If you dig the pools/ponds into the ground it will help even out the temps.
If you only dig the ponds in half way use the excess dirt to berm around them for insulation and support.
Here 6ft down it's 72-75 degrees, I put some copper coils in the bottom of a hole and then a foot of sand on top to hold moisture, filled it back in and use this to regulate outside tank temperatures.
You can make a cheap solar water heater from pvc pipe and paint it black, or just lay some black plastic on the available water to heat it up.