Winter time for ponds runs from November through March. There are only a few things for you to do during this time.
Keep the water from freezing over completely. A hole 18" to 36" in diameter will work for most ponds. You can do this by removing your discharge pipe from your pump and let it bubble to the surface (you may need to lay the pump on its side and even raise it closer to the surface). You can use a high-volume air pump and air stones or air diffuser, or leave your waterfall running through the winter. You can also use an electrically heated pond deicer that will keep holes open in the ice.
If you leave your water features running through the winter, make sure you check it for freezing. They can create ice dams that will force the water out of the pond and you will have no water in the pond in no time.
There are many articles that talk about super cooling and not to run features in the winter because the cold air will cool the water to a lower temperature than the water would normally be if it were left alone. We have run a few studies comparing water features versus no water features and found the temperature difference to be negligible at all levels of the pond.
What ever you do, DO NOT strike the frozen ice of your pond with objects to break the ice. Striking the surface of the ice is no different than hitting a kettle drum to the fish underneath it. You can create significant damage to the fish if you do. If you need to make a hole pour hot water over a fixed spot and it will melt a hole in the ice and not harm the fish.
Remember an ice-covered pond left all winter will result in a bunch of dead fish when it melts.
Under no circumstances feed your fish during these months unless you are heating the water and keeping it above 40 degrees.