What happens to a lake over time?

The middle layer, the thermocline, mixes and turns over throughout the year. It turns over due to climate, nutrient variations, and geologic activity such as earthquakes. However, major lake turnover happens during the fall and spring, when the lake's cold and warm waters mix and readjust.



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Oxygen from the surface mixes with the bottom, while nutrients trapped near the bottom are free to mix throughout the lake. This is why, sometimes, in the spring and fall the lake can smell unpleasant. Decomposing organic materials are churned up from the bottom of the lake, bringing a signature sign of lake turnover.

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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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After several thousand more years, your lake will continue become shallower in the center, more shoreline will erode into the water, trees will fall in, leaves, dust and dirt will blow in, weeds will become thicker and grow out farther into the lake, die, decay and add to the bottom.

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A lake has turned over when water temperatures are the same from the surface to the bottom. The process can take days or even months to complete, depending on lake shape and depth, and air and water temperatures.

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Cooler weather means your lake or pond will soon turn over. When this happens the entire water column will mix or “turnover”. As a result, the bottom sediments are stirred and anaerobic conditions are mixed throughout the entire pond for a period of time.

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Turnover is like being at the mall … or at a fair. 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.

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Algae are tiny plants that multiply rapidly when the water becomes stagnant. Some types of algae produce toxins that can be harmful to both humans and animals. Moreover, these algae can form dense layers that block sunlight from reaching the bottom of the water.

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Lakes lifespans are limited, as rivers dump their sediment into them and dead plant material builds up on the lake bottom. Most lakes are less than 10,000 years old.

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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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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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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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Most lakes and ponds don't completely freeze because the ice (and eventually snow) on the surface acts to insulate the water below. Our winters aren't long or cold enough to completely freeze most local water bodies. This process of lakes turning over is crtically important to the life in the lake.

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