Superior, Lake, one of the five Great Lakes of North America and the largest freshwater lake in the world. The lake is shared by Canada and the United States. On the north is the province of Ontario and on the United States side are Minnesota, Wisconsin, and Michigan. From east to west, the lake is 383 miles (616 km) long; north-south, it measures a maximum of 160 miles (257 km). About one-third of the total area of 31,700 square miles (82,100 km 2) is Canadian.
The surface of Lake Superior is the highest of all the Great Lakes, lying 600 feet (183 m) above sea level. The lake is also the deepest of the five, reaching a depth of 1,332 feet (406 m) in the southeast. Much of the central part of the lake exceeds 500 feet (150 m) in depth. The waters of the lake are clear and cold, seldom warming much even in summer. Despite the area's severe winters, however, the lake rarely freezes over. Its shores, though, are locked in ice for several months each year. Islands are numerous. Largest is Isle Royale, a United States national park. Other islands include St. Ignace and Michipicoten in Ontario, and the Apostle Islands of Wisconsin.
The drainage basin supplying the lake is relatively small and tributary rivers are short. Except for the St. Louis River, which enters the lake at Duluth, the larger streams feeding the lake are all in Ontario. The St. Marys River is the outlet for Lake Superior, linking it with Lake Huron.
Lake Superior is part of the vast inland waterway known as the Great Lakes–St. Lawrence Seaway system. For eight months of the year, freighters move across the lake, carrying iron ore, grain, lumber, and newsprint from such ports as Thunder Bay and Duluth-Superior. Passing through the St. Marys River and the Sault Ste. Marie Canals, vessels have access to the other Great Lakes and, by way of the St. Lawrence Seaway, the Atlantic Ocean.
Étienne Brulé is thought to have been the first European to reach Lake Superior, in 1623. Further explorations were made by the Jesuit Claude Allouez, Sieur Duluth, and other missionaries and fur traders. The French called the lake Lac Supérieur (Upper Lake), to distinguish it from the lower Great Lakes. As mining and lumbering developed around the lake in the 19th century, cities and towns grew up along its shores. With the opening of the first ship canal at Sault Ste. Marie in 1855, the lake was well on its way to becoming a vital transport link to the heart of America. In the 20th century, as pollution became a major concern, Lake Superior remained perhaps the least polluted of the Great Lakes.