How can I protect koi fish in cold winter ponds effectively?

Protect koi fish in cold winter ponds by maintaining oxygen flow with an aerator and using a floating de-icer to keep a hole in the ice for gas exchange. Avoid overfeeding koi as metabolism slows in cold temperatures. Ensure the pond is at least two feet deep so fish can retreat to warmer layers. These steps reduce stress and prevent suffocation, promoting koi survival during harsh winter months.