The Iowa Department of Natural Resources has received numerous reports of dead fish in lakes and ponds across Iowa as the ice cover disappears for another year.
These winter fish kills have been reported at Swan Lake (Carroll), Badger Creek Lake (Madison), Clark Lake (Cerro Gordo), Kuhn Wildlife Pond (Cerro Gordo), Pilot Knob Pond (Winnebago), Alice Wyth Lake (Black Hawk), Middle Sabula and Green Island lakes (Jackson), Credit Island Lagoon (Scott), and a storm water retention pond in Guttenberg.
Fisheries staff are also watching lakes and ponds with low oxygen levels that are at risk of having a winter fish kill. Many north Iowa lakes and ponds are still under ice, so additional winter kills are likely.
Winter kills happen when a combination of ice and snow blocks sunlight from reaching aquatic plants, which in turn, stop producing oxygen. The longer the snow and ice cover lasts, the less oxygen is in the water.
"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. 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," said Joe Larscheid, chief of the fisheries bureau for the Iowa Department of Natural Resources.
"What is important to understand it that this is a natural phenomenon and has been occurring in lakes, ponds and river backwaters throughout our history," Larscheid said. "On the positive side, winter kills create a surplus of food that allows the remaining fish to experience rapid growth over the following year or two."
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.
"Channel catfish are attracted to food that gives off a strong odor and these dead fish put off an odor that will bring in catfish from across the lake. We tell anglers to fish on the windblown shore this time of year because the dead fish will be there, followed closely by the catfish. This can be some of the best fishing of the year," Larscheid said.
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.