You are probably thinking of Blue Lake down in Wendover. It's relatively warm due to the geothermals and can have viz up to 40ft but at times can also get pretty bad viz (the last time my wife was there is was only a few feet) with algae blooms. Surface temp is 60-70 deg with it only getting warmer as you descend. There is always Homestead Crater too which is like diving in a 30 ft deep hot tub.