how does this happen?

i was just vacationing in pagosa springs. its probably one of the coolest hot springs ive ever been too, but one little thing had me entirely stumped because in the middle of the springs is a large pond that you walk over on an underwater walkway, the pond is directly connected to the spring and is probably between 85-95 degrees in temperature. yet i looked in the pond and it is virtually overflowing with koi and other large pond fish, all of which are normally considered cold water. How does this happen? i know even tropical fish usually cant stand temperatures like that long term and these fish were obviously thriving.

 

Koi are just fancy carp and, as you may know, carp can live just about anywhere.

 

okay that makes a bit of sense, i asked on of the workers there and he said they also had a large variety of goldfish, as well as some fish they called a gold orfe. not sure about these other fish.

also being a spring wouldnt the water be absolutely full of minerals making it a little saltier than average?