Springtime in Michigan tends to draw Michiganders from their winter hibernation and into the fresh air and blooming countryside that our state offers. Whether it’s hiking, mushrooming, or early morning kayaking, the weather has become more and more convincing to get out and enjoy outdoor life. 

One thing that has startled some outdoor enthusiasts is the number of dead fish that they may stumble across on their adventures. With the talk of chemical spills and PHAS contamination spilling into some community's water tables, the sight of large numbers of dead fish, along the shoreline, tends to startle onlookers. 

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The Michigan Department of Natural Resources says that there is no need to be alarmed. It’s just the cycle of life that usually happens each spring thaw. It’s called “winterkill” and the effects are seen following ice and snow cover melts on Michigan lakes. 

So, Just What Is Winterkill? 

The MDNR says shallow lakes with excess aquatic vegetation and soft bottoms are more prone to this problem. It’s especially apparent when a harsh winter causes a deep snowpack that reduces sunlight for the plants. When sunlight is reduced, aquatic plants stop producing oxygen. 

Gary Whelan, DNR Fisheries Division research manager, says, 

Winterkill begins with distressed fish gasping for air at holes in the ice and often ends with large numbers of dead fish that bloat as the water warms. Dead fish and other aquatic life may appear fuzzy because of secondary infection by fungus, but the fungus was not the cause of death. The fish actually suffocated from a lack of dissolved oxygen from decaying plants and other dead aquatic animals under the ice. 

Is Winterkill Restricted to Lakes?
Another area that is susceptible to winterkill is the system of canals in urban areas. Large amounts of nutrient runoff, pollution from roads, lawns and septic systems all add to the problem as they drain from large storm events. 

The victims of winterkill are fish, turtles, frogs, toads, and crayfish. The aquatic life usually dies in late winter and begins to surface a month after the ice leaves the lakes. Fish may also die from rapid changes in water temperature if an unseasonably warm heatwave hits the area. 

If you are out and about on an outdoor adventure and happen to stumble across a fish kill, the MDNR welcomes your report on the issue, just in case it may be something that isn’t related to winterkill. In fact, you can report mammals, diseased wildlife, birds, plants, and more. Just fill out a form at Eyes in the Field, and conservation officers will investigate your concern. 

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