Although Kogotus and Rickeri nymphs may be difficult or impossible to tell apart, I captured an adult Kogotus nonus specimen in the air on the same day as several of these nymphs, and they are likely the same species.
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.