Lake Saint Francis (French: lac Saint-François) is a lake which borders southeastern Ontario, southwestern Quebec and northern New York State. It is located on the Saint Lawrence River between Lake Ontario and Montreal, Quebec. The lake forms part of the Saint Lawrence Seaway.

Quick Facts Location, Coordinates ...

Lake Saint Francis
lac Saint-François
View of Lake St. Francis from Highway 2 in South Glengarry, Ontario, near the Quebec border.
Lake Saint Francis
Location	Ontario/Quebec/New York
Coordinates	45°10′N 74°22′W
Type	lake
Primary inflows	Saint Lawrence River
Primary outflows	Saint Lawrence River
Basin countries	Canada, United States
Settlements	Salaberry-de-Valleyfield
Ramsar Wetland
Official name	Lac Saint-François
Designated	27 May 1987
Reference no.	361[1]

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The city of Salaberry-de-Valleyfield is located at the east end of the lake.

Lac Saint-François National Wildlife Area, located on the south shore of the lake, protects wetlands located on the shores of the lake. This area provides important habitat for Redhead ducks and other waterfowl. Thousands of migrating waterfowl stop over in this region. In 1987, it was recognized as a wetland of international significance under the Ramsar Convention.

The Charlottenburgh Marsh, including Cooper Marsh, is an important wetland area located on the north shore of the lake.