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 think this is a pretty early instar Ameletus nymph. It's certainly a striking one.
This mayfly was collected from Mongaup Creek in New York on May 6th, 2007 and added to Troutnut.com by Troutnut on May 18th, 2007.