TXPW has an article this month on the top 10 swim holes (Balmorhea SP is #1 to them and its hard to argue if you haven't been its worth the trip ), Now check your best two, the article included beaches which I left off this list but if thats the ticket let everyone know

With 100's in North Dallas thinking of water is cool
For a quick film on Balmorhea visit this link
TPWD: Balmorhea State Park Videos