Tiny Baetis mayflies are perhaps the most commonly encountered and imitated by anglers on all American trout streams due to their great abundance, widespread distribution, and trout-friendly emergence habits.
Probably Baetis tricaudatus.
This mayfly was collected from the Touchet River in Washington on July 13th, 2011 and added to Troutnut.com by Bnewell on July 13th, 2011.