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.
Swisher and Richards were the first to discover important hatches of this species on a trout stream. They found it in a major Montana river and reported it in Selective Trout.
In 4 records from GBIF, adults of this species have been collected during September (75%) and August (25%).