With recent ice-off on area lakes, residents may notice dead fish washing up on shore. This is known as winterkill, or winter fish die-off. Winterkill is a natural process that happens from time to time in most shallow, urban lakes. This year we have received reports of winterkill at a few of our area lakes.
Winterkill can happen when there are low oxygen levels in the water. Low oxygen levels can be caused by:
- Early snow and ice, which reduces sunlight, stopping plants from making oxygen
- Shallow water levels
- Fish using up the available oxygen
Winter fish kills rarely result in the death of all fish in a lake and may even help naturally kill invasive common carp. After a winterkill event, residents can expect dead fish washing up on shore, foul odor due to decomposition, and an increase in scavenging animals eating the dead fish. The Minnesota Department of Natural Resources (DNR) recommends either leaving the fish to decompose naturally or removing and burying them.
In general, winterkills will not have a significant negative impact on water quality and can provide some benefits, like reducing carp populations.
If you find a fish kill of the same fish size and species in the spring, the cause is most likely disease related. As fish spawn and compete for food in shallow spring waters, their bodies get more stressed, making them more susceptible to disease and infection.
The Minnesota DNR tracks fish kills; to report a fish kill, call the DNR at 651-649-5451. More information can be found on the DNR website: https://www.dnr.state.mn.us/fisheries/fishkills.html