Despite all the new articles about how wildlife is suffering in this cold weather new research has shown that pond life may actually be doing the opposite and benefiting.
It has generally been thought that if a garden pond has frozen over in cold weather then the best thing to do is to break a hole in the ice to allow oxygen to get in. The charity Pond Conservation's latest research shows that actually the opposite may be true and leaving the ice in place will not reduce oxygen levels, and in some cases they may actually increase. If a pond has clear water and enough pond weed then it seems that left alone oxygen levels may naturally rise, increasing the amount for wildlife living below the surface.
According to their press release you do need to take some action though if your pond has a large amount of sediment or leaves at the bottom and you also have fish in the pond. These fish will require oxygen, and so not only is a hole in the ice required, but the water needs to be agitated in some way so that the deoxygenated water keeps coming into contact with the air (as the natural diffusion of oxygen through water is to slow to take effect fast enough). A pond pump or fountain will do this, but a low tech solution is just to stir the water with a stick.
One final message is that even if you decide to leave the ice covering in place, you should ensure that you carefully remove any snow that is on top of the ice. This is quite simply because lying snow will block sunlight from getting to the plants in the pond and hence they will be unable to produce oxygen.