Great Lakes form a single, naturally interconnected body of fresh water, within the Great Lakes Basin. They form a chain connecting the east-central interior of North America to the Atlantic Ocean. From the interior to the outlet at the Saint Lawrence River, water flows from Superior to Huron and Michigan, southward to Erie, and finally northward to Lake Ontario. The lakes drain a large watershed via many rivers, and are studded with approximately 35,000 islands. There are also several thousand smaller lakes, often called "inland lakes," within the basin. The surface area of the five primary lakes combined is roughly equal to
Nipissing Great Lakes both Lake Erie and Niagara Falls would lack the volume of water needed to cut the channel through the Niagara limestone cap rock. Lake Erie was a nonglacial lake in this period. The third stage of nonglacial development ended the Lake Algonquin. A fourth stage was initiated when the upper lakes entered the Nipissing Great Lakes stage and that volume of water was diverted through the outlet at North Bay, Ontario. At this low stage, Lake Erie was to lower than present lake level and which lasted throughout the time of the Nipissing Great Lakes. The Lake Algonquin period of