I am wondering about the ramifications of installing a pool chiller on a small natural pond system. Basically, I am hoping to create a small cool plunge pool next to a sauna but would really prefer to avoid using any nasty chemicals and filters as needed for a pool. I am planning to do a small 7'w x12'l x8'd natural pool as the swim area, plus an addition 10'w x 12'l area to the side for the natural pool. I am mostly wondering what might happen to the vegetation if the water were to be cooled occasionally. The pond is going to be in Minnesota so the vegetation will be local and likely hearty to cold temperatures, just maybe not accustomed to irregular cold snaps in water temp. Any ideas here would be much appreciated. As a side note I am looking at just doing a small waterfall for aeration and cooling.
Thanks for any help.