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Parks Canada - Lake Ontario

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Canada’s National Marine Conservation Areas System Plan

Lake Ontario

The Water

Lake Ontario is the smallest of the Great Lakes, with a surface area of only 18,960 km², although it has a greater volume than Lake Erie. Maximum depth is 244 m, with an average depth of 86 m. The main portion of the lake is a smooth east-west trough divided into three basins. Water depths descend gradually towards these basins. Depths of less than 20 m occur in a 3-7 km wide band along the coast, representing only 10% of the lake. The eastern part of the lake is less than 50 m deep throughout, with a complex bottom relief. Upwelling occurs along the western edge of the lake and prevents stratification in this part of the lake. Surface water temperatures range from 0°-4°C in January and 12°-20°C in July. Primary productivity is moderate, about half that of Lake Erie. Water clarity is usually in the 5-10 m range, while the lake's retention time is about six years. Lake Ontario has the least amount of ice cover of any of the Great Lakes, with over 85% of the lake surface normally ice free during the winter.

The Coast

Along the eastern half of the lake the shoreline is rocky, irregular and low-lying, with wide flat-rock platforms, bays, coves and channels. The western half is dominated by a relatively straight shoreline of low eroding bluffs subject to high rates of erosion, ranging from 0.3-3 m/yr. These bluffs are generally 3-10 m in height, but are up to 100 m high in the area of the Scarborough Bluffs. Wind-blown shore sediment has created several barrier beaches, sand dunes and sand spits. Small wetlands occur locally.

The Wildlife

Some 85 fish species have been recorded in Lake Ontario. A number of once common species are now no longer found in the lake, including the deepwater sculpin (once so numerous they were considered a nuisance), blue walleye, bridle shiner, kiyi and blackfin cisco. Though still present, lake trout and lake whitefish are no longer very common. At present the most abundant native species include yellow and brown bullhead, American eel, northern pike, yellow perch, walleye, sauger, smallmouth and largemouth bass. Various species of amphibians and reptiles are common in wetland areas. Although ring-billed gulls dominate the water bird fauna of this region by a wide margin, there are also small colonies of herring gulls, double-crested cormorants, Caspian and and common terns, great blue herons and black-crowned night herons. Significant numbers of waterfowl -- Canada geese, black ducks, mallards, canvasbacks, redheads and scaups -- stage in the region both in spring and fall. Numerous birds winter where open water permits, mainly gulls and various ducks.


This region is not yet represented in the national marine conservation areas system. Two representative marine areas have been identified: Prince Edward Point and Wellers Bay. The Prince Edward Point area was subsequently selected as the preferred area for consideration as a possible national marine conservation area. Preliminary discussions with the province of Ontario and local groups is the next step. (For details on the establishment process, see The NMCA Program.)

Last Updated: 2013-05-10 To the top
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