The Soo Locks first opened to navigation in 1855. Built at Sault Ste. Marie, Michigan, they enabled vessels to bypass the rapids in the Saint Marys River between Lake Superior and the lower Great Lakes.
Before the locks, boats and cargo had to be unloaded and carried around the rapids. The new canal and lock system created a continuous shipping route, helping Lake Superior’s growing iron and copper industries reach markets farther east. This was a major transportation change in the nineteenth-century Great Lakes region.
The name “Soo” is an English pronunciation of Sault Ste. Marie. The locks are on the U.S. side of the river, while Canada operates a separate smaller canal and lock system nearby. Modern Soo Locks are much larger and more capable than the original works.
The locks are often mentioned alongside the Saint Lawrence Seaway, but they are separate projects. The Soo Locks solve the elevation and rapids problem at Lake Superior’s outlet; the Seaway carries ships from the lower lakes toward the Atlantic.