St. Marys River (Michigan–Ontario) St. Marys River (Michigan–Ontario) The St. Marys River (), sometimes written as the St. Mary's River, drains Lake Superior, starting at the end of Whitefish Bay and flowing southeast into Lake Huron, with a fall of . For its entire length it is an international border, separating Michigan in the United States from Ontario, Canada. The twin cities of Sault Ste. Marie, Ontario, and Sault Ste. Marie, Michigan are connected across the St. Marys River by the Sault Ste. Marie International Bridge. The St. Marys Rapids are just below the river's exit from Lake Superior and can be bypassed by
Sault Ste. Marie, Michigan from in January to in July. On average, only two out of every five years reaches , while there are 85.5 days annually where the high remains at or below freezing and 26.5 nights with a low of or colder. Average monthly precipitation is lowest in February, and highest in September and October. This autumn maximum in precipitation, unusual for humid continental climates, owes to this area's Great Lakes location. From May through July (usually the year's wettest months in most of the upper Midwestern United States, away from large bodies of water), the lake waters surrounding Sault Ste. Marie