Re: What to do when....
As your nymph is ascending toward the surface it looks like a bug hatching to the trout, so at times the fish will feed on your nymph as it approaches the surface, although they will seem ignore the nymph as it tumbles along the bottom. In fact in nymph fishing it is always a good idea to let the fly hang at the bottom of the drift for a couple seconds to allow it to rise up off the surface, before you attempt to make the next cast. I think it was Jim Leisenring who first discovered this method of fishing to simulate the bugs that are hatching and swimming toward the surface. A really good book on nymph fishing was written by Rick Hafele called "Nymph-Fishing Rivers & Streams", well worth reading. We have all been there at one time or another, we finish a good drift, start pulling the line to bring the nymph up toward the surface to start another cast when all off a sudden we have a fish on.