Green Drakes are the West's summer flagship hatch. Late June through July, they emerge in late afternoon and bring the biggest fish in any river to the surface. Sizes 8–12 are huge for a mayfly — comparable to a hopper.
When they're on, fish them. The hatch is short (usually 30–60 minutes per evening) and dense. Match the size and the upright wing posture; a Green Drake Cripple or a Western Green Drake Parachute covers most takes.