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
Lake Superior National Estuarine Research Reserve freshwater estuaries. One of these estuaries formed where the waters of the St. Louis River enter Lake Superior. Lake Superior, which is bordered by Michigan, Minnesota, Wisconsin and Ontario, Canada, is the largest of the Great Lakes and the most pristine. Freshwater estuaries occur where rivers and Great Lakes water mix in shallow wetlands located near the mouth of a river. The Reserve contains all three common defining characteristics of a Great Lakes freshwater estuary including a) presence of a drowned river mouth b) adequate zone of transition between lake and river water and c) influence from tide or seiche.