The Minnesota Department of Natural Resources encourages Minnesotans to contact the state duty officer if they see evidence of a fish die-off in a lake or stream. Fish die-offs can result from a variety of natural and human causes.

“People can help by reporting fish die-offs right away,” DNR Limnology Consultant Tom Burri said. “These reports alert state agencies to the situation and help us determine appropriate next steps.”

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.

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. 

In mid-spring and summer, fish die-offs are often the result of warming water and opportunistic infections that spread in fish populations that are already stressed after the spawning season.

When die-offs of wild fish are the result of disease issues, the affected fish tend to be of a single species and size range. By contrast, when die-offs include multiple species and size ranges, human activity is more likely to be the cause.