Duluth, Minnesota Lakes Waterway and the Saint Lawrence Seaway. Duluth forms a metropolitan area with neighboring Superior, Wisconsin, called the Twin Ports. The cities share the Duluth–Superior harbor and together are the Great Lakes' largest port, transporting coal, iron ore (taconite), and grain. A tourist destination for the Midwest, Duluth features the United States' only all-freshwater aquarium, the Great Lakes Aquarium; the Aerial Lift Bridge, which spans the Duluth Ship Canal into the Duluth–Superior Harbor; and Minnesota Point (known locally as Park Point), the world's longest freshwater baymouth bar, spanning . The city is also the starting point for vehicle trips along
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