A faithful vistor to Trout University ask that question recently and here is my reply. We at troutu will have a class by Tom Rosenbauer, Orvis author and director of Orvis Rod & Reels, on how to quickly determine if a trout stream is fertile or infertile.
Basically, in the infertile streams like Anthony, you could use any dry fly like the yellow hammer or black ant. Since the stream is infertile, the trout are hungry and can not afford to be highly selective. For the brookies, they prefer a flash of bright orange color which is something that they can not resist, according to Dave Whitlock in Trout Unlimited magazine.
For the fertile streams with larger trout, and I suspect that Abrams will fit into this catagory, you should check with the hatch chart for Tennessee to help you in determining what fly to use; and if possible match the hatch. However, in general smaller flies are more effective in fertile streams, and I don't know why, so I would start with size 16 or less, black caddis, hendrickson or March brown. When you arrive in Townsend, please check in with Little River Outfitters. To learn more about Little River Outfitters, to to Trout University Friends scroll down to Little River Outfitters.