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.
Side note: The fishing this year and last on the Au Sable has been brutal! We aren't sure if the last two winters have killed off fish, or what's going on, but it is noticeable to me and others up that way that get to visit the river more than I do...? There were some minus 30 below nights up there in February this year!