Brutal Winter Turns Up More Dead Fish Than Usual in Suburban Lakes

As lakes slowly begin to thaw, local experts say more dead fish than usual are turning up at suburban lakes. 

DuPage County Forest Preserve District fisheries ecologist Dan Grigas told the Chicago Tribune fishery workers cleaned up 150 grass carp Wednesday at local lakes that weighed about 10 pounds each, which is "about 1,500 pounds of biomass."

Waters at the Herrick Lake Forest Preserve in Wheaton, Cricket Creek in Addison and East Branch in Glendale Heights were among the hardest hit this past winter, according to a Forest Preserve District of DuPage County press release. 

Meanwhile, thousands of dead blue gill, common carp, grass carp, and largemouth bass appeared last week in one of two fishing lakes at Sag Quarries near Lemont, according to the Chicago Tribune. 

But DuPage County rangers and ecologists say the localized incident are no cause for alarm.

“Localized die-offs like these can occur naturally any winter, particularly in smaller and shallower lakes and ponds, and are not a sign that aquatic habitats are in danger,” said Dan Grigas, the District’s fisheries ecologist. “They’re usually a result of seasonally low levels of dissolved oxygen, which start to return to normal as the ice starts to melt.”

Even in winter, submerged aquatic plants use sunlight to produce oxygen through photosynthesis, but when ice and snow prevent light from reaching the plants, the process temporarily stops. This can be detrimental to fish, which need dissolved oxygen to survive.

“Our record-breaking winter certainly created some challenging environmental conditions but nothing unprecedented,” says Grigas. “Still, we’ll continue to monitor all of the Forest Preserve District’s lakes this spring to see if we need to adjust any stocking plans later in the year.”

Anglers can learn more about the District’s 30 fishing lakes on the fishing page.