Yes, on Watauga River if you don’t have a PFD on your boat, kayak, raft, etc., TWRA will fine you if they see you.  Best to have it ON.   The water is very cold and if you were to fall in it could be your life.   I think the fine is somewhere in the neighborhood of $265.00 +-  And if a child does not have the PFD on you may be taken to jail.     SAFE THAN SORRY Wear the PFD.