lakes. The winter closure period is used to inspect and maintain the locks.

The locks share a name (usually shortened and anglicized as Soo) with the two cities named Sault Ste. Marie, in Ontario and in Michigan, located on either side of the St. Marys River. The Sault Ste. Marie International Bridge between the United States and Canada permits vehicular traffic to pass over the locks. A railroad bridge crosses the St. Marys River just upstream of the highway bridge.

Sault Ste. Marie (/ˌsuː seɪnt məˈriː/ SOO saynt mə-REE) is a city in the Upper Peninsula of the U.S. state of Michigan. It is the county seat of Chippewa County and is the only city within the county. With a population of 13,337 at the 2020 census, it is the second-most populated city in the Upper Peninsula, behind Marquette. It is the primary city of the Sault Ste. Marie, MI Micropolitan Statistical Area, which encompasses all of Chippewa County and had a population of 36,785 at the 2020 census. Sault Ste. Marie was settled by mostly French colonists in 1668, making it the oldest city in Michigan.

Sault Ste. Marie is located along the St. Marys River, which flows from Lake Superior to Lake Huron and forms part of the United States–Canada border. Across the river is the larger city of Sault Ste. Marie, Ontario; the two cities are connected by the Sault Ste. Marie International Bridge. Between the two cities are the Soo Locks, a set of locks allowing ship travel between Lake Superior and the Lower Great Lakes.