The famous nocturnal Hex hatch of the Midwest (and a few other lucky locations) stirs to the surface mythically large brown trout that only touch streamers for the rest of the year.
This one pretty clearly keys to Kogotus, but it also looks fairly different from specimens I caught in the same creek about a month later in the year. With only one species of the genus known in Washington, I'm not sure about the answer to this ID.
This yellow drake dun hatched out of my aquarium over a month before her brethren in the wild are slated to emerge. She seems a bit small, and that might be the reason.
This is a fine specimen of one of the prettiest mayflies, Jason. She is small compared to some limestone specimens, but well within range for the species. I've collected varia males as small as 12mm, but many of the limestone females are 19-20mm. I think premature hatching is to be expected in aquaria.