ALGONQUIN, LAKE

large glacial lake that once existed in North America and covered most of the area now occupied by the Great Lakes of Superior, Michigan, and Huron. It was present in the Pleistocene Epoch (1,600,000 to 10,000 years ago), a geologic glacial period when the ice field (called the Laurentide Ice Sheet) was retreating northward from the Great Lakes region. The body of water, perhaps 100,000 square miles (250,000 square km) in area and with depths of up to 1,500 feet (460 m), at various stages drained through channels that included the Trent Valley and the Mattawa, Ottawa, St. Clair, and Mississippi rivers. Remnants of the lake include Lakes Superior, Michigan, Huron, Nipigon, Simcoe, and Nipissing.