The Soo Locks (sometimes spelled Sault Locks, but pronounced "soo") are a set of parallel locks which 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 US state of Michigan and the Canadian province of Ontario. They bypass the rapids of the river, where the water falls 21 feet (7 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.(Wikipedia)