We have a carpet of algae on the sides and bottom of our pond 24/7 365 days of the year it makes the pond sides and bottom more natural looking especialy in a formal koi pond where aquatic plants are banned .
Think of your algae as a good algae what you dont want to see is string algae thars a pain that alot of folks on this site seem to suffer from each spring ( never had a problem with it as it doesnt afflict our pond which I believe is caused by exessive nutients in the water .
As John says think of it as a natural water purifier and learn to work with it. and keep it on the sides of your pond
Well it seems no-one answered the question... I too got a LOT of algae on the walls this past Winter and it was a problem this Spring as it died off and clogged up my pump half a dozen times, maybe more. I'm not exactly sure how to solve the problem. Ensuring the pond is very clear of debris like leaves before Winter should help. I did not do a good job cleaning mine before last Winter. It would also be a good idea to keep an eye on phosphate levels, as although it isn't harmful to fish, plants to consider it food.
Desilplower make sure both your pond and filters are cleaned prior to the winter the less nutrients in the water the less algae.
If possible do as we do wuth waterchanges throughout the winter months using the trickle method , it may take time but the water trickling into your pond is warmed by the ambient temperature of the pond as I've said before in other threads we never suffer the effects of algae die offs clogged drains nor string algae or green water
Dave