Lake Ontario, bounded on the north by Ontario and on the south by Ontario's Niagara Peninsula and by New York State, is one of the five Great Lakes of North America.

The name of the lake is an Iroquois word meaning either "beutiful lake" or "sparkling water". The Canadian province of Ontario was later named after the lake.

Lake Ontario is the eastern-most and smallest in surface area (19,009 square kilometers) of the Great Lakes. It exceeds only Lake Erie in volume (1639 km³). Its primary inlet is Niagara Falls (from Lake Erie) and primary outlet is the Saint Lawrence River. Other rivers such as the Trent River and the Oswego River also flow into it. Other notable geographic features are Hamilton Harbour, the Bay of Quinte, and the Toronto Islands.

The lake was carved out by glaciers and its bottom is rocky. The lake rarely freezes in winter.

A portion of the Great Lakes Waterway passes through the lake, which is accessible from upstream by the Welland Canal and from downstream by the Saint Lawrence Seaway. The Trent-Severn Waterway for pleasure boats connects Lake Ontario to Georgian Bay of Lake Huron through Lake Simcoe. The Rideau Waterway, also for pleasure boats, connects Lake Ontario at Kingston to the Ottawa River at Ottawa.

The lake was a border between the Huron and their vassals and the Iroqouis Confederacy in pre-Eruopean times. The first westerner to reach the lake was Étienne Brulé in 1615.

Today the American shore of the lake is largely rural, with the exception of Rochester, New York. A large conurbation called the Golden Horseshoe (including Toronto and Hamilton, Ontario) is to be found on the Canadian side. The excellent farmland on the northern shore of the lake has lead it to be a havily populated area. Today about a quarter of Canada's population lives near the shores of Lake Ontario.

Great Lakes
Lake Superior Lake Michigan Lake Huron Lake Erie Lake Ontario