Despite the very low temperatures, any fish should have been fine. They will go to the bottom of the pond where temperatures are a litte warmer and should come to no harm as long as some gaps remain in the ice for gases to escape. After more than 2-3 days they may begin to suffer from the effects of toxic gases resulting from rotting vegetation so do try to make some air holes. You can do this by gently melting the ice in patches with a pan of hot water. Never crack the ice by hitting it as the reverberation from this will shock the fish.
A heavily frozen pond may also suffer cracking to the structure itself, particularly if it is concrete lined. Floating a ball or two on the pond may help to keep an open hole and avoid a cracked pond.
Keeping some of the pond ice-free also helps the wild birds which will be looking for water. We had a very disgruntled pheasant pacing around our pond recently. He stopped every few steps to peck at the surface, found that is was frozen and was not at all pleased!
If you have a bird bath to provide water for birds you may like to try Ice Free for Bird Baths which stops the water freezing to temperatures down to -4 degrees C.
You'll probably find that the ice has caused any remaining lily leaves in the pond to rot, or may even have pulled the lilies out of their baskets, so as soon as the weather warms up try to tidy them up and remove any remaining leaf and stem material so that they don't add to the organic matter building up in the pond. A pair of pond gloves helps to make this job less unpleasant! If you find lumps of ice containing blanket weed or duckweed, take the opportunity to get rid of them by throwing the ice straight onto the compost heap.
And finally, whilst there is really very little that you can do in the garden, now's the time to start thinking about changes or additions to your pond for the new season. Why not try some new plants to give it a fresh appearance, even just a few new marginals. Waterside Nurseries has won numerous awards for their displays at RHS Flower Shows and has a wide range of aquatic plants which you can browse on their website.
