Saint Marys River carries the waters of Lake Superior into Lake Huron. The river is about 40 miles (64 kilometers) long and forms part of the boundary between Ontario and Upper Michigan. Islands divide the river into two main channels, and each channel spreads out into several lakelike bays. The St. Marys Rapids, which are near the northern end of the river, fall nearly 20 feet (6 meters) within 1 mile (1.6 kilometers). The Soo canals and locks have been built so ships can bypass the rapids.
The rapids furnish power for industry. A railroad bridge crosses the rapids. The 2-mile (3.2-kilometer) International Bridge carries traffic across the St. Marys River at Sault Ste. Marie.
