How Far Can a Trout See??

by Fly Fisherman

It is important to study the flow and roughness of the water for another reason. In fast, broken-current water a trout can see underwater only three or four feet. In clear, quiet water he may see things under water that are twenty-five to thirty-five feet away, depending upon how deep he is swimming. This fact is very important in judging where you can safely wade without being seen by the trout; also in knowing from how far away the fish can see your fly. It isn’t safe to figure that a feeding trout will come more than a very few feet out of his way to get your fly. You must bring the fly to him, rather than expecting him to come to the fly. However, it is not wise to cast your fly directly to the spot where a trout is rising. Usually this will scare the fish and “put him down,” as the fly fisherman calls it. That means causing the trout to stop feeding. The scientific reason for this is that a trout sees with only one eye at a time, so he has no perspective. He can not tell quickly the size or closeness of a fly in the air. To a trout a fly in the air a few inches above the water may look about the same size as a fish hawk twenty feet in the air, so he gets out of there fast. That’s the way his instinct has trained him.
When the fly is floating down on the surface of the water and can be compared with the size of known objects like natural insects, then the trout can tell size and distance; he is not afraid of a naturally floating artificial fly.

These facts make it necessary for a skillful dry fly fisherman to use different lengths and fineness of leaden to fit different water conditions. For cloudy or murky waters and fast broken current, a 7 ft. leader tapered to IX (.009 in diam.) is a good choice, because the trout can’t see far in such water and this length of leader is easy to cast.
In very clear, still water the trout would see too plainly the connection between your fly and the more obvious line. Here a longer leader is needed-9 ft., 12 ft., 15 ft., 18 ft., or 20 ft. The length required depends upon how clear and how still is the water and how scary the trout. In this case the leader should be tapered down to 3X, 4X or sometimes 5X (.007 to .005 in diameter). You must fit the terminal tackle to the conditions

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