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.
I suspect this is an Epeorus vitreus nymph. At the current instar, it's tough to make out the pair of dots on the tergites which signify that species, but with zooming and contrast enhancement they become evident.
This mayfly was collected from the Namekagon River in Wisconsin on January 13th, 2004 and added to Troutnut.com by Troutnut on January 25th, 2006.