Make a right on to the road, from the boathouse, and continue over the bridge, and it should be your first right (I believe its called Palmer Road or Drive or something).
Continue to the end of that road, and there’s and a dirt road that you follow to the campground.
That’s rough, though, I’m not sure exactly where that road is. But, you should find it pretty easily. I know that if you’re coming from the other direction (towards the boathouse from Barry’s Bay/Toronto), its the first street before the bridge.