Lower Little (Sinks to Elbow)
Townsend Gauge: 2.5 to 3.0 feet is good- check out awa.org and find this river description for gauge number or call 1-800-238-2264 and press "3" when recorded message begins...listen for "Little River @ Maryville" for cfs reading...you want this one to be at least 1000 to go. This same recording will give you Watauga Lake at Sugar Grove reading...you want 150-300 MAX...anything above 300 you need to be with very experienced Watauga boaters.
Watauga River- 150-300 cfs MAX
Pigeon River (Powerplant to Hartford) 1200-1500 cfs optimum
can be done lower but it's not as much fun, the bigger the better...an awesome play wave on this river.
McGill...don't know, a website called "Southeastern Whitewater Conglomerate" has some info but web address is hard...ask Boatertalk people for it, they know
The Little Pigeon and Prong sections are very unlikely to be running, but that 1-800 line offers info on the Little Pigeon too...you need 1000 cfs minimum to go.
Hope this helps, you need to get "Southeastern Whitewater" by Monte Smith...a great sourcebook.