The base of an island fans out beneath the surface of Lake Superior in Ontario.

Lake Ontario is 19 000 km2 (10 000 km2 in Canada), with a drainage area of 90 130 km2, an elevation of 74 m, a mean depth of 86 m (max 244 m), length 311 km and width 85 km. It is the smallest in surface area and most easterly of the GREAT LAKES and eighth-largest body of fresh water in North America. 

The lake receives most of its water supply from the other Great Lakes through the NIAGARA RIVER and discharges into the ST LAWRENCE RIVER through the Kingston Basin at its northeast end. Other tributaries are the Genesee, Oswego and Black rivers in New York state and the Trent River in Ontario.

The clockwise tour of geological features around Lake Superior, the world's largest freshwater lake . The lake has an area of 82,380 km2. It was part of the Mississippi drainage until the Pleistocene, and formed part of glacial lake Algonquin.

 The modern lake surface is 183 m above sea level, while the deepest point (406 m water depth) is 223 m below mean sea level! Starting at the Algoma district, the tour proceeds around the rocky shores of Ontario, also examining features in the hinterland to the immediate north of the lake. From the city of Thunder Bay, the tour proceeds to Duluth, Minnesota, and then east through Wisconsin to the Upper Peninsula of northern Michigan, U.S.A.

Lake Ontario occupies a bedrock depression originally produced by stream erosion and later modified by glaciation. Several glacial lakes of varying elevation occupied the basin before the current level and outlet were established about 11 000 years ago. 

The present basin has an elliptical plan with an east-west orientation and a complex lake bed reflecting its underlying rock structure and the effects of glaciation. The lakeshore is typically a low bluff of rock or glacial sediment with a narrow beach.

The intersection of older and higher glacial and lake deposits at the southeast end of TORONTO has produced the Scarborough Bluffs - spectacular, cathedral- like cliffs rising as high as 100 m above the lake. Other scenic shore features include the rocky coasts and islands of the Kingston Basin and the extensive sandy beaches at HAMILTON and Toronto on the Canadian side and Mexico Bay in the US.