Your dry fly drifts over a trout’s feeding station and he rises to take. At the very last instant he turns away and refuses it. Quite possibly, drag set in at the last moment and your fly developed an unnatural drift.
Any time I suspect there are unnatural stream currents around a trout’s feeding station or in the general area I plan to fish with a dry fly, I use slack line cast. This is a presentation cast that throws slack line into the leader and possibly the forward part of the fly line. I use this type of presentation in probably three-fourths of my delivery casts whenever I’m just covering the water with dry flies.
Puddle Cast
I use the puddle slack line cast most.On my presentation cast I extend about 10 feet more line than I need to reach the target. I stop the forward motion of the fly rod at a forty-five degree angle over the stream. This permits the leader and forward part of the fly line to fall in a puddle. This prevents the leader from pulling the line on the stream thus permitting the dry fly to drift naturally.
Lazy S Cast
A second slack line cast which I use is the Lazy-S cast. This is produced by wiggling the fly rod from side to side as the fly line turns over on the forward presentation cast. The slack line which results on the stream from this cast permits the dry fly to drift naturally prompting a solid strike by the trout.
The more you use these casts you will be amazed at the amount of control you will achieve with them.
For example, last year I found a large brook trout high in a remote stream in the Blue Ridge Mountains. The first three times I fished that stream I raised the trout to a dry Mr. Rapidan Parachute size 16. In each case just as the trout was about to take my fly the rapid current in the tail of the pool grabbed the line. This caused the fly to drag and the trout refused the fly.
This was a long flat narrow pool with steep rock ledges extending straight up on each side of the pool. The only way I could approach the pool was from straight below it. The only feeding station was in the head of the pool. The fourth time I fished this stream I paused well below this pool and watched it closely for a time. My trout was on his feeding station in the head of the pool coming up regularly. I crawled in downstream of the lip of the pool and made a puddle cast dropping my Mr. Rapidan Parachute size 16 two feet upstream of his feeding station. It drifted naturally to him and he took it solidly. I released him gently back to his pool and watched him as he raced back upstream.