Overwinter Fish in your Pond
Many pond owners with deeper ponds choose to overwinter their fish outdoors. When overwintering fish in the pond, you'll want to remove nearly all the pond equipment besides an aerator. Once the pond shuts down, there isn't too much to do other than check on your fish and make sure there are no major issues. Learn more about how to overwinter fish in the pond.
Is Your Pond Deep Enough?
The biggest concern with overwintering fish outdoors is whether or not your pond is deep enough. During the coldest parts of winter, your pond must not freeze all the way through. There should be enough unfrozen water at the bottom of the pond for your fish to comfortably live until spring. During the winter, fish are less active because they're cold-blooded and need less room to swim than usual.
As a rule of thumb, ponds must be at least 18 inches deep, ideally 24 inches or more, to overwinter fish. If you have larger fish like koi or live in an area with severe winters, your pond may need to be even deeper (48 to 60 inches) to avoid freezing.
Before the Freeze
Once the pond's surface freezes, your main jobs are to keep an eye on your fish and make sure there's an open hole in the ice for oxygenation. Before the water begins to freeze, getting the pond ready for shutdown is essential. Remove any debris you can so the pond is as clean as possible. The beneficial bacteria aren't active in the winter, so any debris will sink to the bottom of the pond and slowly decay.
Winter Fish Feeding Schedule
Because fish are cold-blooded, they require heat from their environment to digest and metabolize food. As the water gets cooler, you can feed your fish less frequently and add wheat germ to their diet. Once the water in the pond drops below 50°F, they do not need any food. Learn more about feeding your fish as the weather gets cooler.
Remove Pond Equipment
When the pond's water drops to 40°F, the pond pump, fountain, and other equipment and decor should be removed to prevent overcooling and damage. During the winter, the water at the deepest part of the pond is the warmest. The water closest to the surface is the coldest. Overcooling occurs when the colder surface water quickly mixes with the warmer water at the bottom of the pond, causing the warmer water to become cold suddenly. The rapid drop in temperature stresses pond fish.
It's important to keep a section of the surface ice open to allow toxic gases to escape as debris breaks down. Move the aerator to a shallow area of the pond. The aerator will circulate the section of water and keep it from freezing. If the water keeps freezing over, you can use a de-icer to prevent ice from forming. You can also pour warm water on the ice to reopen the section. Avoid using force, as it can cause stress to your fish.
Once the Pond Freezes over
Snow can prevent sunlight from reaching the pond water. Sunlight is essential, as it lets plants and microorganisms in the water photosynthesize. You can use a snow blower, shovel, rake, or broom to remove snow from the pond's surface.
Checking In On Your Fish
During the winter, fish are more vulnerable to sickness and stress as their immune systems are less active. Periodically check to make sure there's a section of the ice open so the water can oxygenate and release harmful gases, and keep an eye out for any sick fish. Once the water starts to warm up, you can begin planning your reopening.
If a pond is large enough during the winter, koi, goldfish, and other hardy fish can congregate or gather at the bottom of the pond. The unfrozen water at the deepest point is the warmest. Fish are cold-blooded, so their metabolisms slow as the water cools, and they will stay at the bottom of the pond, barely swimming and not eating until the spring. Preparing your fish to overwinter outdoors takes care to make the transition smooth. Once the surface freezes, there is little to do but sweep away snow, make sure a section of the ice is kept open, and keep an eye out for any major issues in the pond.