Anywhere up river of Yates Crossing (south South LLano River, Junction, etc) or around Castell would be a great starting point. Downriver of Yates Crossing is OK for a few miles, but a float from Yates to Whites Crossing is not recommended.
"Water is life's matter and matrix, mother and medium. There is no life without water." -Albert Szent-Gyorgyi
"No man ever steps in the same river twice, for it's not the same river and he's not the same man." - Heraclitus