Looking After A Pond In The Winter

Winter can be a challenging time for a pond, particularly one containing koi, goldfish or other ornamental pond fish. As water temperatures fall, fish become less active, biological filtration slows and prolonged freezing weather can reduce gas exchange at the pond surface.

The good news is that an established pond usually needs less intervention during winter, not more. The important things are to keep an eye on your fish, avoid sudden changes, manage pumps and filtration appropriately and make sure a fish pond does not remain completely sealed beneath ice for prolonged periods.

This guide is primarily intended for ornamental ponds containing koi, goldfish and similar pond fish. Wildlife ponds generally require less intervention and should be managed differently.

Winter Pond Care Checklist

• Check your pond, fish and equipment regularly.
• Remove excessive leaves or decaying organic material.
• Monitor the pond water temperature, rather than relying on the air temperature.
• Reduce feeding as the water cools.
• For koi and goldfish, consider stopping feeding when the water falls below approximately 8°C.
• If your pond pump continues to run, consider raising it away from the deepest part of the pond.
• Check exposed pipework, filters and UV clarifiers during freezing weather.
• Avoid waterfalls and fountains if they are causing excessive cooling.
• Prevent a fish pond from remaining completely sealed beneath ice for prolonged periods.
• Never smash or crack pond ice.
• Continue to observe your fish for unusual behaviour or signs of ill health.

If you are still preparing your pond for the colder months, see our Autumn Koi and Goldfish Pond Maintenance guide for advice on removing fallen leaves and excessive sludge, checking water quality and preparing your pond before winter arrives.

Should I Keep My Pond Pump and Filter Running in Winter?

There is no single answer for every pond. Whether your pump and filter should continue operating through winter depends on the type of equipment, pond depth and design, pipework and the manufacturer's recommendations.

In many established ornamental fish ponds, filtration can continue operating throughout winter. Keeping water circulating can help maintain oxygen levels and allows the filter system to respond as conditions change.

However, winter operation also has disadvantages. Water passing through exposed filters, pipework, waterfalls or fountains can lose heat to the colder air, while severe frost can damage equipment or cause exposed pipework to freeze.

For this reason, it is worth looking at the whole filtration system, rather than simply deciding whether the pump should be switched on or off.

If your system continues running:

• Check that exposed pipes cannot easily freeze.
• Consider bypassing waterfalls or fountains during very cold weather.
• Make sure the pump remains fully submerged.
• Check the manufacturer's winter operating instructions for your pump, filter and UV clarifier.

If you intend to shut a system down for winter, follow the manufacturer's instructions for cleaning, draining and storing any equipment that could be damaged by freezing.

Do not assume that every filter, UV clarifier or pump should either remain running or be switched off throughout winter. Different systems have different requirements.

Where Should I Position My Pond Pump in Winter?

If you intend to keep your pond pump running through winter, consider raising it from the deepest part of the pond onto a shallower shelf or suitable support.

During cold weather, fish often spend long periods in the deeper areas of a pond where water temperatures may be more stable. A pump positioned at the deepest point can increase mixing between this deeper water and colder water nearer the surface.

Raising the pump can help reduce this mixing while still providing useful circulation.

The pump must remain fully submerged and should always be positioned in accordance with the manufacturer's instructions.

This is particularly worth considering in deeper koi and goldfish ponds. Every pond is different, however, so pond depth, pump flow rate, return position and filtration layout all need to be taken into account.

Should I Run a Waterfall or Fountain During Winter?

A waterfall or fountain can provide useful circulation and aeration, but during cold weather it can also expose a large amount of water to cold air and increase heat loss.

If you have a separate waterfall or fountain, you may therefore decide to switch it off or bypass it during prolonged cold weather while continuing to operate the main filtration system.

Whether this is appropriate depends on how your pond is designed. In some installations, the waterfall forms part of the main filtration return and cannot simply be switched off without making other changes.

Always make sure any pipework or equipment that is taken out of service is protected from frost damage.

