Lake is a body of fresh or salt water of considerable size, surrounded by land. Lakes generally
form in depressions, such as those created by glacial or volcanic action; they may also form when a section of a river becomes dammed or when a channel is isolated by a change in a river's course. The most lakes are of fresh water, and most lie in the Northern Hemisphere at higher latitudes. More than 60 percent of the world's lakes are in Canada and this is because of the deranged drainage system that dominates the country.
                    Lakes were formed many thousands of years ago by glaciers. At that time, huge glaciers covered the earth. When the glaciers melted, some of the water that was over hollows in the earth became
lakes. Other ways lakes were formed include manmade lakes, natural dams and craters formed in great volcanic explosions. Lakes get bigger and smaller, depending on many factors. Lakes get smaller if they get filled up with silt or other material. They also dry up if they are not replenished with water through rainfall. Other lakes get deeper and bigger as rivers, rainfall and underground water make the lake expand.
                    Lakes can be also categorized on the basis of their richness in nutrients, which typically affect
plant growth. Nutrient-poor lakes are said to be oligotrophic and are generally clear, having a low concentration of plant life. Mesotrophic lakes have good clarity and an average level of nutrients. Eutrophic lakes are enriched with nutrients, resulting in good plant growth and possible algal blooms. Hypertrophic lakes are bodies of water that have been excessively enriched with nutrients. These lakes typically have poor clarity and are subject to devastating algal blooms.
Lake Baikal


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