Monday, February 22, 2021

Winter kill: Coming to a pond near you


The winter of 2010-2011 was not kind to local landowners who have bass ponds on their property. Most ponds in the area froze over on Thanksgiving and didn’t thaw until Easter. We weren’t blessed with the periodic thaws and rains that keep smaller local waters ice-free or a little open on occasion in the winter months.

That ice cap resulted in significant winterkill and many disappointed anglers that spring as carcasses of fish, large and small, washed up on shore. The ponds on our farm were hard hit – our walleye population was completely decimated and trophy-sized bass in excess of 5 pounds littered the shoreline.

It was really heartbreaking. You do everything you can to manage a decent recreational fishery for your family and then Mother Nature has her own plans.

In the decade since, ponds faced with that adversity had recovered. It takes a while to grow trophy bass in this area as our “growing seasons” are too short. But, we were finally getting back to the glory days (the only setback being a far less potent winterkill in 2014-2015).

But, as close as landowners were to revitalizing their fisheries, this winter happened.

This hasn’t been a drawn-out freeze (most local ponds didn’t glaze until Christmas), but the severity of the cold, the depth of the ice and the amount of snow cover atop the ice all mean that a winterkill is in the cards, and one that will likely rival 2015’s and maybe put it in the same league as 2011.

How does winterkill happen?


Fish, like all animals, need oxygen. The oxygen they breathe in the water comes from two sources: The byproduct of photosynthesis of algae and weeds growing in that pond and the oxygen that enters the water from the air. Winterkill occurs when ice and snow together cover a pond and prevent both of those from occurring.

Ice cover will, of course, prevent oxygen from entering the water from the air and wind agitation. And, looking at the long term forecast and trends, we’ll have ice on small local ponds non-stop for two-and-a-half to three months.

But that’s not the primary cause of winterkill. If it was, most area ponds would have significant die-offs every year.

It’s the snow that’s the killer. Unlike a normal winter (whatever “normal” may be), we’ve been besieged with a lasting snowpack. Depending on where you are in Western New York, most ponds have been under snow for 4 to 6 weeks now. A good melt – especially in the lake snow belts -- might not happen until March.

That snow prevents sunlight from entering the pond. Sunlight is necessary for photosynthesis which still occurs even in the coldest months. So, when the plants can’t get what they need, they don’t grow (and create oxygen) and then they die. Plant decomposition then consumes the oxygen that was needed by the fish. Smaller, shallower ponds without deep holes or underwater springs and with a high density of plants and bass and panfish will be especially hard-hit.

The fish die a miserably slow death. Basically, they suffocate.


It’s likely that you already have dead fish in your pond. You won’t know it until two or three weeks after ice out. Their corpses are somewhat preserved by the cold water now, but as the water warms and oxygen is introduced to the water, decomposition will speed up, the fish will become buoyant and they will end up on shore. Their bodies will be white, maybe even fuzzy, which is a fungus created by rotting.

Winterkill can be prevented, allegedly, with small commercially-available windmills. But, they don’t work well in frigid winters like this as their wheels freeze over with ease. Some folks also suggest that you periodically run a small outboard motor for a few hours at a time every few days. With the likelihood of freeze over on a daily basis, that’s also an impractical option.

Good long-term pond management can also cut down on winterkill rates by ensuring there is not too much plant life in your pond which consumes a lot of oxygen when it dies. To do that, you would have to use a weed rake in the summer and/or introduce grass carp to the pond. But, you can’t remove all plant life, because you still need those oxygen producers to do their thing in the winter.


Regardless, for most of us, it’s too little, too late to save this winter.

If you are a fisherman it will be yet another depressing event from a winter that’s been made depressing enough by Covid and government’s response to it. This spring and summer, fishing on your pond might not be the cure for cabin fever that you had hoped it would be.


From the 15 February 2021 Greater Niagara Newspapers and Batavia Daily News

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