Pond - Heat pump

I have a relatively small pond of 2000L or 550 UsG, and one the problems
I have is fairly large swings in temperature. I was considering using
the heat of the ground to moderate long and short term temperature
fluctuations by burying a pipe 3 feet or so underground round my garden,
and pumping the pond water through.
The idea came from methods for heating and cooling houses by a similar
method. I've tried a few web searches but not found anything relevant
yet. Has anyone come across such a scheme?

Peter