Winterkill is a serious threat to your fish population if you live in the north. If large amounts of snow and ice form on your pond or lake, it can block out sunlight from penetrating into the water. Without sunlight, plants will die, thus ceasing to give off oxygen they would produce during photosynthesis. The dead plant material also provides added nourishment for bacteria which also use oxygen. As the winter progresses, the available oxygen in the pond can be used up to a point where fish can suffer.

In the winter, the metabolism of fish will slow down. They move less, eat less, grow less, and use less oxygen. The same goes for bacteria in the pond, the oxygen consumption is lower. However, oxygen levels can drop low enough to cause major problems in a pond if the winter is severe enough. In many cases, the larger fish of a given species will consume more oxygen. Therefore, during low oxygen times, your biggest fish can die.

Luckily, winterkill can be prevented. Cold water has the ability to hold more dissolved oxygen than warm water. In the winter, the water is very cold and has the ability to hold more than enough oxygen to support the fish in your pond; it just needs to be exposed to the air so oxygen from the air can diffuse into the water. This is where Kasco comes in.

Using a Kasco de-icer, water circulator or diffused air system, you can keep the water open so oxygen has a chance to diffuse into it and your fish can survive. A large open water area is not needed to prevent winterkill either. Only about 1-2% of the total surface area of the pond or lake needs to be open to prevent winterkill. In larger ponds or lakes, it is recommended to have several smaller open water areas, rather than one large area. Fish will migrate to the areas of higher oxygen during low level times. Remember to check with local regulatory agencies about requirements of marking off open water areas along public water ways and always be extremely careful around open water in the winter.

Some best practice habits are to keep and maintain your open water area touching shore. This is a safety issue for pets and wildlife. If a dog or a deer falls into the open water area in the middle of the pond or lake, they have no way of getting out. However, if your open water area touches shore, they can safely swim out.

If using a diffused air system in your pond, it is often best to cut back on the air flow during the winter. If you use 3 diffusers to aerate in the summer, you may only need 1 to run during the winter for de-icing. The danger is moving too much water and “super-cooling” it to levels that could be dangerous to fish and/or make your ice thicker, eventually closing off the open water. Pulling a diffuser head to shallower water near shore is another option that also solves the animal safety issue above.

By maintaining open water, you are ensuring your fish are thriving, even during the cold weather. They will have more oxygen which will lead to less stress and the ability to fight disease better. They will also be more active and able to feed more and hit the ground running when the warmer spring water arrives.