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.
I have been fly tying and fishing for over 30 years now. I'm grew up in SE Minnesota, and now living in Wisconsin. I know just about every rock and rapid on hundreds of miles of trout water in Houston County Minnesota. Most of the hatches and honey holes.I used to do fish taxidermy, now I build guitars.