How old are most lakes?

Most of the world's millions of lakes are less than 18,000 years old and were formed when glaciers melted at the end of the last Ice Age. Geologists classify just 30 lakes, including Ohrid and Prespa, as “ancient”—defined by some researchers as persisting more than one ice age cycle (at least 130,000 years).



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The average lifespan of a lake is usually about 10,000 years. What commonly happens is the depression of the lake fills with sediment, water levels go down and wonderful wetlands are created.

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Situated in south-east Siberia, the 3.15-million-ha Lake Baikal is the oldest (25 million years) and deepest (1,700 m) lake in the world. It contains 20% of the world's total unfrozen freshwater reserve.

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Lake aging is the natural process by which a lake fills in over geologic time with erosional materials carried in by tributary streams, with materials deposited directly from the atmosphere, and with materials produced within the lake itself.

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Eutrophication is the natural aging of a lake by biological enrichment of its water. In a young lake the water being cold and clear does not support much life. But with time streams draining into the lake introduce nutrients such as nitrogen and phosphorus which encourage the growth of aquatic organisms.

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In lakes and ponds, much of the species diversity is concentrated in the littoral zone, near the shore, where algae and plants thrive in the abundant light needed for photosynthesis. Living within the plant matter is a cornucopia of animals including snails, amphibians, crustaceans, insects, and fish.

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Turnover is a natural way the lake cleans up harmful bacteria and algae. It carries dead algae down into the depths of the lake where there is less sunlight, helping to prevent algae growth. You can think of it as an escalator, moving the algae cells from the top of the lake to the bottom.

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Solution Lakes: Lakes can form when underground deposits of soluble rocks are dissolved by water running through the area, making a depression in the ground. Rock formations made of sodium chloride (salt), or calcium carbonate (limestone), are most likely to be dissolved by acidic waters.

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Exorheic, or open lakes drain into a river, or other body of water that ultimately drains into the ocean. Endorheic basins fall into the category of endorheic or closed lakes, wherein waters do not drain into the ocean, but are reduced by evaporation, and/or drain into the ground.

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During the summer, if a waterbody is deep enough to stratify into three distinct layers, with one warm layer on top, one cold layer at the bottom and a layer of rapidly changing temperature in between (called a “thermocline”), then it is a “lake,” while a waterbody with one or two weakly defined layers is a “pond.”

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If left alone, the pond or lake will eventually fill in completely, and become a swamp or wetland at best. Most existing farm ponds fall in the eutrophic category and need help quickly to slow the aging process.

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