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.
I'm calling this one Cinygmula just based on the general look and the fact that the genus is very common in this river. Official keys can't rule out other Heptageniidae, though.
This mayfly was collected from the South Fork Snoqualmie River in Washington on June 16th, 2018 and added to Troutnut.com by Troutnut on July 3rd, 2018.