SWAN VALLEY, Idaho - The giant cottonwoods lining the fabled South Fork of the Snake River are quickly losing their golden autumn sheen, a seasonal event that might disappoint some.
For the avid fly fisherman, however, the bite in the air signifies the arrival of the river's best fishing days. On blustery, gray autumn days when early snow is pushed by a wicked easterly breeze, the South Fork's trout go on a frenzy.
Starting around the end of September and continuing through November when the upper stretch of the river closes to angling, the South Fork's fish pile on weight to combat the worst the coming winter has to offer.
For the river's native Yellowstone cutthroats and its growing population of wild rainbows, fall is when the fish are most active.
Cooler water, slower currents and the insect buffet the river offers up are all the encouragement the fish need to start feeding in earnest.
For the South Fork's burly brown trout, fall is spawning season.
The river's browns feed mostly out of aggression during the fall. It's the time of year when browns let down their guard a bit and become more susceptible to the furry, feathery imitations they've snubbed their noses at all summer.
For brown trout, food isn't at the top of the list this time of year. Any well-placed streamer could draw a jealous response from a testosterone-charged, hook-nosed fish with a little old-fashioned romance on his mind.
And, as the weather gets worse, the fishing magically gets better.
Bruce Staples, an Idaho Falls fly fisherman and author of the guidebook, "Snake River Country: Flies and Waters," prefers fishing the South Fork in the fall over any other season.
"The browns are moving, and if you're not interested in browns there are a couple of hatches that really bring the cutthroats and rainbows out."
Staples recommends fishing the river "on the crummiest days the days when you're thinking you should be inside tying flies."
For those searching for the South Forks big brown's, Staples has some advice: Streamers.
"Its like going into a cowboy bar," the avid angler says. "The biggest ones start fighting and they jump on the little ones, and the little ones jump on the minnows. Bring along streamer flies in somber colors like black, brown and dark olive, and then bring along some brighter patterns in yellow and chartreuse and see which ones are effective. You never know until you try."
Browns move upstream to ancestral spawning redds during low-light conditions. Staples recommends targeting the browns on the move early in the morning, at dusk or on gray, overcast days.
"This is the best time of year to go after the browns," Staples says. "Until the first week of November, they're on the move and getting ready to spawn."
Staples recommends casting streamers to the migrating browns as they hold at the heads and tails of pools and even in the riffles.
"They can be almost anywhere, but those are the best places to look for them," he says.
For the South Forks cutthroats and rainbows, Staples recommends dry flies, specifically Blue Wing Olive patterns in sizes 18 and 20. Also during fall, in selective stretches of the river, Mahogany Duns hatch out.
"I'll leave those locations up to the anglers to discover," Staples says, "but once you get into a Mahogany Dun hatch, don't leave. Those bugs are like candy to the trout."
During the fall, the Blue Wing Olive hatch happens almost every day, usually right around 2 p.m. The hatch can last a few minutes or few hours, depending on the weather and the water temperature. The hatches are more intense when the sky is overcast.
Blue Wing Olives will even bring cutthroats, rainbows and the rivers big mountain whitefish to the surface during a snowstorm.
Typically, the best Blue Wing Olive hatches happen in relatively calm water, back eddies or slow-moving runs. If a hatch is slow or sporadic, cutthroats and rainbows will chase big streamers, just like the rivers brown trout.
Another method Staples says is successful for rainbows and occasionally for cutthroats is to fish below a school of spawning browns.
"They're waiting for eggs to come down out of the redds," Staples says. "That's a high-protein meal for a trout, so they'll just park below the redds and wait. Some guys use egg patterns, but they're in the mood to feed, so just about anything could work."
Perhaps what makes the river so attractive in the fall is its accessibility to the footbound fisherman.
All summer long, especially in drought years when there's a big demand for downstream irrigation water, the South Fork really moves. It's a river seemingly made for drift boats.
In autumn, though, as irrigation demands subside and more attention is placed on holding water back in Palisades Reservoir, the river becomes accessible to wading anglers.
The river still packs a mighty wallop, and one wrong step can fill even the most experienced anglers waders with water and send him straight to the bottom.
For the careful angler, though, fall on the South Fork opens up a whole new world for the hardy fly fisherman.
"In my opinion, it's the best time to fish the river," Staples says. "Bar none."