Expect more fish kills after this winter


Is this year’s winter weather setting ponds up for massive fish kills? The answer is probably yes.

Most ponds could be subject to possible fish kills later this year, attributed to prime conditions brought about by this winter’s extreme weather. The disaster recipe for a fish kill in a pond starts with sustained periods of freezing temperatures, and ice forming over several inches thick, and then a sustained snow pack covering the pond with no sunlight penetrating into open waters below.

This condition for several months will slow production of dissolved oxygen by plants, thus causing the death of algae, further depleting the oxygen fish need as the algae decays in the cold dark condition.

With little or no available oxygen in the remaining open water, fish are subject to a fish kill. They may be dead before you ever see then floating about after a thawing period.

The disaster recipe for a fish kill in a pond starts with sustained periods of freezing temperatures.

Cleanup strategy

What do you do if you have a large fish kill ? According to Phil Hillman, fish management supervisor, District 3, Division of Wildlife, ODNR, winter fish kills should be more likely this year with our longer, colder season. This winter should be more severe than 2010, the last winter with long sustained winter conditions.

Clean up strategies for many dead fish is to actually leave them to further decay and rot away unless you have neighbors real close and odors become a problem. Another strategy is to collect them and bury them. This idea is time consuming and is more appropriate in the summer than winter with better conditions to do the collecting and burial with less resulting odors.

Preventing fish kills

Most ponds should have 25 percent depth of at least 8 feet to provide safe, open water for frozen ponds, but this is no guarantee of stopping a fish kill. It is a least a good place to start.

Shoveling off the snow, if you are that ambitious, will allow some sunlight to get through the ice.

Aerators offer some protections from fish kills if operated through the winter during frozen conditions, although this winter has challenged even aerators to perform successfully.

If you do encounter a fish kill, most Soil and Water Conservation Districts provide fish fingerlings for sale at least once or twice a year. They would be a good source to talk with about your fish and other pond management issues.


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Jeff is the District Manager for the Medina SWCD since 2006. Before that he was an area representative with the ODNR Division of Soil and Water Conservation through out Northeast Ohio for most of his career. He worked closely with District Boards of Supervisors and staffs on programs and capacity building.


  1. I have had this weird bright green color in the pond but it doesn’t seem to be algae. The little feeder fish started dying first and then my beloved and nearly 10 yr old koi. It is a small pond. I want to know how to clean it out.. Empty it all or not? Treat it? So I can restock and try again.
    Thank you!


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