Lake Ontario is the only lake among the Great Lakes which does not share its border with Michigan. Its length is about 193.2 mi (311 km). The surface area of Lake Ontario is about 7335.9 sq mi (19,000 sq km). It is the smallest in terms of surface area among the Great Lakes and is the world’s 13th largest lake.

Various rivers and streams flow into Lake Ontario, including the Niagara River, Humber River, Trent River, and Genesee River.