During the colder parts of winter, your pond should not freeze completely. There should be enough thawed water at the bottom of the pond so that the fish can get out of the winter. As a general rule, ponds should be at least 18 inches deep, ideally 24 inches or more, for fish to winter. There are several issues to consider when caring for pond fish as the days get colder.
First, your fish need a pond depth of at least 18 to 24 inches or more in order to successfully winter. If your pond is shallower, you'll need to find new rooms for them during the winter months. Regardless of the depth of the pond, it is best to take sensitive fish such as exotic goldfish indoors during the winter. Once temperatures drop to 50°F, refrain from feeding fish.
They need to prepare for hibernation and you'll want to avoid any metabolic complications. In warmer climates, where the pond doesn't freeze, 4 feet is sufficient. In temperate climates with mild to cold winters, a depth of 7 to 8 feet is preferable. In locations with extremely cold climates, a depth of 12 to 21 feet is best.
Place a pond aerator or submersible pump on the second shelf of your pond so that it bubbles right on the surface of the water. If you choose to close your waterfalls during the winter, first unplug the waterfall pump, remove it from the pond or skimmer, and then store it in a frost-free location. Keeping your pond running during the freezing winter months will allow you to enjoy the beautiful ice sculptures that form in the stream and waterfall. Any organic waste, such as leaves, fish debris, and dead vegetation, present in the pond will consume dissolved oxygen as it decomposes.
As long as your pond doesn't freeze to the bottom and a vent hole is provided on the pond surface, your fish will survive the winter. Pond Informer is a growing community of pond professionals, environmentalists and science writers %26, passionate about everything related to ponds, wetlands and sustainable conservation. However, many ornamental pond fish species have been marketed around the world and are often unable to fully acclimate where they end up. Other fish can be buried partially or completely in the sediment at the bottom of the pond to keep warm, where they also enter a period of inactivity.
In freshwater systems with sufficient depth, warm water deposits on the bottom (or hypolimnion) of the lake or pond during the winter due to its higher density, while cold water rises in cycles to the epilimnion (surface) and can freeze (this is called winter stratification). If the water cools too quickly, many fish will fall into shock and become ill, which is why some pond owners in very hostile climates report massive fish deaths during sudden cold spells. Both involve passing pond water through fairly effective heating chambers in the devices and then pumping the heated water back into the pond. In general, keeping water below about 85° F (about 29° C) will support healthy dissolved oxygen levels and keeping ponds below this temperature in the warmer months is ideal.
If your pond is at least two feet deep, the proximity of the land to the pond surface will prevent the pond from freezing to a depth greater than eight inches.