Great Lakes

The Great Lakes are a chain of five interconnected freshwater lakes, Superior, Michigan, Huron, Erie and Ontario, straddling the border between Canada and the United States, together forming the largest group of freshwater lakes on Earth by surface area and holding more than twenty percent of the world's surface fresh water by volume. Covering roughly 94,250 square miles and draining to the Atlantic Ocean through the Saint Lawrence River, the lakes formed about 14,000 years ago as retreating glacial ice sheets carved basins that filled with meltwater; Michigan and Huron are hydrologically a single lake joined at the Straits of Mackinac despite being counted separately. Their rolling waves, strong currents, great depths and distant horizons have earned them the nickname inland seas, and they hold roughly 35,000 islands, including Manitoulin Island, the largest freshwater island in the world. The lakes support extensive aquatic habitat and historically sustained large commercial fisheries, though urbanization, agriculture and industrial development around cities such as Chicago, Detroit, Cleveland and Toronto have significantly reshaped their surrounding ecology and water quality.