Is it legal to fish with a barbed hook on the Southfork of the Clearwater River for trout during Salmon/Steelhead season?

Yes, page 14 in the fishing regulations only restricts fishing to single point barbless hooks while fishing for salmon and steelhead.  Barbed hooks are allowed while fishing for trout, although cutthroat are catch and release only; and if you caught a salmon or steelhead while using a barbed hook they could not be reduced to possession.  Good Luck fishing