I have wondered if you could circulate the pond water down into the ground deeply like a well and bring it back up again the way geothermal heat exchanges heat homes or cool them. It looks to me like the energy spent would only be that of overcoming the friction in the pipes of the underground exchange system as the hydraulic pressure of the fluid column going down would offset the pressure needed to pump the water back up. Anyone know if this has been tried?

Layton Runkle