In cold weather

What can I do to help the creatures in my pond over the winter?

Snowy garden copyright Chris Monk

As the nights draw in and the temperatures drop, lots of people start to ask what they can do to look after their pond over winter. Based on the findings from our two Big Pond Thaw surveys a few years ago, we have developed a downloadable FAQ that summarises our advice.

My pond was full of frogs and tadpoles over the spring and summer: where are they now?

Frogs quite often hibernate at the bottom of ponds among the leaf litter and plants. They can tolerate very low oxygen levels but will survive only a few days if the pond becomes completely de-oxygenated. The simplest thing to do is make sure that your pond plants are getting some light and can go on producing oxygen under the ice.

If your pond is covered in snow it will be completely dark under the ice, stopping submerged plants and algae from photosynthesising and creating oxygen. Carefully sweep away as much of the snow as you can to allow the light to reach the plants.

Tadpoles also occasionally overwinter in the water when they don’t develop fully during the summer and autumn. No-one knows much about their survival chances overwinter: but it is likely that keeping the pond in generally good shape is the best thing you can do.

How will my dragonflies, water beetles, mayflies and all the other invertebrates cope with the cold weather?

Most pond wildlife will probably be fine as long as the pond doesn’t become de-oygenated completely, though many garden ponds do already have rather low oxygen levels even at the best of times.

Clearing the snow away is probably the easiest thing to do. Running a pump, if you have one, may be a good idea. This will certainly help fish, though no-one knows how it affects the rest of the pond’s wildlife.

Ultimately, good water quality, and allowing plenty of submerged plants to grow is probably the best way of making sure that your wildlife survives well overwinter.

I have goldfish, koi or other fish in my pond: how can I help them survive?

Fish keepers traditionally oxygenate their ponds in winter to help the fish. This is because we often keep more fish in small ponds than can strictly be supported by the natural processes of oxygenation and water purification. This is fine as long as you can keep the pumps or fountains running, and is helped by the fact that in winter fish have very much lower oxygen needs than in the warmer weather.

In fact goldfish are amongst the most tolerant of freshwater creatures to lack of oxygen, and can survive at least as long as frogs completely without it. However, be warned that this isn’t much more than a week or two, so under snow covered ice, they are at risk.

Take particular care with Koi carp, which are generally more delicate, partly because the carp from which they are originally bred are quite warm water fish. Koi certainly need oxygen but even if there is a good oxygen supply they may simply be too stressed by the cold weather to survive – and fish once weakened will often be killed by parasites and diseases after the cold weather eases. Koi keeping is a bit of a specialist art so look out for specific advice if you’re keeping these expensive creatures, rather than relying on our advice for native wildlife.

For fish it’s worth trying to keep some circulation going if you want to get them through the winter. Keep a bit of the ice open, run a fountain, and make sure the pump continues to work. It’s probably worth clearing snow: nobody knows for sure if this is an effective way of helping fish, but it should get a bit more oxygen into the water.

Where are my newts? Are they safe from the cold weather?

Amphibians like newts and frogs are as happy out of the water as in it during the cold weather as long as they can stay moist and safe from freezing temperatures. No British amphibians can survive freezing although there is an American frog that, remarkably, can survive being frozen solid.

Having a compost heap, or log pile in your garden – where temperatures stay above zero – can provide a perfect overwintering hideaway or hibernaculum for your amphibians. Wood that is damp, or decomposing and so has higher moisture levels is favoured, above drier wood. Amphibians prefer to hibernate in small spaces, so packing in loose soil or wood chippings will make hibernacula more attractive to them. Sometimes they will also hide under paving slabs, the garden shed or even the greenhouse, so make sure you are careful when doing any garden renovations in the winter. Newts will also occasionally overwinter in the pond as well.

Garden reptiles such as Grass Snakes, which are also pond lovers, and Slow-worms will also benefit from hibernacula, as these species also hibernate from October onwards. Possible sites include: animal burrows, rotted tree stumps and root holes, large grass tussocks, ant-hills, old walls and building foundations, piles of rubble and other debris and under large logs and fallen trees. Reptile hibernation sites almost always have a south-facing aspect, and are normally in full or partial sun.

So should I break the ice?

Breaking the ice doesn’t make much difference to the oxygen levels in your pond because oxygen diffuses into water extremely slowly. Unless you stir the water in some way, with a fountain or a pump, you’ll add very little extra oxygen.

Making an opening in the ice can help other creatures in your garden that may be grateful for an (n)ice cold drink, for example birds, foxes, hedgehogs and squirrels. It’s just possible that amphibians trapped under the ice of a de-oxygenated pond could be saved by being able to reach open water – and air. But as finding air holes probably isn’t part of their natural behaviour this may be more a kind thought on our part than a really good way of helping our animals. In fact, it’s more likely that amphibians would go looking for air holes at the very edge of the pond because this is where ice always melts first (because the land warms up more quickly than the water) – so if amphibians did go looking for oxygen, evolution would probably have pointed them towards the edge of the pond.

Is my pond going to freeze solid?

Even in this ongoing sub zero environment it is unlikely that ponds, even shallow ones, will freeze solid. In this country it’s rarely cold enough for more than 2 or 3 inches of ice to form on our garden ponds, so only the very shallowest ponds, or small container ponds, can freeze completely solid. As long as your pond creatures have undergrowth to nestle in and a good oxygen supply they should be fine.

Safety around frozen ponds.

Take care around frozen ponds, they may look solid but you should not attempt to stand on them. Clearing snow will also help keep any children playing in your garden aware that the pond is there and help alleviate the risk of them falling through the ice.

Our research on frozen ponds.
Remarkably little is known about garden ponds: the habitat they provide, what species thrive in them and how they should be managed best for wildlife. Because of this Freshwater Habitats Trust has started a programme of research on garden ponds to find out more about them. We’re doing this by a combination of in-house work and by asking people to tell us more about what makes their ponds tick and what’s living in them, with the Big Garden Pond Dip, and the spin-offs the Big Spawn Count and the Big Pond Thaw survey.

At the beginning of 2010 after receiving lots of calls from distressed garden pond owners who found dead frogs and fish in their ponds after the ice thawed, we launched our Big Pond Thaw survey. Finding out more about how people both with and without dead amphibians has helped us improve the advice about looking after ponds in cold weather.