Great Lakes Waterway River between Huron and Erie. Usually, one or more U.S. Coast Guard icebreakers help keep the water passage open for part of the fall and early winter, although shipping usually ceases for two to three months thereafter. The Great Lakes Waterway is co-administered by the governments of Canada and the United States of America. The waterway allows passage from the Atlantic Ocean to the inland port of Duluth on Lake Superior, a distance of and to Chicago, on Lake Michigan, at . Together with the Saint Lawrence Seaway, the Waterway allows both ocean-going vessels and the ore, grain and coal-bearing
Glacial history of Minnesota present Lake Superior. Its shorelines stood nearly 148 meters above the level of its modern successor, Lake Superior. During its early history Lake Duluth drained into the Mississippi River down the St. Croix River Valley. There were two outlets, one along the Kettle and Nemadji Rivers in Minnesota and another to the east along the Bois Brule River in Wisconsin. Later, however, when the Superior lobe had retreated farther to the northeast, the waters of Lake Duluth merged those in the Michigan and Huron basins, and the southern outlets were abandoned in favor of a lower one on the east