Lake Ontario and the St. Lawrence River

The north shore of Lake Ontario is richly diverse and scenic.

At the eastern end of the Great Lakes lies Lake Ontario, the smallest of the Great Lakes. Water flows into Lake Ontario from Lake Erie through the Niagara River, and out again to the St. Lawrence River—one of the longest rivers in the world.

The St. Lawrence River begins in eastern Ontario’s Thousand Islands and flows nearly 1,200 kilometres to the Atlantic Ocean. Its waters flow through the St. Lawrence Seaway, a world-class river transportation system that connects inland cities, like Thunder Bay on Lake Superior, with the Gulf of St. Lawrence and the Atlantic Ocean.

More than 8 million people live within the Lake Ontario and St. Lawrence River basins.  Ontario’s major industrial and urban centres, including Toronto, Mississauga and Hamilton, are concentrated along Lake Ontario’s northwest shore in an area called the Golden Horseshoe. This is one of the fastest growing regions in Canada. Other communities along Lake Ontario’s shores include Oakville, Cobourg, Brighton, Kingston, and Cornwall on the St. Lawrence River.

The western and central parts of Lake Ontario support a significant sports fishery, for stocked salmon and trout. The Bay of Quinte region of the lake is also particularly well-known for its excellent walleye and bass fishery. The eastern basin of the Lake supports warm and cool-water fish species, including bass, northern pike, panfish and muskellunge.

At the lake’s east end is a commercial fishery that provides more than a dozen species of warm and cold-water fish, including sunfish, crappie, bullhead, white perch and lake whitefish, primarily for U.S. markets.

Since Lake Ontario is downstream from the other Great Lakes, it receives contaminants and waste from all the industry, farming and other human activity going on throughout the entire Great Lakes area. So it’s no surprise that the Lake Ontario ecosystem has changed dramatically over the past two centuries. 

Fortunately, bans on the release of toxic chemicals into Lake Ontario have helped to improve conditions. Several native wildlife species, such as the bald eagle and osprey, have made spectacular comebacks. But many others are still struggling. Lake Ontario’s fish communities, for example, are suffering from the introduction into the Great Lakes of aquatic invading species, such as the zebra mussel and the round goby. That’s why fishery management projects around Lake Ontario are beginning to focus on restoring native species of fish, including the lake trout, deepwater ciscoe, Atlantic salmon and American eel.