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.

In 1641 Jesuit priests Isaac Jogues and Charles Raymbault ventured the same route as Brûlé, finding many Ojibwe at the rapids, and named it Sault Ste.

Fort St. Joseph was built on the Canadian shore in 1796 to protect a trading post, and ensure continued British control of the area.

During World War II, the Soo Locks and the St. Marys River waterway were heavily guarded by U.S. and Canadian forces coordinated by the U.S. Army's Central Defense Command.

After Pearl Harbor in December 1941, fear of possible air or paratroop attacks by German forces led to a major expansion of defence measures.

Scenarios envisioned included U-boats in Hudson Bay launching attack aircraft, and one-way bombing or paratroop missions along a great circle route from German-occupied Norway.

Canada provided an anti-aircraft battalion, elements of the Royal Canadian Mounted Police, barracks and defensive positions for some of the U.S. force, and a warning system of 266 aircraft observation posts of the Aircraft Identity Corps extending northward to Hudson Bay.

By late 1943, with no threat emerging and spare components stockpiled in the event of lock damage, the U.S. forces were cut to 2,500 troops, and the AA and air warning defences were abandoned.

The United States Army Corps of Engineers owns and operates a hydroelectric generating plant directly north of the American locks.

The American Soo Locks are the major transportation route around the St. Marys Rapids, but the Canadian Sault Ste.

A set of compensating works are located at the mouth of the rapids, which are used to control the outflow of water from Lake Superior.

[9] The berm begins at Gate #1 of the compensating works so as to retain the ability to provide a dedicated flow over the fish spawning habitat, independent of water supply over the rest of the rapids.