a lake is a great idea 
my biggest question is, should the warm air in an air-conditioned room be led outside (then you have negative pressure) or should you leave everything in a closed room and hope the air-conditioning system can handle it to cool down the warm air?
my biggest question is, should the warm air in an air-conditioned room be led outside (then you have negative pressure) or should you leave everything in a closed room and hope the air-conditioning system can handle it to cool down the warm air?
Depending on the set up, you could be confronted with humidity issues from condensation which could damage your miners. In a closed environment, I imagine the air conditioning system would have to work harder (higher electrical bill). Both sides seem to have their own cons.
The same principle of heat transfer should work for any large enough body of water relative to your rig size. Not that I have any practical experience in hydro mining.