Lake Ontario drainage basin map

Lake Ontario is the last of the chain of Great Lakes that straddle the Canada/United States border. Its shoreline is bordered by the Province of Ontario on the Canadian side and New York State on the US side. Lake Ontario is the smallest of the Great Lakes, with a surface area of 18 960 square kilometres, but it has the highest ratio of watershed area to lake surface area.

Illustrated map showing Lake Ontario drainage basin
Map: The Lake Ontario Drainage Basin

A map of the Lake Ontario drainage basin, which includes the St. Lawrence River drainage basin. There is a small inset showing the position of Lake Ontario relative to the other Great Lakes as the easternmost lake. The map's scale is in hundreds of kilometres and is oriented northward. It shows the Lake Ontario drainage basin on the left and the St. Lawrence drainage basin on the right.

The Canadian provinces shown are Ontario and Québec. The American state shown is New York. The international border between Canada and the United States runs along the boundary between Ontario and New York, through the middle of Lake Ontario and along the St. Lawrence River. Canadian cities shown (all in Ontario): Cornwall, Kingston, Belleville, Peterborough, Oshawa, Toronto, Hamilton, St. Catharines and Niagara Falls. American cities shown (all in New York): Niagara Falls, Rochester, Auburn, Syracuse, Watertown and Massena.

Also shown on the map are tributaries. Five unnamed tributaries to Lake Ontario are shown, with two along the northern coast of the lake in Ontario, one to the south-west coast in Ontario and two along the south coast in the state of New York.

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2026-07-02