Lake Ontario
Geography

Lake Ontario is the easternmost of the Great Lakes and the smallest in surface area (7,340 sq mi, 19,000 km), although it exceeds Lake Erie in volume (393 cu mi, 1,640 km). It is the 13th largest lake in the world. When its islands are included, the lake's shoreline is 712 miles (1,146 km) long. As the last lake in the Great Lakes' hydrologic chain, Lake Ontario has the lowest mean surface elevation of the lakes at 243 feet (74 m) above sea level; 326 feet (99 m) lower than its neighbor upstream. Its maximum length is 193 statute miles (311 kilometres; 168 nautical miles), and its maximum width is 53 statute miles (85 km; 46 nmi). The lake's average depth is 47 fathoms 1 foot (283 ft; 86 m), with a maximum depth of 133 fathoms 4 feet (802 ft; 244 m). The lake's primary source is the Niagara River, draining Lake Erie, with the Saint Lawrence River serving as the outlet. The drainage basin covers 24,720 square miles (64,030 km). As with all the Great Lakes, water levels change both within the year (owing to seasonal changes in water input) and among years (owing to longer-term trends in precipitation). These water level fluctuations are an integral part of lake ecology and produce and maintain extensive wetlands. The lake also has an important freshwater fishery, although it has been negatively affected by factors including overfishing, water pollution and invasive species.

Baymouth bars built by prevailing winds and currents have created a significant number of lagoons and sheltered harbors, mostly near (but not limited to) Prince Edward County, Ontario, and the easternmost shores. Perhaps the best-known example is Toronto Bay, chosen as the site of the Upper Canada capital for its strategic harbor. Other prominent examples include Hamilton Harbour, Irondequoit Bay, Presqu'ile Bay, and Sodus Bay. The bars themselves are the sites of long beaches, such as Sandbanks Provincial Park and Sandy Island Beach State Park. These sand bars are often associated with large wetlands, which support large numbers of plant and animal species, as well as providing important rest areas for migratory birds. Presqu'ile, on the north shore of Lake Ontario, is particularly significant in this regard. One unique feature of the lake is the Z-shaped Bay of Quinte which separates Prince Edward County from the Ontario mainland, save for a 2-mile (3.2 km) isthmus near Trenton; this feature also supports many wetlands and aquatic plants, as well as associated fisheries.

Major rivers draining into Lake Ontario include the Niagara River, Don River, Humber River, Rouge River, Trent River, Cataraqui River, Genesee River, Oswego River, Black River, Little Salmon River, and the Salmon River.
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