Have not been here, but it looks nice and have heard good things about it:
Castaways
Here is an
HTML version of the Lake Conroe parks PDF.
Unless they have done something to stop it, the hydrilla (weed) is pretty intense in parts of Lake Conroe. I remember this from when I was a child (eons ago).
Of course, there is a Thousand trails if you do not mind taking a tour.