Lake Ontario

Lake Ontario is the easternmost of the North American Great Lakes, straddling the Canada-United States border between Ontario and New York State. It is the smallest by surface area among the five Great Lakes, covering roughly 19,000 square kilometers.

The lake offers urban waterfronts, harbors and beaches as well as islands and shipping lanes; recreational boating and commercial shipping are both important. Depths reach over 240 meters in places, and the lake is navigable to the St. Lawrence Seaway.

Formed by glacial action at the end of the last Ice Age, the lake has supported indigenous communities and later European settlement, military activity and trade. Cities and ports developed on its shores through the 18th to 20th centuries as part of continental transport networks.

Lake Ontario lies between the Canadian province of Ontario to the north and the U.S. state of New York to the south, with the St. Lawrence River flowing out from its eastern end toward the Atlantic.

• Outflow to St. Lawrence River: Water from Lake Ontario flows into the St. Lawrence River, forming the outflow of the Great Lakes system toward the Atlantic Ocean.
• Major shoreline cities: Toronto and Rochester are among the larger cities on its shores, with port facilities and waterfront parks.