February 19, 2014 at 8:52 pm

Michigan officials warn of fish 'winterkills' after heavy snow, ice melts

An ice jam on Lake Huron near Lakeside Park in Port Huron. (Todd McInturf / The Detroit News)

This year’s severe winter has been tough on those living in Michigan, but it will most likely be even tougher on fish and wildlife.

The Department of Natural Resources is reminding everyone that after the heavy ice and snow melts on Michigan lakes this winter, it may be common to discover groups of dead fish and other aquatic creatures.

DNR officials call it “winterkill.”

“Winterkill is the most common type of fish kill,” said Gary Whelan, DNR fish production manager. “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.”

Winterkill occurs during long, harsh winters, particularly in shallow lakes with mucky bottoms and excess aquatic vegetation.

Fish and other aquatic life typically die in late winter, but may not be noticed until weeks after the ice leaves the lake because the cold preserves the dead fish, turtles and frogs.

“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 explained. “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.”

According to the DNR, there are various stages connected to the winterkill phenomena.

Dissolved oxygen is required by fish and all other forms of aquatic life. Once the daylight is greatly reduced by thick ice and deep snow cover, aquatic plants stop producing oxygen and many die.

The bacteria that decompose organic materials on the bottom of the lake use the remaining oxygen in the water.

Once the oxygen is reduced and other aquatic animals die and start decomposing, the rate that oxygen is used for decomposition is additionally increased and dissolved oxygen levels in the water decrease even more, leading to increasing winterkill.

For more information on fish kills in Michigan, visit www.michigan.gov/fishing.

If you suspect a fish kill is caused by non-natural causes, please call your nearest DNR office or Michigan’s Pollution Emergency Alert System at (800) 292-4706.

tgreenwood@detroitnews.com
(313) 222-2345