Rene Harrop with a nice cutthroat caught during a baetis hatch.

The fish are feeding in 18 inches of water on the inside edge of a deep slot that provides instant security from anything threatening. One careless move on my part and they would vanish into deep water. The downstream fish is not the largest of the three, but it is nearest to my position. A cast to the bigger target means casting over the closer fish, and the result would be predictable. The water appears nearly black against the ashen sky, and the small mayflies that pepper the surface are indistinct through my snow-spattered glasses. Wiping them on the collar of my fleece jacket helps to some degree, but close inspection is not necessary. It is Baetis time. In these conditions it's not likely any other mayfly would appear on the water. I have been here before on many occasions over the years, and the #22 emerger is already knotted to the 7X tippet.

Baetis nymph.

A narrow drift line where quick and slow water meet collects scores of the tiny olive insects, and the fish I've targeted pushes eagerly against the food-laden seam. A perfect cast will place the fly six inches above the rise, and a perfect drift will match the feeding rhythm. Two inches right or left will take it off line and out of the zone of acceptance. If I see the fly, it will be because drag has pushed it across the surface at a speed completely unlike the naturals. Only the absence of wind makes the situation seem even remotely possible. Even then it will take more than a little luck. You cast more by feel at times like this, but somehow you instinctively know when the presentation is right. And that is how it went when the third cast just felt good, and the trout rose exactly when I sensed the fly was where it should be. I tightened to solid unyielding weight, and the trout plunged into heavy water.

Baetis Nymph

Hook: #18-22 Tiemco 200R BL. Thread: Olive 8/0. Tail: Wood-duck flank. Rib: White Super Hair. Body: Rusty olive dubbing. Wingcase: Black marabou. Legs: Brown Hungarian partridge.

Beyond the channel lies more than a hundred feet of open water, but in this season it is less than a foot deep. Reluctant to leave the safety of a deeper flow, the big rainbow thrashed briefly on the surface against the sting of the tiny hook before diving toward the bottom to slug it out. Heavier than the 2 1/2-pound breaking point of the tippet, the fish is in total command. Only its refusal to charge recklessly across the shallows gives any hope of prevailing. But in the chilled water of winter-like conditions, the rainbow does not exhibit the violent resistance typically associated with its species. Turning its head with lateral pressure, I force the fish to fight the current more than the rod, and it begins to tire. Instead of lifting this heavy fish, I lead it slowly toward the near bank by keeping the rod low and parallel to the shoreline. With gentle but constant pressure, I bring the fish into thin water where it loses all advantage of current or depth. Still, a forceful shake of the head or a quick surge against the rod would easily fracture the precarious connection. With depth inadequate to maneuver a net, I cradle the broad body against my lower leg and slide the rod onto the ice at the water's edge. Keeping the muscular rainbow mostly submerged, I pluck the little olive fly from the upper jaw then guide the pulsing body into deeper water. For half a minute I admire the magnificence of an autumn rainbow, then watch it disappear effortlessly into the water.

Bonnie Harrop caught this 23-inch hen rainbow on 6X and a #22 Baetis dry fly in October on the Henry's Fork.

People commonly imagine fall as a calendar photo replete with colors symbolic of the season and bathed in warmth by a low-angled sun. At lower elevations, fall brings welcome relief from incessant heat while preserving a period of relatively comfortable weather for as long as several months.

Autumn in the high country, however, is a different story. Morning frost in late August marks the beginning of a season once described to me by a mountain-dwelling hermit, who has since passed on, as a collision between summer and winter. The wisdom of those words rings loud and clear when temperatures plunge below freezing in mid-September or on an October day when it can push 80 degrees F. Snow can come at any time, and a heavy rain can change the character of a river in a matter of hours.

One might think such varying and unpredictable extremes would discourage the pursuit of mayfly hatches and rising trout, but such is not the case. Fall, for all its vagaries, is the favored season for a relatively rare breed of angler willing to put sensibility and physical comfort aside for one last chance to feed an addiction to the dry fly. Although it would be a misrepresentation to portray autumn in the Rocky Mountain West as a tumultuous period of climatic extremes, the final days before true winter sets in, which can be as early as late October in some years, are unpredictable. Fall begins and ends early above 6,000 feet and within that brief window of late-season opportunity lie warm, golden days. Remarkably, some of the best fishing happens on the days that seem least hospitable.

Emerging Baetis.

Known commonly as Blue-winged Olives or BWOs, Baetis are among the most unusual mayflies in existence. Their vast geographic distribution and a propensity for cold weather make them uniquely suited to committed anglers who seek quality dry-fly fishing in the East and the West. Although their small size and the late-season low-water conditions complicate the picture, Baetis are a reliable attraction to trout of surprising size and numbers. It is a time for delicacy in all facets of tackle, approach, and presentation. A Baetis hatch demands your best, but in return you become a more enlightened fly fisher.

Baetis CDC Floating Nymph

Hook: #18-22 Tiemco 206 BL. Thread: Olive 8/0. Tail: Coq de Leon or wood duck. Abdomen: Olive goose biot. Thorax: Olive dubbing. Wingcase: Dark dun CDC cupped over thorax. Legs: Olive CDC fibers.

There is a special intimacy with the water when flows are low and a summer's growth of aquatic weed concentrates the fish into distinct and accessible holding areas. Things only imagined during late spring and summer are suddenly revealed in the clear and gentle currents of autumn. There is no better time to observe the life that dwells within a river, and no greater opportunity to learn the ways of trout and the life forms they depend upon for existence.

My wife Bonnie is small in stature and a nonswimmer. She is also, however, one of the most enthusiastic and determined anglers I know. The Henry's Fork, our home river, is wide but relatively shallow in the areas we prefer. Although only slightly above average in size, I roam at will in most of the water we fish together. It is a different story for Bonnie. Water that reaches my waist crowds the top of her waders, which makes it a perilous venture at times.

To her credit, Bonnie does good business during the summer fishing the shallow flats or along the edges of deeper water. But in the fall when wading ceases to be such a risky undertaking, my wife becomes a free-ranging predator. Delivered from the confines of deep, heavy currents, no trout in view is immune from her purposeful attention. Bonnie prefers an upstream presentation and stalking trout from behind. Once in position, she is relentless and I have seen her put more than an hour into an especially resistant fish.