On days when the mercury dips below zero, it is inevitable that the water in your pond will freeze over. If your pond is stocked with fish, then it is important that you do not just smash the ice on the surface as the shock waves may kill your fish. One idea is to place a hot pan full of hot water on the ice, to slowly melt away the ice. Alternatively, you could install a pond heater or a water feature which should prevent the water freezing over. Floating a ball on the surface of your pond will help to prevent ice forming or will at least slow down the process during very cold, prolonged spells.
A pump will improve the oxygen levels of the water which is important if your pond is stocked with fish or is home to amphibians. Make sure that your pond receives enough light by cutting back any overhanging branches from surrounding bushes and trees. Plants need light to photosynthesise and grow and this will also include the plants growing in and around your pond. Cutting back overhanging branches should also ensure that not too many leaves will fall onto the water. An abundance of leaves will settle on the bottom and will cause your pond to silt up.