Originally Posted by Hardyreels
Sorry to say but unless I were there to watch what was happening I can't begin to solve the mystery. There are many things that can cause fish to ignore a fake bug floating on the surface. My answer was always the same if I had any trouble matching the hatch, I tied on a # 18 or 20 Blue Quill. The fly was one having real mallard quill wings in slate gray and this pattern produced in every place I have ever fished with a dry fly. When I say 'every place' I mean from the Canadian Maritime Provinces across America, and I catch Grayling, trout, and char on the pattern here.
For a river like yours I would use the #20 and a 7X fluorocarbon tippet. Those fish have seen it all. Also be sure you aren't laying fly line over them or false casting right over them. Fish with people experience tend to recognize fly lines and that makes them more skeptical of something floating overhead.
best I can do from this distance,
I can't find a pattern for the Blue Quill. Do you have it?
Also, I was using size 14-16, so that could have been my problem.