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
Duluth Ship Canal of adverse weather. Around a thousand vessels a year ship from the Duluth–Superior port. The construction of the first locks on the St. Marys River in 1855 allowed for navigation between the lakes, and Superior Bay presented itself as an attractive harbor. From the point of view of Duluth residents, however, arrangements were less than satisfactory, as ships from that city had to pass Superior, Wisconsin on the way to the lake, as the only natural outlet was between Minnesota Point and Wisconsin Point at the far end of the bay. Also, while sheltered, the bay was not naturally as