Fish Kill Reports Expected to Rise as Ice Thaws

Coyote on Ice, Frash Pond in Stratford (CT) on February 24. Photo/Connecticut Fish and Wildlife/Henault Caporaso
Coyote on Ice, Frash Pond in Stratford (CT) on February 24. Photo/Connecticut Fish and Wildlife/Henault Caporaso

The Connecticut Department of Energy and Environmental Protection (DEEP) has issued a notice reminding the public that the long, cold winter, with extended periods of snow and ice cover across the state, has greatly increased the potential for fish kills in shallow ponds and lakes.

Conditions this winter have been similar to those experienced 3 years ago, when DEEP received numerous reports of dead fish in lakes and ponds as ice cover finally receded.

Winterkills occur most frequently in very shallow, nutrient-enriched ponds that are subject to abundant growth of aquatic vegetation,” said Peter Aarrestad, Director of DEEP’s Inland Fisheries Division. “Conditions conducive to winterkill arise when heavy snow cover over ice inhibits sunlight penetration, thereby preventing aquatic plants and algae from producing oxygen via photosynthesis. This process is the sole means of oxygen creation under ice-covered ponds. The fish typically die during the winter and are only observed following ice-out.”

Winter kills that occur in larger lakes are rarely serious in the long run because lakes support thousands of fish per acre. Usually enough fish survive, either in the lake or in connecting waters, to repopulate the lake. More severe winterkills that result in the elimination of all or nearly all of the pond’s fish community are more likely to occur in very small ponds, which are often privately owned. Pond owners who experience winterkill are advised that in the future, shoveling off some of the snow cover to allow light penetration may stave off potential winterkill conditions.

Anyone observing abnormally high fish mortalities during or after the time that ice is melting can notify the DEEP Inland Fisheries Division in Hartford (860-424-3474), the Eastern District Office in Marlborough (860-295-9523), or the Western District office in Harwinton (860-485-0226).

The public is also advised that any fish kills observed in rivers, lakes, ponds, and streams any time of year can be reported to the Inland Fisheries Division at the numbers listed above. While most fish kills are natural occurrences, some have been attributed to accidental or unauthorized human actions such as chemical releases, agricultural runoff, flow modifications or poorly designed or conducted management activities. Anyone reporting fish kills is asked to provide as much detail as possible concerning location, time and date, estimated size, numbers and types of fish involved, and other relevant site-specific information, and if possible, photographs or digital images. A fact sheet with more information on winter fish kills can be found at