Superior, WI, and Duluth, MN, share the largest and busiest harbor on the Great Lakes. This is the farthest-inland major bulk-cargo port in North America, handling an average of 38 million short tons of cargo and 1,000 vessel visits each year.

Along the inner harbor the commercial docks facilitate the shipping of mainly iron ore (taconite), coal and limestone and cement, grain, salt, petroleum, wood pulp and wind turbine components.