For most fly fishermen this is important, because except for extremely talented casters, few upstream flingers can actually land their fly upstream of a fish without the line or butt section of leader entering the fish s cone of vision on the cast. By dropping the cast well upstream of the fish and letting the current take the fly to him, we can skate the fly a few inches left or right to get it in the correct current tongue before it enters into our quarry s view. In many situations, fish have a very narrow feeding lane that is tricky to hit when casting upstream, but with the minor adjustment allowed by the downstream approach, the teacup can be hit with relative ease. Third, the downstream approach allows true manipulation of the fly. Not all fish want a dead-drifted fly.
Some insects are pretty dog-gone active on the water.
When casting upstream, it is very difficult to twitch or shudder a fly without major disturbance to the surrounding water. With the downstream drift it is a relatively simple matter to add any amount of action to the fly. Another major advantage is that you can easily drift a fly under a sweeper with a downstream drift where the upstream approach makes this a real challenge. To fish the dry fly downstream, the most important change will come in your casting. There are several casts that will produce this effect.