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.
Masking hatch: When two types of insects are on the water simultaneously and the trout are feeding on the less noticeable one, the more prominent insect (usually brighter and/or larger but less abundant) is known as a masking hatch.
This other word references the same concept: masking hatches.