Since it never gets all that cold down here in South Texas, I haven't paid much attention to threads about frozen ice on the ponds, cold water, withholding food, turning off the falls, etc. My fish stay active and feed all winter long, if a little less than during the warmer months.
Well, the other week when the temperature dipped way cold, I realized that these concerns are valid.
It got down around freezing, and I noticed that the fish were not moving around, but huddled together like sardines at the bottom. No interest in coming up to eat when I walked out in the morning.
How on Earth could the water have gotton so cold in one night? After all, the pond is 3' deep in one end, and there's plenty of water to hold a stable temperature. Then I realized that it was the pump and water fall, exposing the water to the cold air, and then pulling it down into the bottom of the pond.
After a few days, when it warmed up again, the water warmed up also, thanks to the pump and falls, and the fish were swimming around as usual.
I'll make sure to remember this, and when it gets into the 20*'s next week, I'll shut off the falls.