In the mountains, the change is gradual as the final days of summer weather begin to tail off in mid-August. In the meadows enclosing the Henry’s Fork, vegetation withers in response to a drying sun and the first mornings of frost. With daylight arriving later and departing earlier, fishing becomes compressed into progressively shorter periods as insect activity becomes mainly concentrated between the hours of nine a.m. and seven p.m.
By early September, streamflow becomes reduced to perhaps half of peak summer levels and the surface of the river becomes largely altered by the appearance of great banks of dense aquatic vegetation.
It is the effect of low water flowing over and around the vegetation that brings complicating change to the requirements of presenting a dry fly in a manner acceptable to trout that have been pressured by several months of intense angler attention.
Adding to the complexity of increased disruption to surface currents is a lowering in the average size of insects that gain attention from the trout. At this time of year, one is just as likely to be tying on a fly smaller than size twenty as one that is larger, and a 6X tippet is generally the maximum diameter that can be counted upon to do the job.
Low water with enhanced clarity commands a leader well in excess of twelve feet if spooking a trout is to be routinely avoided. And as with a leader that must perform with a high level of efficiency, performance of the line must be considered equally when precise accuracy and control become the most prominent requirement.
Complacency in rod selection can be the kiss of death when delicacy must accompany correct fly placement in equal proportion. While a four weight is my usual choice, I will often shift to a three weight to cushion a tippet finer than 6X, especially when the target may exceed twenty inches in length. It is also my opinion that choosing economy over efficiency in a reel might be the biggest mistake that can be made when the leader is fine and the trout are large.
While certainly including the most demanding of all fishing I will do in the course of a year, the season of precision also offers the most pleasure and satisfaction. It is a time when even modest success becomes a notable achievement as the big rainbows of the Henry’s Fork hold the advantage in every element of a September battle between man and trout.