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How Low Oxygen and Toxic Gas Contribute to Winter Fish Kill

Changing seasons always present new challenges to pond owners. Although winter upkeep may seem like a pain, it is extremely important to do a little maintenance to ensure that your fish survive until the next spring. The good news is that a small amount of effort at the beginning of the season can make a drastic difference in the long-term outcome for your pond.

Winter Fish Kill

“Fish Kill” is a term that refers to when a significant portion of the fish population die in response to changes in their ecosystem. This can be caused by a number of issues. These are some of the most common winter issues and their solutions.


When the weather gets cold, fish metabolisms slow down significantly. This means that they need less food and less oxygen than in the warmer months. However, they do still need some to make it through the winter. When a pond freezes over, the exchange of atmospheric oxygen and the natural buildup of gasses in your pond stops (oxygen depletion and toxic gas buildup). Unfortunately, those gasses can be toxic to your fish, and can result in a high mortality rate.


The simplest way to fix this issue is to aerate the pond. Aeration works by churning your water, allowing an exchange of the toxic gasses with atmospheric oxygen, and preventing a portion of the pond from freezing over. There are many aeration options available, including diffusers, windmills and solar aerators. Check out our other posts on each type, or contact us for help deciding what type is right for you!

Another option is to help the ice melt naturally by removing the snow from a portion of the pond on warmer days. This lets the sun penetrate the ice and allows for melting. Normally the snow cover insulates the ice too much for this to happen. Of course, this method is only effective in more moderate climates and at certain points in the winter, so it is best not to rely too heavily on this technique.

For more information, or assistance in creating a pond plan tailored to your unique needs, call us toll free at (877) 389-2514, or email us at!