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 pretty little dun was part of a sparse midsummer evening hatch on a large Catskill river.
I could not identify it by following a species key step by step, but I tentatively keyed it to the genus Nixe, and based on distribution maps and physical descriptions the most likely species is Nixeinconspicua. (Edit in 2023: this species was recently moved from Nixe into Afghanurus.)