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What Causes a Lake to Winter Kill such as Loon Lake in 1999/2000?
By November most lakes in our area are throughly mixed from the strong winds that occur in the fall resulting in oxygen being naturally added to the water when the wind and water interface. During December ice and snow form on the lakes sealing the water from the atmosphere thus eliminating oxygen input from outside sources. Aquatic plants such as algae and rooted submergent plants can help produce oxygen during the winter as long as light can penetrate down through the snow and ice. But during winters like this one that start early and have large amounts of snow create conditions that completely eliminate any light penetration to the plants and thus they start to decay. The decompositions of the plants and other organic matter (i.e., leaves, plants, waste from industry, humans, waterfowl or fish) that accumulate on the lake bottom consume oxygen during this period and can create a large enough deficits that a lake can lose all of the oxygen in the water volume causing fish and other aquatic organisms to die. Preventing Winters kill: Winter kills are not something that can be predicted but we can certainly lessen their frequency through use of winter aeration systems. Aeration systems are most suitable on shallow lakes with histories of frequent winter kill events such a Loon Lake and Lake Elysian. Shallow lakes often lack enough water volume to maintain good oxygen concentrations throughout the winter. There are many different varieties of aeration systems and they all have their benefits and drawl backs. The most commonly used system in this area is called a bubbler system. These systems are designed to run a high volume of air at a very low pressure through air line connected to aeration heads place on the lake bottom (i.e., Loon lake). Bubbler aeration systems function by opening up water so that oxygen exchange occurs naturally from aquatic plants and through the wind and water mixing at the surface. These systems also help distribute oxygen by mixing the entire volume of water in the lake. This allows oxygen concentrations to maintain a higher average concentration over the entire volume of the lake restricting or eliminating the oxygen-depleted zone of water near the bottom. An aeration system will not completely rule out the possibility of a winter kill. In fact this winter has tested many of the aeration systems in the area and presently most shallow lakes and ponds without an aeration system have very low oxygen concentrations or possibly have experienced some degree of winter kill.