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Freshwater aquatic ecosystems in Canada
Canada contains an abundance of freshwater ecosystems, including lakes, ponds, rivers, streams, prairie potholes, and wetlands.
A lake is a sizable water body surrounded by land and fed by rivers, springs, or local precipitation. The broad geographical distribution of lakes across Canada is primarily the result of extensive glaciation in the past.
Lakes can be classified on the basis of a variety of features, including their formation and their chemical or biological condition. One such classification identifies two types of lakes: oligotrophic and eutrophic. Oligotrophic lakes are characterized by relatively low productivity and are dominated by cold-water bottom fish such as lake trout. Eutrophic lakes, which are shallower, are more productive and are dominated by warm-water fish such as bass. Great Slave Lake (Northwest Territories) and most prairie lakes represent the two types, respectively.
Ponds are smaller bodies of still water located in natural hollows, such as limestone sinks, or that result from the building of dams, either by humans or beavers. Ponds are found in most regions and may exist either seasonally or persist from year to year.
Rivers and streams are bodies of fresh, flowing water. The water runs permanently or seasonally within a natural channel into another body of water such as a lake, sea, or ocean. Rivers and streams are generally more oxygenated than lakes or ponds, and they tend to contain organisms that are adapted to the swiftly moving waters (e.g., black fly larva and darter fish). Some of the larger rivers in Canada include the St. Lawrence, Mackenzie, Fraser, Athabasca, North and South Saskatchewan, and Saint John rivers.
Some rivers flow into oceans, the great saltwater bodies that cover 70% of the earth's surface. The tidal areas where saltwater and fresh water meet are called estuaries. These productive ecosystems, found on Canada's coasts, contain unique assemblages of organisms, including starfish and sea anemones.
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