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.
Although there is no key to female duns, I'm calling this dun Ephemerella excrucians because I collected several mature nymphs of that species on the same trip.
This mayfly was collected from Mystery Creek #249 in Washington on July 4th, 2020 and added to Troutnut.com by Troutnut on July 12th, 2020.