Should You Turn Off Pond Pumps in Winter? (The Facts)

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Koi pond in winter
In most cases, it’s prudent to keep your pond pump running through the winter, especially if you have aquatic life in your pond. Scottb211 / CC BY 2.0

Now that temperatures have significantly dropped and prolonged freezes are more likely to occur, you may find yourself wondering whether your pond and its inhabitants can fare well through several more weeks of winter. In zones with mild climates, it is far more straightforward to ensure that pond equipment can last through the season. In harsher temperate regions, however, some extra care may be necessary to prolong the life of pump and filter machinery.

In winter, one of the most important parameters for fish survival is dissolved oxygen. When the water’s surface freezes up, preventing the exchange of gases between your pond and the atmosphere, fish kills may eventually occur. This is due to the buildup of potentially dangerous gases in the pond itself and the loss of oxygen in the water. While pond plants may, to some extent, aid in providing supplementary oxygen, they are rarely productive enough to support the survival of a community of ornamental fish in winter.

Pond pumps are particularly crucial in the winter. Your decision to leave one switched off through the season would depend on several factors, but, in most cases, it would be prudent to leave it running. The understandable impulse to switch a pump off may spring from fears that its tubing or internal components might freeze and break, but keep in mind that the running water should help prevent breakage.

Factors to Consider When Running a Pump Through Winter

Although some pump manufacturers may recommend switching off a pond pump, especially in outdoor water systems that do not contain heaters, a seasoned pond expert will often advise you to keep it switched on. On its own, a pump runs as a filtration/circulation system that should not be in danger of freezing if water continues to run through it and it is located in the right area of your pond. In ornamental fish ponds, the pond pump should essentially be running day and night all through the year.

1) Location of the pump

Submerged pond pump
Leaving fully-submerged pumps that are designed to be operated at low temperatures turned on throughout the winter should be safe. / CC BY 2.0

If your pond pump is fully submerged and has been designed to operate at low temperatures, it should be safe to leave on throughout winter. Ideally, the pond pump should be situated at least one foot above the pond bottom, where the water density and temperature are higher than that of the pond’s surface. Moving the pump to a shallow area or situating it further away from the bottom of the pond should help prevent the colder surface water from mixing with the warmer bottom layer.

If your pond pump pushes water through an exposed filter, perhaps placed along the unprotected side of a pond, some components of your machinery may become damaged during a deep freeze. Insulating exposed equipment should help prevent them from freezing and cracking during prolonged cold spells. Unless they are exposed to extreme temperatures, pipes that are continuously innervated with running water should not freeze.

2) Water depth

Koi pond
Ornamental fish require a pond depth of at least 3 – 4 feet to remain comfortable under ice; they are unlikely to survive in frozen shallow ponds. Alkan de Beaumont Chaglar / CC BY-SA 2.0

Your ornamental pond should be deep enough to have a bottom layer of warmer water through the coolest weeks of winter. If it is too shallow and is likely to freeze over almost completely, it would not be ideal to keep pond machinery running. Don’t forget that ornamental fish are also unlikely to survive in shallow ponds that freeze over. They require a depth of at least 3 – 4 feet or more to remain comfortable under a layer of ice. If you’re determined to keep a shallow pond functional and occupied with fish through winter, a heater or pond de-icer may be necessary.

3) Aquatic life in your pond

Outdoor koi pond
Although ornamental fish may move and eat less during the winter, they still require oxygen to breathe. Tim Pierce / CC BY 2.0

Though ornamental fish may enter a stage called “torpor”, during which they will eat and move less, they will continue to require oxygen to breathe. Oxygen is also necessary for the continuous breakdown of fish waste. Ponds with koi, goldfish, and other long-lived organisms should definitely be supported by circulating water, via a pump. The water should not be allowed to grow stagnant. Ponds that are devoid of high-value plants and animals may not require a functioning pump through winter.

4) Pumps for a waterfall or fountain

Pond waterfall in winter
If you have a separate pump for water circulation, it should be okay to switch off the pumps for your water features through winter. liz west / CC BY 2.0

Water features that are used to help oxygenate a pond or add to its visual appeal are usually switched off during winter. Their exposed design can cause their surfaces’ temperatures to drop considerably, causing any water that flows on or through them to freeze due to direct exposure to the cool air. In the case of waterfalls, continuous use through cold spells can create miniature dams that divert the water to an area outside the pond.

As long as a separate pump is used for water circulation, the pumps that are used for these specific features may be switched off. Ideally, your pond design should allow for switching any water features off without affecting your main recirculation system.

A Running Pump Supports Beneficial Bacteria

Ornamental fish pond
As it can take a long time to establish thriving populations of beneficial bacteria in ornamental ponds, switching off your pump during winter may undo months of hard work. Tim Schofield / CC BY 2.0

It may take weeks, months, or even years for an ornamental pond to successfully mature and have thriving, self-sustaining populations of beneficial bacteria. Colonies found in your pond’s filtration system need to be sustained with flowing, oxygenated water. Switching off a filter can cause beneficial bacteria to die back during the winter months, causing them to decay instead of supporting their replenished populations come spring. These bacteria are crucial in every healthy freshwater system as they help cycle and break down potentially toxic nutrients.

The Final Verdict

It is advisable to keep one’s pond pump running all throughout winter, even during the chilliest of days. As long as water continues to run through your pump’s pipes, it should not freeze as your pond will always be slightly warmer than the air above it. Habitually switching the pump on and off, in response to dropping temperatures, can lead to worse results as this would cause the water to intermittently freeze. If you’re truly concerned about any exposed pump parts and pipes, consider wrapping them in insulating material.

Your ornamental fish and submerged plants would definitely be grateful for a continuously running pump! If you or your pump’s manufacturers insist that it should be switched off, you’ll need to provide another means by which oxygen levels can be optimized through winter. Though fish typically consume less oxygen in the cold, don’t forget that any decomposing materials and the pond’s microbiota will continue to consume it. It is therefore necessary to maintain gas exchange through the season.

Angeline L
About the author

Angeline L

I'm a passionate researcher and scuba diver with a keen interest in garden plants, marine life, and freshwater ecology. I think there’s nothing better than a day spent writing in nature. I have an academic and professional background in sustainable aquaculture, so I advocate for the responsible production of commercial fish, macroinvertebrates, and aquatic plants.

Read more about Pond Informer.

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