DNR reports more fish kills amid high temps, little rain

Minnesota’s lakes have been less refreshing this summer amid rising water temperatures.

But for fish, a heat wave can be deadly.

The Minnesota Department of Natural Resources has seen a rise in water temperatures and reports of dead fish.

“People should be aware that they might see dead fish," said DNR Fish Health Supervisor Isaiah Tolo in a news release. "We also want them to know what to do to report these events and what actions they can take to protect our fisheries.”

Over 200 fish mortality reports have been submitted so far this year, including several events involving hundreds of dead northern pike.

Certain species, and larger fish in general, are at higher risk when water temperatures rise due to their anatomy.

Nearly a third of the fish mortality events took place over four especially warm days in July.

Cold-water fish such as lake cisco become stressed at 75 degrees. In some places, surface water temperatures have soared to 86 degrees or more.

Consistently high temperatures and little precipitation are affecting a wide distribution of lakes across the state, with varying levels of water quality. Fish are even more susceptible to mortality in lakes with lower water quality.

Water temperatures during Minnesota summers are increasing, and this summer is no exception.

According to climatology data, lakes are about 3 to 4 degrees warmer and have lost an average of almost two weeks of ice cover in the last 50 years.

"Research also indicates that summer fish kills are likely to increase with climate forecasts," the release said.

The DNR encourages anglers to fish with caution, noting that fish are less likely to survive after being caught and released during a heatwave. More information about fish mortality events in general, as well as links to other resources and agencies involved in responding to these events, is on the DNR website.

Homeowners with waterfront property can help fish by providing tree cover at shorelines and growing aquatic plants. Information on natural shorelines and restoration is available on the DNR website.

You can report fish mortality events on the Minnesota DNR website.

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