The waters south of the dam at Prairie du Sac has some navigable water for deep v style boats but not a lot.
You can basically run from the boat landing upstream to the dam or downstream to the bottom edge of Eagle island. (including the sand bar island below Eagle island)
The stretch of river from the sand bar island down to Sauk City is not what I would call navigable water in a deep v style boat.
If you launch from the boat landing just above the old railroad bridge in Sauk City, you can run upstream 1/4 mile above the old wingdam and downstream a hundred yards or so below the railroad bridge. Going below the first rock bar below the railroad bridge in a deep v style boat would not be wise.
For reference, I grew up on this stretch of the river and recently bought a jon boat just for this purpose.
As for special stickers, none needed that I’m aware of.