There are several ways to prepare to winterize your pond -- it's best to start these in the fall, so that you have time to prepare before the first freeze. Start off by insulating the walls of the above-ground pond, if possible, either by adding it when the pond is built, or by covering the exposed walls with an insulating blanket or two. Take precautions to shield your pond from prevailing winds, as well. As the temperature drops, keep a small area of the pond's surface clear of ice by using a de-icer or occasionally pouring hot water over it so gas-exchange can take place. Aside from the that one clear spot, allow snow and ice to remain on the rest of the surface. It will actually insulate the pond, keeping water at the depths warmer than water at the surface.
Most other typical winterizing activities also apply for an above ground pond. Doing a fall cleanout, removing and storing equipment like the pump, your biofilter and the skimmer. Plan on keeping an eye on your pond throughout the winter - preferably on a daily basis. If cold hardy fish are in residence, make sure that hole in the ice is maintained, and keep an eye on your water level - leaks can happen at any time, and you want to identify an issue long before it becomes a disaster.
