Minnesota Department of Natural Resources Seeks Help Tracking Fish Kills During Hot Weather

(KNSI) — Hot summer weather is creating stressful conditions for fish in lakes, rivers and streams across Minnesota, and the Department of Natural Resources is asking the public to help report and prevent fish mortality events.

The DNR says it has logged 212 fish mortality reports spanning 102 waterbodies statewide so far in 2026, stretching from Lake of the Woods on the northern border to Albert Lea in the south.

Closer to Central Minnesota, dead and dying cisco have been reported on Lake Koronis in Stearns County.

“We have been seeing chronically stressful conditions this summer for fish and are receiving continued reports of fish mortality events,” says DNR Fish Health Supervisor Isaiah Tolo. “People should be aware that they might see dead fish. We also want them to know what to do to report these events and what actions they can take to protect our fisheries.”

Surface water temperatures have reached 86 degrees Fahrenheit and higher in several Minnesota lakes and in the Mississippi River. Cold water fish like lake cisco and other salmonids become stressed when temperatures climb above 75 degrees, while cool water species such as northern pike can handle water up to 84 degrees.

The Fish Health Laboratory received 65 reports covering 29 waterbodies in a four-day stretch from July 16th through the 20th. The DNR says fish are especially vulnerable in lakes carrying excess nutrients from urban and agricultural runoff, where decomposition and algae growth speed up and dissolved oxygen drops.

This is the second “pulse” of elevated fish deaths this summer. The first came in June, following a rapid rise in temperatures after a cold winter, and mostly affected lakes in the Twin Cities metro. The current pulse, driven by steady heat and little rain, is hitting a wider range of lakes across the state.

Species sensitive to high temperatures are among the hardest hit, including northern pike, muskellunge and cisco, along with larger fish of all kinds, which have less gill surface relative to their body mass. Some events have reported hundreds of dead northern pike with few other species affected. Large lake sturgeon have been washing ashore on Otter Tail Lake in Otter Tail County.

Anyone can report a fish mortality event by clicking here.

https://survey123.arcgis.com/share/c891b8ed820649cf85a236c38890aeba?portalUrl=https://mndnr.maps.arcgis.com

“Reports from members of the public are an important way we receive information about fish mortality,” says Tolo. “Those reports reach an interagency team of fish and water quality professionals.”

Waterfront property owners can help by protecting and restoring natural shorelines, encouraging tree cover and aquatic plants that create cooler thermal refuges for fish. Riparian and non-riparian landowners alike can reduce nutrient runoff into lakes and rivers. The Minnesota Pollution Control Agency offers tips on preventing runoff and restoration.

Anglers should also use caution during heat waves. Fish stressed by warm water and low oxygen are less likely to survive after being caught and released, so the DNR advises avoiding overhandling, especially when targeting sensitive species like pike, muskellunge and walleye.

More information is available on the DNR website by clicking here.

https://www.dnr.state.mn.us/fisheries/fishkills.html

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