I was in New Braunfels several years ago in the middle of Summer. I remember that it was so hot and humid that at the Schlitterbahn water park dozens of people were just standing in the river for relief. They weren't playing, just standing there.
I also seem to remember a little lake nearby that has glass bottom boats on it where you can actually see the water kicking up the sand as the it comes up from the ground. I don't remember if that is where the Comal starts or some other river nearby.
I also remember an abandonded waterview theater on that lake where they once had had a pig who swam underwater.
Tom