Trout in spring creeks and tailwaters can get very selective as to what they are willing to eat, especially when they are sipping on emergers and cripples in the surface film - this pattern works when the fishing gets "technical". Tied with a Cul de Canard (CDC) overwing and a Z-Lon underwing for a bit of flash, even the most picky trout have trouble passing this fly up. In sizes 14, 16, 18 & 20.
TIP I: These flies can be hard to see. Try fishing them in a double-dry rig behind a larger Parachute Adams or Hare's Ear.
TIP II: With any CDC dry fly, you need to use the correct floatant. Consider using either of the Shimazaki products, Loon Top Ride or Easy Dry. Don't use Aquel or Gink!