Saint Marys. 1 River, c.175 mi (280 km) long, rising in Okefenokee Swamp, SE Ga., and flowing, with a great southern bend, E to the Atlantic Ocean. It forms part of the Georgia–Florida line. The lower river is dredged for navigation. 2 River, 63 mi (101 km) long, flowing generally SE from Lake Superior to Lake Huron and forming part of the U.S.-Canada line. The cities of Sault Sainte Marie, Mich., and Ontario are on the river. The rapids there are circumvented by the Sault Sainte Marie Canals. The river and canal are frozen for about five months each year.