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 would just like to use this specimen to point out that in many cases (or in all the cases I've seen), most true PMDs (Ephemerella excrucians) are not yellow, but olive (with a bit of a gold tinge).