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.
This is the only Heptageniid mayfly I saw hatch on May 24, 2004, and luckily it floated right by me.
Edit: Gonzo confirmed most likely vicarium 06.21.12
This mayfly was collected from the Namekagon River in Wisconsin on May 24th, 2004 and added to Troutnut.com by Troutnut on January 25th, 2006.