I believe that printed briefs for or against up or down stream fishing with the fly are wearisome to the average well-read and experienced angler; wherefore brevity in discussing this point seems advisable. As regards wet fly fishing any broad-minded angler willingly concedes that under certain conditions it is best to fish the stream up and under other conditions to fish down. The dry fly man, however, has no option in the matter; regardless of all other factors for upstream fishing, the practical fact remains that the floating fly cannot be fished downstream for when thus cast it is drowned almost at once.
But even if this were not the case the application of the rule of exact imitation of nature upon which dry fly fishing is based would prove the method of casting downstream and pulling the fly up against the trend of the current wholly wrong. Even the wet fly should never be fished in this way. Parenthetically, the present writer has always recognized a distinction between fishing downstream and casting downstream; the progress of the angler may be with the direction of the current--always most advantageous upon the swift and rocky mountain trout stream--while the actual casting may be cross-current, a very effective way of fishing the wet fly under normal conditions, or upstream and slightly across if desirable. When upon the water the natural insect floats downstream as the current directs it; wherefore, as invariably as may be, the dry fly caster should cast upstream, allowing the fly to float down toward him without restraint from the line, following the natural trend of the current.
Leaving aside for later discussion the matter of drag, a state of affairs wherein the artificial fly tends to travel at an unnatural rate due to conflicting currents in the stream which affect line and fly differently, and also passing over for the moment certain other points more or less intimately connected with the advisability of upstream casting, there remains for present consideration the matter of false casting, or drying the fly.
As a rule, when casting a fair amount of line, the fly will be quite free from moisture--if previously well-waterproofed--when the angler has again lengthened out his line after having made a cast and allowed the fly to float down over the water he desired to cover. Unless the fly has become thoroughly soaked four or five false casts are enough. These should be made as gently as possible to avoid whipping the fly; the constant casting tends to shred the wings, and if this results the fly loses much of its natural appearance and is more difficult to cock.