The first snowfall of the winter is exciting as we hideaway in our homes with a cup of hot chocolate watching the beautiful white snow blanket our yards. We notice how pretty our water garden looks glittering with white but then panic sets in when we realize it has frozen! No need to panic. We have you covered with what to do if you pond freezes over.
Assuming your pond has entered the frigid cold in a healthy state, without a lot of decaying leaves and debris on the bottom, and not overstocked with fish, everything should be okay. One preventative measure is to check that any submersed pumps are kept deeper than possible ice levels.
When a pond freezes over it forms what would best be defined as an ice cap. This ice cap will generally cover the surface of the pond, but it is not airtight and can still allow airflow. Ponds freeze from the top down and very rarely freeze solid all the way through. When you see a frozen pond it is only ice capped which will slow down the oxygen intake and ammonia release of the pond, but it does not stop it.
Cold water usually has a good amount of oxygen dissolved in it, and any fish and wildlife, lethargic in the cold, will be using up less oxygen. If this is the case, aquatic life should be able to cope with the surface being ice capped for a few days without being in any serious danger. However, if the surface stays completely sealed for more than a few days, problems might arise for the pond inhabitants. The oxygen levels may start to fall, and dissolved waste gases, like ammonia, may start to build up in the water. This is especially a problem where the pond is heavily stocked with fish; has a lot of debris on the base; or has snow lying on the ice, stopping light from reaching underwater plants. If there is snow lying on top of the ice try to use a long handled broom to clear the snow, as noisy shoveling can be abrasive to dormant fish. This will also allow light to be shed into the pond for our aquatic plants to do their jobs, creating oxygen.
To allow for gas exchange, keeping a hole open in the ice is a good idea. Breaking a hole in the ice can stress fish, so try quietly melting a hole in the ice if you need to by pouring boiling water from a kettle at least twice a day. You can also use a small floating pond-heating unit or a deicer. An aerator can also be used during the winter to keep an open area in the ice but even if it gets frozen over aerators are still degassing the pond and moving that pocket of air in between the pond water and the ice cap.
If the forecast predicts icy weather, it is advised to turn off fountains and pumped ornaments. During short spells of freezing temperatures, leave pumps or filters running. The movement of water will help to keep an area of the surface free of ice, will maintain beneficial bacteria in the biological filters, and will circulate the water helping to produce oxygen. However, in situations where prolonged freezing ices up water features like waterfalls, causing water loss, you may be forced to turn pumps off. Be sure to drain all the water out of filters and pumps to prevent water freezing and splitting the casing. Once the ice has melted, if the pond smells stale execute a partial water change and use chlorine remover if necessary.
Follow these preventative guidelines to avoid an ice cap but if you are in an emergency these tips will help to keep your pond from distress.