Two Sault Sainte Marie Canals (also known as the Soo Canals) connect Lake Huron and Lake Superior along the Saint Mary's River. The river flows between Ontario and Michigan. The canal on the Canadian side has one lock, but the one on the U.S. side has four locks to accommodate the river's rapid drop. The canals are part of the St. Lawrence Seaway and are a major shipping route for iron and copper ore, steel, and lumber. Present canals were built between 1881 and 1919.