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.
This female is probably P. heteronea or P. memorialis since these are the two species collected during the last two weeks. It is interesting that the females are this very dark brown color while the males are lighter in color.
This mayfly was collected from the Touchet River in Washington on June 29th, 2011 and added to Troutnut.com by Bnewell on June 29th, 2011.