The Ohio Department of Natural Resources (ODNR) is reminding Ohioans that small numbers of dead fish may be common in ponds and small lakes this spring. Winter die-offs of fish after long periods of heavy ice and snow cover on small waters are known as “winterkills.” Winterkills may occur in some Ohio waters this year as ice and snow of the past few months gives way to spring.
According to the ODNR Division of Wildlife fisheries biologists, minor fish kills do not significantly impact fish populations or sport fishing opportunities in lakes and reservoirs. Fish kills are fairly common in Ohio, particularly right after ice-out, from late April through mid-June, and during prolonged periods of hot summer weather.
Winterkills are caused when persistent ice forms a surface barrier between water and air that prevents circulation of oxygen and blocks sunlight. If these conditions continue long enough, the oxygen fish need to survive may be depleted and result in some or all of them suffocating. Lacking sunlight, plants stop making oxygen and eventually start to use oxygen as they die back and decompose.
Winterkill is most common in shallow ponds and will become obvious if dead fish are seen along the shore. Ohio’s northern counties are most susceptible to winterkill because of colder temperatures and more frequent snowfall. However, winterkill is possible in any part of the state during winters of persistent cold weather and snow cover.
Fish die-offs are possible in Ohio’s larger lakes as well, but for different reasons. Fish which are less tolerant of long, cold winters, such as gizzard shad, are commonly seen along the shorelines of reservoirs and even Lake Erie during moderate winters. However, in larger waters, the species that commonly die off following winter are resilient and return in great numbers following a single spawning season.
Concerned citizens should not attempt to rescue stressed or dead fish. Handling stressed fish significantly reduces their chance of survival, and attempts to capture these fish may present a safety hazard to people attempting to help the fish. Go to wildohio.gov to find more information about fish and preventing winterkills. Large numbers of dead fish should be reported by calling 800-WILDLIFE (945-3543).