I've seen plenty of lakes that are perfectly clear in Colorado. But.....they are all at or above timberline. If you look closely at this pic, you can see the incredible water clarity. This lake is probably 60 to 80 feet deep.
My quest is to find a lake like this one that is at least accessible with 4x4 and is sitting at less than 10,000 feet.
As far as hot springs go, the spring itself doesn't need to be dug out. The big dig could take place near the spring and warm water could be piped in. Imagine if Glenwood Springs was just 20 feet deeper.
There are more springs in the Glenwood area, Pagosa, Durango, Ouray, Ridgeway, Salida, Buena Vista, Redstone, Wolf Creek, San Louis Valley, Idaho Springs, Steamboat Springs, Radium, Wuanita Hot Springs just outside of Gunnison, Powderhorn, etc.
http://waterknowledge.colostate.edu/geotherm.htm
The development of a competitive warm water dive site in Colorado simply requires money. If anyone has a spare few million dollars lying around, they could start a sweet minimum wage business for themselves!
Wuanita Hot Springs Ranch is for sale. Its an historic hotel, dude ranch, working ranch, beautiful property. It has a main pool and many smaller private hot tubs near private cabins and if someone had enough money to buy it, they would have the right to divert the spring water into a a deep diveable pond.
http://www.waunitasprings.com/hot springs.htm
http://www.waunita.com/lodgingMeals/pool.html
The northern Colorado warm water dive training center could be a go tomorrow if the funds were there.