Pond fish in winter can either come inside with you or, if you have an ecosystem pond, stay in the pond. Pond fish like koi and goldfish are hardy and can survive winters as cold as 32 degrees Fahrenheit. For them to stay outside, the pond needs to be at least 2 feet deep in some areas, have an aerator, and keep a hole open in the ice with a floating de-icer. You can shut off the pumps and remove the filters as long as the de-icer and aerator are running. Stop feeding once the water drops below 50 degrees Fahrenheit, and the fish will rest near the bottom until spring.
Here is how to prepare your pond fish for winter, how to care for them once the ice comes, and when fish should come inside instead.
What a pond needs for fish to survive winter
- At least 2 feet of depth in some areas. That is how deep a pond needs to be for fish to survive the winter. Even in an Iowa winter, water that deep does not freeze solid. Fish rest near the bottom.
- Aeration. An aerator keeps oxygen in the water. Set it higher in the pond, not on the bottom, so it does not stir cold water down to where the fish are resting.
- A hole in the ice. Gas from fish waste and rotting leaves needs a way out, and oxygen needs a way in. A floating de-icer keeps a hole open. It is basically a floating heater for the top of your pond that keeps a hole in the ice for air exchange.
Fish do not need much room in winter. Their bodies slow way down, a lot like a bear hibernating.
How to prepare your pond fish for winter
Winterizing ponds starts in the fall.
Clean out the pond. Leaves and muck on the bottom use up oxygen as they break down under the ice. A fall cleaning removes them. See our fall pond maintenance process.
Adjust feeding as the water cools. Between 60 and 50 degrees Fahrenheit, switch to a cold water food. It is easier for fish to digest. Below 50 degrees, stop feeding. Their digestion slows so much that food can sit in their gut and make them sick.
Watch for predators. Herons and raccoons are hungry in the fall, and fish are easier to catch in clear, cool water. Fall netting keeps leaves out and also helps keep predators away. See our guide to pond netting.
Do an early winter cleanup if you skipped the net. The less there is on the pond bottom, the better your fish do over winter and the easier the spring cleanout will be.
Check the fish. Fall is a good time to look for fish that seem sluggish, have spots or sores, or hang near the surface. A fish that goes into winter sick has a hard time.
Caring for pond fish in winter
- Do not feed them. Below 50 degrees, fish live off their reserves until spring.
- Do not break the ice. Hitting the ice sends a shock wave through the water that can hurt or kill fish. If the de-icer stops working, pour a pan of hot water on the ice to melt a hole.
- Keep the de-icer and aerator running. Check them every week or two.
- Leave the fish alone. Resting fish do best when they are not disturbed.
When fish should come inside
Bring fish in if your pond is shallower than 2 feet, if you cannot run a de-icer and aerator, or if the fish are sick. Fill a large tub with water from the pond. The fish already live in that water, so the move is easier on them. If you use new water, dechlorinate it and introduce the fish slowly so they do not go into shock.
When feeding starts again in spring
Wait until the water is back above 50 degrees Fahrenheit. Start with small amounts of cold water food, then switch to regular food once the water stays above 60 degrees.
Help with winter pond care
Our maintenance plans include fall service and winter shutdown, so your pond and fish are set up correctly before the freeze. For a full winterizing checklist, see how to winterize a pond in Central Iowa. Have questions about your fish? Our fish questions and answers page covers the common ones.
Pond fish in winter questions
Can goldfish and koi survive an Iowa winter outside? Yes, if the pond is at least 2 feet deep in some areas, has an aerator and has a hole in the ice from a de-icer.
How cold can goldfish and koi survive? Koi and goldfish are hardy and can survive winters as cold as 32 degrees Fahrenheit, as long as the pond is deep enough that it does not freeze solid and a hole stays open in the ice.
How deep does a pond need to be for fish to survive the winter? At least 2 feet deep in some areas. Water that deep does not freeze all the way, even in Iowa.
When should I stop feeding pond fish? Switch to cold water food between 60 and 50 degrees Fahrenheit. Stop feeding below 50 degrees.
Is it OK to break a hole in the ice? No. The shock wave can hurt or kill fish. Use a de-icer or melt a hole with a pan of hot water.
Do I need to heat my pond? Most ponds do not need a heater. A floating de-icer that keeps a small hole open is enough for most Central Iowa ponds.
