In most situations, it is unneccessary to drain your pond for the winter. There’s typically no real reason to drain the water in either a fish or planted pond, as long as you winterize the pond correctly. Your pond's health may even end up improved after a good winter's nap. Firstly, check the type of fish and plants you have and consider whether they're hardy for the winters in your area. If ponds typically freeze over and form ice in your region, tropical fish and other warm-water life simply won't make it. Koi and common goldfish shouldn't have any problems, though, as they have larger fat stores and are more equipped to handle the cold weather. If you have fish sensitive to cold temperatures, move them indoors, in holding tanks or aquariums. In areas where the temps are milder and only rarely hit freezing, you may be able to keep some fish outside.
Instead of draining your pond completely, it may be worth doing a partial water change to give your pond a positive start before the winter. This will improve conditions so that waste is less quick to build up and harm your water quality. Make absolutely sure to do this before the temperatures start to fall, as recirculating or changing your pond's water in the colder months can be very hard on your fish. Water settles into very distinct layers according to temperature, with the warmest water settling at the bottom. This is where your fish will tend to hang out, but any activity that mixes these layers of water can confuse your fish or even wake them up from their dormancy.
