The only Great Lake lying entirely inside one country
Lake Michigan holds about 1,180 cubic miles of water and plunges to 923 feet, ranking second among the Great Lakes by volume and depth after Superior. Alone among the five, it sits wholly in the United States across Wisconsin, Illinois, Indiana, and Michigan.
Surface area near 22,300 square miles places it third after Superior and Huron. It measures 307 miles long and 118 wide, with 1,640 miles of shoreline and an average depth of about 279 feet. Through the Straits of Mackinac it shares a water plane with Huron, so hydrologists often treat Michigan–Huron as one lake—the world’s largest freshwater surface. The deepest trough, the Chippewa Basin in the north, is named after a prehistoric lake and is divided from the South Chippewa Basin by the shallower Mid Lake Plateau.
Beneath the surface the Milwaukee Reef runs from between Milwaukee and Racine across to between Grand Haven and Muskegon, splitting the lake into two basins that each circulate clockwise. Westerly winds push warm surface water east, so summer water off Michigan runs 5 to 10 °F warmer than off Wisconsin and softens western Michigan’s climate. The scientist J. Val Klump became the first person to reach the deepest floor, by submersible, in 1985, and a 2018 Purdue report found surface temperatures climbing every decade since 1980.
Hopewell cultures thrived around its basin before Late Woodland peoples; seventeenth-century French forts such as Michilimackinac (1715) later controlled the fur corridor. From the late seventeenth century the lake became a link in a chain of waterways from the Saint Lawrence to the Mississippi, and French voyageurs founded trading posts such as Green Bay.
Chicago, Milwaukee, Green Bay, and Gary grew on its southern and western arcs, turning a glacial basin into an industrial freshwater highway. Before the Civil War about 90 percent of the grain leaving Chicago went east by ship across the lake, and even after railways spread the share seldom fell below half. Beaver Island, at 55.8 square miles, is the largest of its islands.
Source: Lake Michigan
