In winter your pond will get colder and ice may form on the surface. This will sometimes be for an extended period of time depending where you live.
Your pond life has evolved to live in this winter environment. However that is not to say that a pond owner can’t help it through this time of year, especially if the winter is extremely long or harsh. Some animals such as frogs and turtles retreat to the bottom of your pond in winter. These animals hibernate in the sludge until spring comes and everything warms up. If your pond surface completely freezes light can still get through so plants can still photosynthesize. However if snow falls onto the ice and is left to blanket the pond your aquatic life will no longer have the light it needs to produce oxygen and then your pond life will die, if left to long. It is recommended to keep at least 30% of your pond’s surface snow free. Of course be safe when doing snow removal.
Another way to help your pond in the winter is to keep a hole in the ice to allow unwanted gases to escape and oxygen to enter your pond. You can do this by adding an air pump.