What Should I Do If My Pond Freezes?

If a pond containing fish freezes over, do not smash or crack the ice. The resulting shock waves can harm fish.

Instead, aim to maintain or gently create an ice-free area.

• A floating pond heater or ice vent.
• A suitable pond air pump.
• Water movement from an appropriately positioned pump.
• A purpose-designed floating device.
• Gently melting an opening by holding a pan containing hot water against the ice.

We currently stock winter accessories, including pond thermometers and ice vents, in our Other Pond Accessories range.

Do not pour boiling water directly onto your fish or into the pond.

RHS guidance recommends taking action when a fish pond freezes because oxygen levels can fall beneath prolonged ice cover. It also specifically advises against smashing the ice.

An ice-free area also allows gases produced by natural decomposition within the pond to escape.

Does the Whole Pond Need to Be Ice-Free?

No. You do not need to heat the entire pond or keep the whole surface clear.

The objective is normally to maintain sufficient gas exchange rather than trying to prevent every part of the pond from freezing.

In very cold weather, check the pond regularly because an opening created one day can freeze over again.

Can I Cover My Pond to Help Prevent Freezing?

Covering part of a pond can help reduce heat loss during severe weather, provided it is done safely and does not completely seal the pond.

A sturdy frame can be used to support suitable insulating material above part of the water surface. The cover should be securely fixed and should not prevent ventilation or create a hazard around the pond.

There should still be adequate opportunity for gas exchange.

For most UK winters, it is not necessary to try to keep an ornamental pond warm. The aim is simply to reduce extreme temperature changes and protect the pond and equipment during particularly cold spells.

Should I Feed Pond Fish During Winter?

As pond water cools, the metabolism and appetite of koi and goldfish gradually decrease, so they require less food.

Use the pond water temperature, rather than daytime air temperature, when deciding whether to feed. A pond thermometer makes this much more reliable than judging conditions from the weather alone.

As temperatures fall, change to a more easily digestible wheatgerm-based pond fish food.

The Ornamental Aquatic Trade Association (OATA) advises that when the water temperature falls below approximately 8°C, it may be better not to feed koi and goldfish at all.

Do not continue feeding simply because the fish approach you at the side of the pond. Uneaten food and increased fish waste can contribute to poor water quality at a time when biological filtration is also working more slowly.

When temperatures begin to rise again in spring, feeding should be reintroduced gradually.

What About Sturgeon?

Sturgeon are an important exception.

OATA advises that sturgeon should continue to be fed throughout the year, including at lower temperatures. They also have different nutritional requirements from koi and goldfish and generally require a suitable high-protein sturgeon food.

If your pond contains sturgeon as well as other pond fish, do not apply general koi and goldfish winter feeding advice to them.

Should I Test My Pond Water During Winter?

Yes. Although fish may be less active during winter, poor water quality can still cause problems.

If fish behave unusually, testing your pond water should be one of your first checks.

For an ornamental koi or goldfish pond, useful tests include:

• Ammonia.
• Nitrite.
• pH.
• Nitrate where appropriate.

Ammonia and nitrite should both be zero.

Problems can arise from uneaten food, fish waste, decomposing organic material or filtration that is no longer working effectively.

Winter is not a reason to ignore water quality simply because the fish are feeding less.

What Should I Look for in My Fish During Winter?

It is normal for koi and goldfish to become less active as the water cools. They may spend long periods close to the bottom of the pond and show less interest in food.

However, continue to observe them regularly.

Look for unusual changes such as:

• Fish gasping or spending unusual amounts of time at the surface.
• Erratic swimming or loss of balance.
• Abnormal isolation from other fish.
• Excessive mucus.
• Sores, ulcers or damaged skin.
• White spots or fluffy growths.
• Unusual changes to the gills.
• Fish becoming progressively thinner or showing other changes in condition.

If fish appear unwell, check your water quality first. Poor water conditions can cause symptoms themselves and can also make fish more vulnerable to disease.

