Tiny Baetis mayflies are perhaps the most commonly encountered and imitated by anglers on all American trout streams due to their great abundance, widespread distribution, and trout-friendly emergence habits.
I didn't find a male spinner to associate with this one; I'm tentatively calling it grandis based on size alone. I found it floating down the surface of the Henry's Fork (the only one I saw that day, weeks after the hatch probably peaked) crippled by what appears to be a mass of eggs sticking out of its abdomen.
This mayfly was collected from the Henry's Fork of the Snake River in Idaho on August 1st, 2020 and added to Troutnut.com by Troutnut on August 18th, 2020.