I have wondered about running a heat exchanger loop like a heat pump would have to cool a small pond. Taking in the warm top water and pumping it into the loop and then just back into the pond. If the loop is long enough and in the 53* ground you could keep the water temp year round.

One would have to calculate the thermal loss of the surface area of the pond. It would be like creating your own cold water spring.

Cheers Don.

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7/8th of an acre, Perch only pond, Ontario, Canada.