Minnesota DNR Reports Spike in Fish Deaths Amid Prolonged Heat

The Minnesota Department of Natural Resources (DNR) has recorded a sharp rise in fish mortality across the state as summer temperatures remain unusually high. Surface water temperatures have reached 86 °F (30 °C) or higher in numerous lakes and sections of the Mississippi River, triggering stress in cold‑water species such as lake cisco and salmonids, which become vulnerable above 75 °F. From July 16‑20 alone, the DNR logged 65 reports from 29 water bodies, bringing the season total to 212 incidents across 102 lakes and streams, from Lake of the Woods in the north to Albert Lea in the south.

Officials attribute the deaths to a combination of prolonged heat, accelerated algae growth, low dissolved‑oxygen levels, and nutrient‑rich runoff from urban and agricultural areas. Species most affected include northern pike, muskellunge, walleye, and cisco, which have limited gill surface area relative to body size. The DNR urges residents to report sightings, add shade‑producing vegetation along shorelines, restore aquatic plants, and avoid handling heat‑sensitive fish.

This second “pulse” of mortality follows an earlier wave in June that followed a rapid warm‑up after a harsh winter, underscoring ongoing climate‑related stress on Minnesota’s fisheries.