I also fished the Holston yesterday (Sunday) just downstream of the dam and did pretty well for me. I only caught two trout in three hours, but they were 15 and 18 inches (both bow's), one on a zebra midge and the other on a wet fly swing. There are some absolute hog (to continue the analogy) trout in there that I guess made it through the summer (wonder how far down stream they made it?). There was a bunch of little stuff hatching and a decent caddis hatch that started around noon (little and light tan). The fish seemed to be taking emergers just below the surface, but I couldn't quite key in on what they were going for with a fly.
BTW, those trout fought like freight trains, the first time a trout has ever truly bow-ed my 5 weight over. Hopefully the fishing only heats up as the temp drops, I really enjoy the Holston.