There are technically only four (not five) Great Lakes.

Anyone familiar with the Great Lakes can tell you there are five of them: Superior, Michigan, Huron, Erie, and Ontario. But actually, there aren’t, quite. Lakes Michigan and Huron are technically one body of water, as the Straits of Mackinac connect them to form a single hydrologic system. At 3.5 miles wide and just 295 feet deep at its deepest point, the waterway is easy to miss on a map when studying the whole system of Great Lakes. The lakes span a total of 94,250 square miles across eight U.S. states (Illinois, Indiana, Michigan, Minnesota, New York, Ohio, Pennsylvania, and Wisconsin), plus Ontario, Canada.

When taken together, Lake Michigan-Huron is the world’s largest freshwater lake by area. Even the smallest Great Lake, Ontario, is still the 13th-largest lake in the world. More than 90% of America’s surface fresh water is found in the Great Lakes, which are the primary water source for some 40 million people as well as the largest freshwater system in the world.