I used to have a neighbor with a gold fish pond, and large (8 inch, 20 CM) or bigger gold fish (Koi?). The pond was only about a foot deep and would often freeze over and/or freeze solid. As I recall the fish seemed to survive for years of this freeze and thaw process.

What happens when a gold fish pond freezes?


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It is unlikely that a fish pond would freeze solid and have the gold fish survive. As temperatures drop the fish enter a state of torpor (similar to hibernation). I could not find any reliable references supporting gold fish or koi surviving in a completely frozen pond.

The biggest risk to fish wintering over in frozen water is lack of oxygen. The layer of ice over the top of the pond causes the fish to suffocate. Solutions include a small heater in one corner of the pond that will keep a small area (not the whole pond) ice free and support gas exchange between the water and the air.


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    I had a little water feature that had frogs every summer. I had a little heater that would activate if the temperature got below 35 degrees F. That would allow a bit of ice on the surface, but kept an area ice free. I had frogs every year thanks to that little heater.
    – pixelmeow
    Dec 4, 2015 at 18:35

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