Winterizing your pond is one of the primary ways to ensure your fish are happy and healthy throughout the winter. This involves removing waste at the end of fall so there is no excess waste or organic material decomposing in the water during the winter. You'll want to deice or use a heater to prevent ice from fully covering the pond. Toxic gases build up underneath the ice as waste and organisms decay. These gases can be harmful or even deadly to fish and severely lower your water quality. Allowing an open space for them to escape will prevent this from harming your fish.
In nature, fish survive winters by entering a period of dormancy where their metabolism greatly slows and they begin exerting less energy. Fish are alerted to this incoming change as food stores become less common due to the changing of the seasons. You can simulate this in your pond by reducing the frequency of feedings once the water drops below 70 degrees. Once the temperature drops below 50 degrees, you can cease feedings entirely until things warm back up.
