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.
Key features I discerned with a microscope include that the femoral flange is blunt (again, given the other features and location, I probably misread this one), postero-lateral spines with the anterior longer, and the first gill is not extended.
This mayfly was collected from unknown in Wisconsin on February 7th, 2004 and added to Troutnut.com by Troutnut on January 25th, 2006.