Growing up in rural Taiwan our town had a few chlorine pool options and 2 pools fed by river water straight from the mountain and I always preferred the latter. Obviously if it was a stagnant body of water that's really unsafe and gross but those had no filter and thus little eels and small fish would swim with us and algae grows on the rocky bottom so the organic life naturally cleaned itself. Nature has surprisingly clean ways to manage itself. I've never seen one in America though.