Five Great Lakes hold more than a fifth of Earth’s surface fresh water
Superior, Michigan, Huron, Erie, and Ontario form the largest freshwater lake group by area and the second by volume, storing over 20 percent of the planet’s surface fresh water across 94,250 square miles. Hydrologically Michigan and Huron are already one lake at Mackinac.
Ice sheets gouged the basins, and meltwater filled them about 14,000 years ago. Their combined surface rivals the United Kingdom, and only Lake Michigan lies wholly in the United States. Michigan and Huron meet through the Straits of Mackinac, five miles wide and 120 feet deep, and rise and fall together as one hydrological lake. Superior, Michigan–Huron, and Erie sit at similar heights, while Ontario lies far lower beyond the Niagara Escarpment.
Water leaves Superior by the St. Marys River and the Soo Locks, passes the St. Clair and Detroit rivers into Erie, drops over Niagara into Ontario, and exits by the Saint Lawrence; the Welland Canal lets ships bypass the falls. Canals on the Chicago and Calumet rivers link the basin to the Mississippi and the Gulf of Mexico. Container ships now outgrow the Seaway locks, limiting that trade on the lakes.
Roughly 35,000 islands dot the chain. Manitoulin in Lake Huron is the largest island in any inland water on Earth, followed by Isle Royale in Superior. Saginaw Bay holds the largest contiguous freshwater wetland in the United States, and Lake St. Clair, 17 times smaller than Ontario, is sometimes proposed as a sixth Great Lake.
Geology shows through at the margins. Lake Nipigon fills a failed arm of the rift centred beneath Superior, ringed by igneous sills hundreds of metres high, and Lake Nipissing contains two volcanic pipes formed by a violent, supersonic eruption. Wildlife includes the eastern wolf, an ancient wolf–coyote blend native to the region, and the muskellunge, the largest member of the pike family.
Source: Great Lakes
