Each Spring we are asked about Winter Fish Kills and what causes them. But early winter is a better time to be fixing the problem. Instead of waiting and discovering the problem in the spring when it is too late, install an aeration system in the winter.

Frequently, the question comes from people who have just ventured down to inspect their pond after the ice has finally melted off on a beautiful spring day… only to discover heartbreak. They anticipate a beautiful pond, but what they encounter is dead fish.

These are the same fish that they have stocked and fed and enjoyed all last year, now dead, sometimes sunk on the bottom, sometimes floating belly up. This is a frustrating and disappointing moment, but it can be prevented from happening again in the future.

To prevent winter fish kills, the first step is to understand what the real causes are and to dispel a common misconception. The misconception is the idea that the pond “froze to the bottom”, causing the fish to freeze and die. Unless the pond is extremely shallow (less than three feet), this isn’t what happens. Even in extreme Northern Michigan winters, we rarely see ice more than 40 inches thick, usually it is much less than that.

Why does it happen?

So, if the pond didn’t freeze to the bottom, what killed the fish? The primary answer is usually a lack of oxygen. Once a body of water freezes over, it can no longer exchange oxygen and other gases with the atmosphere; the ice essentially seals the top of the pond like a big sheet of plastic wrap. This leaves the pond with only the amount of oxygen that was in the water at freeze to last until the spring thaw. In the meantime, there are lots of biological processes taking place in the pond that use oxygen, such as fish respiration, aerobic bacterial decomposition of weeds, and more. Without oxygen replacement, the pond eventually runs out of available oxygen and fish die.

In addition to the lack of oxygen, other gases can also build up under the ice, again due to various biological processes, and these gases can reach toxic levels. Usually, winter fish kill is caused by a combination of lack of oxygen and the build-up of harmful gases in the water.

How can it be prevented?

The key to avoiding winter fish kill is simply to aerate the pond in winter. Using a properly sized diffused aeration system or circulating de-icers will continually introduce oxygen to the pond as well as maintaining some open water. This open water is important to allow the exchange of gases with the atmosphere, allowing oxygen in and preventing the buildup of harmful gas compounds.

Any aeration is better than none, but best results come from aerating the entire water body adequately. This can be accomplished with several different types of equipment including de-icing circulators and diffused (bubbler) aeration systems. Diffused aeration can be AC Electric, DC Solar, or Wind-Powered. There are many options to fit any pond and any situation, whether the pond is on or off the electric grid.

Selecting the right option for aeration may be a little overwhelming, but we are here to help. We will measure your pond, discuss your goals and experiences, and help you select the system that is right for you. We can even install the system for you. And yes, we can install even if the pond is already frozen over. Don’t wait for the heartbreak of a fish kill, call us now!

Aerating your pond can be simple and we can help you through the entire process from system selection to installation of the equipment. Give us a call or email, or set up a consultation online. We are happy to help!