Minnesota's Lakes Are Cooking Right Now. Here's What That Means for the Fish You Release.

Minnesota's DNR has logged 212 fish mortality reports across 102 waterbodies so far this year, and 65 of those came in a single four-day stretch, July 16 through 20. Surface temperatures on several lakes and on the Mississippi River climbed past 86 degrees. If you've been fishing through this heat wave and wondering whether the fish you're catching and releasing are actually surviving it, the state's own numbers say it's a fair question to ask.

What's Actually Happening Out There

Reports have come in from Lake of the Woods on the state's northern border down to Albert Lea in southern Minnesota, so this isn't a north-woods-only problem. It's showing up statewide. The DNR says northern pike, muskellunge, cisco, and lake sturgeon are among the species turning up in mortality reports, along with larger fish generally across species. DNR Fish Health Supervisor Isaiah Tolo said the state has seen "chronically stressful conditions this summer for fish," with reports of mortality events continuing to come in. The DNR is asking anyone who spots dead or dying fish to report it through their website, which is part of how that 212 number keeps climbing in real time rather than showing up as one big year-end tally.

The Temperature Line Species Care About

Not every fish struggles at the same water temperature, and that's worth knowing before you decide where and when to fish. Cold water species like cisco and other salmonids start showing stress once water passes 75 degrees. Cool water species like northern pike can handle water up to around 84 degrees before it becomes a problem for them. Once a lake or river surface climbs into the mid-to-upper 80s, the way several have this summer, you're well past comfortable for a lot of what swims in it.

The Catch

This is data built from public reports, not a controlled study. The DNR compiles it from what people submit through its website, not from a systematic survey of every lake and river in the state. And 212 is a running count as of late July, a snapshot rather than a final season total.

What This Means Next Time You're Out in the Heat

I already fish this way without ever connecting it to water temperature specifically. Go early, get off the water when it turns brutal, come back out in the evening. That's just how I've always broken up a summer fishing day at the UP cabin, less about the fish and more about not standing in the sun for eight hours straight. Turns out the fish are running their own version of that same math. In the UP, an evening bite after dark has always been just as good for bass as first light, so a hot afternoon doesn't have to mean fewer good hours, just different ones.

If you're catching and releasing fish in this kind of heat, the DNR's actual guidance is worth repeating: be extra careful with thermally sensitive species like pike, muskellunge, and walleye, don't overhandle what you catch, and know that a stressed fish is less likely to survive release than it would be in cooler water, even if it swims off looking fine. My own addition to that, not something the DNR said, is to just get off water that's clearly cooking in the afternoon and come back at dawn or dusk instead. And if you do see fish struggling or dead in the water this summer, reporting it to the DNR isn't just paperwork. It's the same data this whole picture is built from.

Citation

Minnesota Department of Natural Resources. (2026, July 24). Minnesota DNR reports heightened fish mortality during prolonged heat. https://www.dnr.state.mn.us/news/2026/07/24/minnesota-dnr-reports-heightened-fish-mortality-during-prolonged-heat