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.
These are very rarely called Tiny White-Winged Curses.
When the important hatches of Tricorythodes were first discovered by anglers, Caenis was given the credit. We now know that the Caenis mayflies are a different group, smaller and less common in trout streams, and they hatch in the evening instead of the morning.
They very rarely elicit selective feeding, but when they do they're very tough to match because they're often much smaller than size 28. This difficulty has earned them the nickname "Angler's Curse."