Prolonged Snow Cover May Lead to Winter Fish Kills

Prolonged periods of snow cover this winter along with thick ice and shallow water may increase the number of dead fish (fish kills) found on Lake County's lakes and ponds. Fish kills should be reported to the Lake County Health Department/Community Health Center.

"The winter fish kill is generally caused by low oxygen stress," said Mike Adam, a senior biologist with the Health Department. "Once snow covers the ice and blocks sunlight, less oxygen is produced in the water. Fish become stressed as the oxygen becomes depleted."

Unfortunately there is not much that can be done about such occurrences. In some cases, removing some of the snow cover from the ice surface may be helpful to allow sunlight to penetrate. If a winter fish kill has occurred, the dead fish may not be seen until after the ice has melted. Dead fish on the shore should be collected and disposed of in the trash.

Winter fish kills affect many sizes and species of fish, and tolerance for a lack of dissolved oxygen varies among species. Trout are the most sensitive; walleye, largemouth bass, and bluegill have intermediate sensitivity; and northern pike, yellow perch, and pumpkinseed are relatively tolerant. Bullheads and certain minnows are very tolerant.

Only in the case of an extreme die-off is restocking a pond or lake necessary. Usually enough fish survive, either in the lake or in connecting waters, to repopulate the lake in a couple of years. A fisheries survey should be conducted to determine the extent of the damage done by the fish kill before any stocking program is initiated. If you have a local lake or pond that experiences a fish kill, report it to the Lake County Health Department's Ecological Services Program, at (847) 377-8030.

For more information on lakes management, visit health.lakecountyil.gov/Population/LMU/Pages/default.aspx.