Winter kill is a dreaded term in lake management used to describe a massive toll on the fish population of a lake due to ice cover. One of the best ways to prevent winter kill is to prepare for winter by removing and/or moving any lake aerators.
The Science of Lake Maintenance
Having multiple aerators running during the winter months is a bad idea. You do not want to mix the water too much during the freezing months. Why? The explanation has to do with the unique behavior of water as it cools.
Water becomes denser as it cools until it reaches 4°C (39.2°F). Below 4°C, the water molecules begin forming more loose clusters, which means that it begins to become less dense as it starts to reach freezing temperatures. That’s why ice floats on the surface of a lake, and that’s why in winter, the coldest water is at the top of the basin.
Removing surface aerators prevents the machinery from being damaged by the cold, and sub surface aerators being moved closer to the surface prevents the top layer of water from circulating and cooling the deeper, warmer waters.
Stored or Added Oxygen?
Winter kill occurs when the total amount of stored and added oxygen is lower than the total amount of consumed oxygen. Whether or not your lake’s residents will have enough oxygen is dependent upon the size of the lake as well as the population size.
If you are a lake management professional, the safest way of ensuring your fish and plants have enough oxygen is to leave one sub surface air diffuser that is not focused on circulating the water, but on introducing small bubbles of oxygen into the water to keep an opening in the ice on the surface of the water. If you move the aerator from the center to the side of the lake, the circulation is even more contained.
Adding oxygen by means of a sub surface air diffuser allows you to keep fish and plants oxygenated without cooling the water too much due to circulation.