In early spring, the retreat of lake and stream ice can sometimes leave behind fish that died during ice cover, commonly referred to as winterkill. When snow and ice cover a lake, sunlight reaching aquatic plants is limited. The plants, in turn, reduce the amount of oxygen they produce. If vegetation dies from lack of sunlight or other cause, the plants start to decompose, which uses oxygen dissolved in the water. If oxygen depletion becomes severe enough, fish die.

The Minnesota Department of Natural Resources encourages Minnesotans contact the state if they see evidence of a fish die-off in a lake or stream. These fish die-offs happen occasionally and can result from a variety of causes.

“People can help by reporting fish die-offs right away,” DNR limnology consultant Tom Burri said. “These reports help us determine whether an investigation is needed.”

To report fish die-offs, people should call the Minnesota Duty Officer at 651‐649‐5451 or 800‐422‐0798 (the officer line is available 24 hours per day, seven days a week). An early report allows timely water and fish sampling or other response actions, if needed. It’s especially helpful to know what sizes and types of fish people see in a fish die-off.

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