It would seem that the ideal conditions for the dry fly are somewhat as follows: A clear, smoothly flowing stream, whether fast or slow being immaterial if the surface is not too broken; the stage of water should be normal, although at the lower levels, as the season advances, everything is in favor of the dry as against the wet fly; finally, insect life should be fairly abundant on the stream and the trout feeding more or less at the surface on the natural fly.
In the early days of the season, when the stream is apt to be in flood and the water very cold and more or less discolored, the wet or sunken fly is plainly indicated. Until, with the progress of spring, air and water have grown warm, and the bright sunshine brings on the natural ephemeridae, the fish are usually ground-feeding, or feeding in mid-water, and will rise only infrequently to the fly fished upon the surface. At such times the fly caster who holds to the employment of the dry fly is doomed to disappointment.
In fact, it would seem that fly-fishing under these conditions should be done more along the lines of bass or salmon fly-fishing --not with the idea of simulating even approximately the natural insect food of the fish but rather with the purpose of exciting the trout and inducing them to strike by the use of a glittering or highly colored fly which, fished considerably beneath the surface, arouses their curiosity or anger or may be taken for a small minnow. This style of fishing with the fly is distinctly on a lower level than the correct imitation of the natural floating insect by means of the dry fly; nevertheless, in fairness to the many fishermen whose days on the stream are rare and eagerly anticipated with attendant hopes of some practical success, I cannot but advise the use of the sunken fly under the conditions named or when, at any time during the season, somewhat similar conditions prevail.
In an average season the dry fly man may confidently expect success on suitable water from about the first of May to the last days of the open time. The trout streams are now clear and at or below the normal stage of water; the temperature of the water is rising steadily; the observant fly-fisherman will note the natural ephemeridae abundant at intervals over and on the stream--and there is no sight in nature (at least from the writer's viewpoint and, I fancy, from that of all other trout fly-fishermen) more interesting or more wonderful than a good hatch of duns. With the advance of the season and the usual gradual falling of the water, conditions ever grow more and more in favor of the dry and against the wet fly.