Ontario, Lake

Smallest and easternmost of the Great Lakes, on the US-Canadian border; area 19,200 sq km/7,400 sq mi. Extending for 310 km/194 mi, it has an average width of about 80 km/50 mi, average depth of 86 m/283 ft, and maximum depth of 244 m/800 ft. It is connected to Lake Erie in the southeast by the Welland Ship Canal and the Niagara River, and drains into the St Lawrence River to the northeast. The opening of the St Lawrence Seaway in 1959 made the lake accessible to large ocean-going vessels. Its main port is Toronto, Canada.

Industry is concentrated around the ports: Toronto, Hamilton, Kingston, Port Hope, and Coburg in Canada; Oswego, Sackett's Harbor, and Charlotte in the USA. Market gardens and fruit farms are cultivated on its southern shores.

The Thousand Islands region is located at its eastern end, the largest being Wolf Island.