Be cautious about adding treatments to very cold water. Some pond treatments have minimum operating temperatures or work differently at low temperatures, so check the manufacturer's instructions before treating the pond.

If treatment is appropriate, our pond tests and treatments section contains water treatments and fish-health products, but if you cannot confidently identify the problem, seek advice rather than treating repeatedly for different diseases.

What Is Carp Pox?

Carp pox can become particularly noticeable on koi and other carp during colder weather.

It typically appears as smooth, pale grey or whitish wax-like patches on the skin or fins. This looks different from the fluffy or cotton-wool appearance commonly associated with some fungal problems.

Carp pox is caused by a virus and the visible lesions often become less noticeable as water temperatures rise again.

However, do not assume that every pale patch or skin lesion is carp pox. Similar-looking symptoms can have different causes. If the fish appears unwell, lesions are spreading rapidly, the gills or eyes are affected, or other fish are developing symptoms, seek specialist advice.

Do Wildlife Ponds Need the Same Winter Care?

Usually not.

A wildlife pond with few or no fish generally benefits from less intervention than a heavily stocked ornamental fish pond.

RHS guidance notes that wildlife ponds do not normally need an opening made in the ice unless there is a build-up of rotting material, as submerged plants and algae can continue to support the pond ecosystem.

Avoid unnecessarily disturbing hibernating wildlife or carrying out major pond cleaning during winter.

The advice about filtration, feeding and maintaining an ice-free area on this page is therefore primarily aimed at ornamental fish ponds.

Frequently Asked Questions About Winter Pond Care

Should I turn my pond filter off in winter?

Not automatically. Many established pond filters can continue operating during winter, but the right decision depends on the filter, pump, pipework, pond design and manufacturer's recommendations. Make sure exposed equipment is protected from freezing.

Should I turn my pond pump off in winter?

Not necessarily. A pump can provide useful circulation and oxygenation during winter. If you keep it running, consider raising it away from the deepest part of the pond so that it does not unnecessarily mix deeper water with colder surface water.

What temperature should I stop feeding koi and goldfish?

OATA advises that when pond water falls below approximately 8°C, it may be better not to feed koi and goldfish at all. Reduce feeding gradually as the water cools and use the water temperature rather than air temperature to make feeding decisions.

Should I break the ice on my pond?

No. Never smash or crack pond ice because the resulting shock waves can harm fish. Use a pond heater, air pump or suitable floating device, or gently melt an opening instead.

Does my whole pond need to remain ice-free?

No. It is normally sufficient to maintain an area where gas exchange can take place. You do not need to heat the entire pond.

Can I leave my waterfall running in winter?

Possibly, but waterfalls expose water to cold air and can increase cooling. If your pond design allows it, you may choose to bypass or switch off the waterfall during prolonged cold weather while maintaining appropriate filtration and circulation.

Do pond fish need feeding throughout winter?

Koi and goldfish usually require progressively less food as water temperatures fall and may not require feeding below approximately 8°C. Sturgeon are an important exception and should continue to be fed throughout the year.

Need More Help With Your Pond This Winter?

Winter pond care can vary considerably depending on your pond depth, fish, filtration system, pump position and the equipment you have installed.

If you are unsure whether to keep your filtration running, where to position your pump, whether your fish should still be fed or how to deal with a frozen pond, our experienced team is happy to help.

You can ask our pond experts a question online, or call us on 01778 341199 for friendly, practical advice.

Sources and Further Reading

• Royal Horticultural Society (RHS) – Pond care
  Guidance on winter pond maintenance, ice, oxygenation and wildlife ponds.
• Ornamental Aquatic Trade Association (OATA) – How to Look After Pond Fish
  Guidance on seasonal feeding, the approximately 8°C feeding threshold, sturgeon and general pond-fish care.

Last reviewed: September 2026

Water Gardening Direct has supplied pond equipment and provided practical pond care advice to UK pond keepers for over 25 years.