Waters gonna be cold,The air aint to hot either, but I would take an extra day of to float around.
http://www.youtube.com/watch?v=2074dMBRtdg
I like that song!! Looked up the place I was thinking of and it is too far away. It is up close to Kerrvillle. The Blanco has a blue hole though and some nice floating spots. I bet the water will be cold. My swimming pool is still too cold to swim in too.