Several years ago I discovered the choice feeding station for an exceptionally large brook trout high in the Blue Ridge Mountains. The hatches were over so when I saw him feeding I drifted a Mr. Rapidan Ant size 14 over him on a 6X leader and he took it solidly. I was on that same stream three weeks later so I tried again with my ant pattern. He came up and looked but refused it. Several hours later I came back and tried on a size 18 Mr. Rapidan Ant on a 7X and he took it. Over the next month I tried with the size 18 Ant, but more refusals. I switched to a Murray's Housefly size 16 on a 7X leader and he took it. Why? The silhouette of the Murray's Housefly with the spent wings was entirely different from the ant, thus showing the trout a new light pattern. Try this sometime. This could easily explain why a trout would take an Elk Hair Caddis while refusing an Adams which he sees over and over. This week I had some good fishing with the Murray's Housefly and Murray's Flying Beetle.
The streams are low and clear in the Shenandoah National Park so the trout are very wary. You will need to sneak, sneak, sneak. Try to find a stream that has a natural spring entering and fish downstream. This spring not only helps the water levels but has cooler water temperatures that the trout like on 90 degree days in the summertime. Or try to get to the stream early in the morning for cooler water temperatures as this prompts the trout to feed better.