Jan is correct. Koi go to the bottom in winter (cold water) if there is adequate
oxygen. If they are up around the heater in winter or spring before the ice comes
off the pond it is because there is a lack of oxygen. Ingrid


Sorry to disagree , Jan - your pond fish will "hover" in the pond as close
to the heater as possible - they prefer warm water - that is why they stay
at the bottom without a heat source above them