There are many springs high in the mountains (even above 3,000 feet) that cool these streams and give us good fishing this time of year. Use your stream thermometer and watch closely for these springs. The recent rains have provided good water levels for this time of the year. I was fishing in these streams earlier this week and had some good fishing. The water temperature was 63 degrees.
I did well with a Mr. Rapidan Ant size 18 and Murray's Flying Beetle size 18 on a Classic 6X leader.
Update for September 1, 2020--With all of the extra rain we have received the bottoms of the streams in the Shenandoah National Park are too high to fish. You will do best by coming in off the Skyline Drive and fishing the headwaters until this extra water has time to run off.