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'm unsure which species this is: it lacks the usual features of B. laurentina, but it's small, so maybe it's just an underdeveloped early instar. Otherwise, it looks like it might be B. obesa.
This mayfly was collected from unknown in Wisconsin on January 14th, 2004 and added to Troutnut.com by Troutnut on January 25th, 2006.