How to save pond fish

Q. I’ve heard that there can be problems with ponds from winter to spring. How can I be sure my fish don’t die?

George from New Middletown

A. Many people have ponds in Ohio – large ones (lakes) and small ones. No matter the size, there is something that must be addressed in the life cycle of each pond. This is the issue of pond turnover. I have about a quarter of an acre pond and have had winter fish kill twice.

With some planning, you might not have to deal with the same issue that I have.

Water in ponds has many different temperatures – the top is warmest from the sun, the middle range is moderate, and the bottom is the coldest and the most dense. This is called water stratification.

In the winter, when water on top gets cold – approximately 39 degrees is most dense – it sinks, thus forcing the cooler water up, which is less dense.

This creates a mix or “turn over.” The bottom water forced up has less oxygen due to less or no sunlight.

Plant decay, bacteria and fish take up the oxygen, depleting the much needed gas, causing the fish to die. This is winter fish kill.

Other factors are snow on ice on the pond.

Even with ice – water expands at 34 degrees and freezes at 32 degrees – the presence of sunlight can allow photosynthesis to take place in the submerged water plants. This replenishes the oxygen used up.

So, removal of snow from ice on the pond is vital.

You must be careful when doing any activity on ice as it is hazardous work. If you haven’t had an issue yet this year, you are probably in the clear for this season.

To prepare for next winter, make plans to clear snow from the ice.

Many pond owners use aeration devices during in winter to replenish the oxygen and allow fish to survive. They not only replenish oxygen, but they allow for a bit of free water for gas exchange.

We use an aerator. With this device, we have not had winter fish kill, and our pond is flourishing.

To learn more about fish kills and how to prevent them, go to:

Also, join me from 9:30 a.m. to noon Monday at the OSU Mahoning County Extension Office, 490 S. Broad St., Canfield, to learn about garden ponds, caring for them, planting them and much more. Call 330-533-5538 for information. Details also at:

Today’s answer provided by Stephanie Hughes, Ohio Certified Volunteer Naturalist. Regular hours for the clinic resume April 2. Submit questions to the clinic or drop samples off to the extension office in Canfield.

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