Winter Fish Kill and Measures to Take

hole in the ice with diffuser at 3 feetWinter is still holding on, although the snow has gone the ice still stands.

As we do every year we keep a diffuser running near the dock and pier to protect them from heaving in the ice and more important with the open water area we allow toxic gasses that build up under the ice to escape to the atmosphere.

The gasses come from the decaying debris on the bottom of the pond, stuff like fish waste, leaves, plants and weeds that died over winter are all now decomposing building up these gasses and taking up oxygen. This is the worst time of year when fish kills happen and with the extra tough winter we may see plenty of ponds with a fish kill.

It seems I talk about fish kills a lot during winter, spring and sometimes summer, these are the best chances of this occurring but mostly when the ice comes off the pond and the pond flips. Now a little more about fish kills and what does that term really mean? When I started this endeavor of building the ponds and learning various ways of managing the ponds years ago I’ve heard of the pond flipping spring and fall and that those are the times that fish kills could happen.

We stocked the pond in the spring giving the small fish all summer to put some weight on, get acclimated to the pond and have a good chance of survival over their first winter. Once spring arrived we did have around 5-6 fish die the first year. The majority was blue gill and one hybrid striped bass out of the 30 plus fish we put in. If we had an actual fish kill there would have been closer to the entire 30 fish that would have perished.

In the event of a fish kill the big guys would most likely perish first since they need the most amount of oxygen to survive followed by the smaller fish. The actual time of a fish kill is sort of a guess but most of them can occur in the early morning hours when the pond has the least amount of oxygen.

With our small number of fish that died only meant that these poor souls may have had some health issues, they simply didn’t survive the winter months. It also was a sign to get the proper aeration in before we did have an actual fish kill.

What can we do to help prevent a fish kill? There are a couple ways to add quick aeration to the pond but with the ponds being froze over for so long this year we may already be experiencing a fish kill and don’t even know it yet.

A quick couple ways of getting oxygen in the pond is by parking a boat with the motor, actually propeller just under the surface and fire it up to create water movement and let the prop chop or cut the water to create air bubbles and water movement. Fountains are a great source of quick surface aeration, that is if you can get it in as soon as the ice comes off. The whole goal here is to get the water moving and break it up to absorb oxygen. This is a temporary fix to hopefully save some fish.

Even subsurface aeration can work as long as the diffuser is in shallow water. If the pond is 10’ only put the diffuser in a 3’ of depth. If we had the subsurface system up and running all summer long we would have the entire water column full of oxygen. Then once the water cool to 55 degrees we move one diffuser to the shallow area to keep a hole in the ice to allow toxic gasses to escape that is building under the ice. DO NOT drop a diffuser to the bottom of the pond, there are start up procedures when starting a new system at the bottom of the pond and cold weather through the ice can be very dangerous for the fish.

For a long term solution to low oxygen and fish kill prevention use the contact button on top of the site and let us know about your pond so we can help.

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Additional articles,
Summer Fish Kill
Winter Fish Kill
Deicing the Pond
Do Your Fish need More breathing room

About the Author: Darrell Rhoades is the founder of A one man business, works full time in tool & die. It all started when he built his own pond for the family. Ran into pond issues and started the research with pond suppliers and conferences for pond management. He writes about pond building and pond management and sells pond management supplies, aeration & fountains and Practical hands on experiences at . No physical store, but has items in stock.