One of the major features of Toronto is that it sits on Lake Ontario. Toronto derives some major economic activity on the waterfront. The lake is one of the five Great Lakes of North America. It's the smallest of the Great Lakes and the only one that does not border with the US state of Michigan.

About one-quarter of the population of Canada lives in southern Ontario near Lake Ontario.

Some major cities on Lake Ontario include

Lake Ontario has an elevation of 246 feet (75 m) above sea level. Its length is 193 miles (311 km), and its width is 53 miles (85 km). The average depth is 283 feet (86 m), with a maximum depth of 802 feet (244 m).

Lake Ontario's primary inlet is the Niagara River (from Lake Erie) and primary outlet is the St. Lawrence River. Other major rivers which flow into it include the Don River; Humber River; Trent River; the Cataraqui River; the Genesee River; the Oswego River; the Black River; and the Salmon River.

Other geographic features include Hamilton Harbour, the Bay of Quinte, the Toronto Islands, and the Thousand Islands. The Bay of Quinte separates most of Prince Edward County from the north shore except for a 3km stretch of land connecting it to the mainland. The largest island on the lake is Wolfe Island located near Kingston at the St Lawrence River entrance. It is accessible by ferry from both Canada and the U.S.