Duluth, Minnesota at the western end of the Saint Lawrence Seaway, the Duluth–Superior seaport is the largest and farthest-inland freshwater seaport in North America. By far the largest and busiest on the Great Lakes, the port handles an average of 46 million short tons of cargo and over 1,100 visits each year from domestic and international vessels. With of waterfront, it is one of the leading bulk cargo ports in North America and ranks among the top 20 ports in the United States. Duluth is a major shipping port for taconite pellets, made from concentrated low-grade iron ore and destined for midwestern
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.