Dead fish, turtles, frogs, toads and crayfish may be found after ice and snow melt, according to the Michigan Department of Natural Resources. Thick ice and heavy snow have created conditions that threaten fish.
Winterkill occurs during especially long, harsh winters, as experienced this year in Michigan. Shallow lakes with excess aquatic vegetation and mucky bottoms are particularly prone to deaths of fish and other aquatic creatures.
"Winterkill is the most common type of fish kill," Gary Whelan, DNR fish production manager, said in a statement. "Given the harsh conditions this winter with thick ice and deep snow cover, it will be particularly common in shallow lakes and streams and ponds. These kills are localized and typically do not affect the overall health of the fish populations or fishing quality."
Fish and other aquatic life typically die in late winter, but may not be noticed until a month after the ice melts because they're temporarily preserved by the cold water. The fish often suffocate, the DNR said, because of a lack of dissolved oxygen under the ice.
Once daylight is greatly reduced by thick ice and deep snow cover, the DNR said aquatic plants stop producing oxygen and many die. The bacteria that decompose organic materials on the bottom of the lake use the remaining oxygen.
"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 in early spring," Whelan said. "Dead fish and other aquatic life may appear fuzzy because of secondary infection by fungus, but the fungus was not the cause of death."