Caenis.
When the fish are taking caenis you fish a black marabou - did I tell you good the black marabou is? Fish it fast just below the surface and you won't fail. Usually.
Sometimes, however, it doesn't work. Important information like that is why I'm here. Then you'll need one of these.
Tying instructions:
size 18 hook, grey thread, grizzle tails, angel dubbing, grizzle hackle.