The St. Clair River, separating Michigan from Ontario, is one of the world's greatest natural waterways. The 40-mile strait connects Lake Huron with Lake St. Clair, northeast of Detroit, as a key link in the Great Lakes chain of mid-North America. Effectively, the St. Clair drains Lakes Superior, Lake Michigan, Lake Huron, and their tributaries, pouring billions of gallons of freshwater into the lower Great Lakes over the Niagara Falls and out through...