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.
CharlieSawd on Feb 26, 2009February 26th, 2009, 8:39 am EST
I think it is Oncorhynchus clarki lewisi, the westslope cutthroat. Bonni's tend to have more of a yellow hue. There are resident westslopes in north western WY, and as you said you were fishing a high mountain lake, my guess is you were in this region.