Just a mere 1.5 miles down the Blanco River from an access point at Bendigo Crossing (CR 178/Wayside Dr) you will find Boy Scout Lake. In the summertime, several camps operate along the river banks and would make this section of river less than enjoyable. But the spring and fall offer a peaceful trip down a beautiful piece of water with exceptionally good fishing opportunities.
Parking is not allowed anywhere near the crossing so you will need to unload quickly and find parking in the residential area just a tenth of a mile to the north. You will start out in shallow water as you head down river but it slowly gets deep enough to navigate most watercraft. There is another private drive crossing about 1/4 mile into the float that has an easy portage on its north side.
After about another 1/4 mile Boy Scout Lake begins. Expect the river to be wide, deep and slow for the next mile. Both banks offer good fishing and you will find several good swimming holes too. Enjoy the shade from overhanging cypress trees and clear cool water if its a hot day. Keep an eye out for wildlife, aside from the normal whitetail deer and waterfowl, I have even seen a few flocks of turkey along the shorelines.
Once you reach the dam, you will probably want to return upriver to Bendigo Crossing. If you choose to continue downriver, you can lower your watercraft down the dam by sliding it down the mossy concrete into a pool on the north side. The next publicly accessible pull-out will be Pioneer Crossing, about 5.3 miles down river.
For a nice photo journal of a float trip through Boy Scout Lake, check out this Flickr album: http://www.flickr.com/photos/texasriverbum/sets/72157625751856974/