The Iowa Department of Natural Resources (DNR) has received numerous reports of dead fish in lakes and ponds across Iowa as the ice cover disappears for another year.
Winter fish kills are common on Iowa shallow lakes during long winters with lots of snow cover. When lakes freeze early and receive a blanket of snow, it effectively shuts off the sunlight from reaching aquatic plants, which stops photosynthesis and the flow of oxygen into the water. The longer the ice and snow cover the lake, the less oxygen is in the water and available to the fish.
Signs of winter kills are visible shortly after ice-out when fish that died during the winter float and are blown to shore. In certain lakes, like Rathbun, Black Hawk, Storm and Coralville, these dead fish are often a source of food for channel catfish that will go on a feeding spree. Many anglers see this as an early season fishing opportunity for trophy-sized channel catfish.
“Winter kills are rarely complete kills. We get a lot of calls from farm pond owners who think they lost all of their fish in their pond to winter kill,” said Joe Larscheid, chief of the fisheries bureau for the Iowa DNR. “Our advice to them is to fish the pond in the spring, note the species, number and size of what you catch and talk to their local fisheries biologist about the health of the pond.”
Natural lakes winterkill from time to time and are part of the natural cycle. Fisheries staff are watching lakes and ponds with low oxygen levels that are at risk of having a winter fish kill. Many Iowa lakes and ponds are still under ice, so additional smaller, shallow ponds and lakes might have winter kills after the ice disappears.
While Mother Nature may be responsible for many fish kills discovered after ice-out, the Iowa DNR would like to make sure some other factor is not to blame.
“If in doubt, give your local fisheries biologist a call so we can discuss your situation,” Larscheid said. Find contact information for your local fisheries biologist on the DNR website at www.iowadnr.gov/About-DNR/DNR-