Cutt numbers in this southeastern Idaho River seem to be creeping upward, and you can participate in this revival by drifting a high-riding grasshopper imitation along the grassy bank of the South Fork.
Chances are about even, depending on which reach of river you fish that you'll catch a scrappy Yellowstone cutthroat. And while that may not sound remarkable, consider the depths from which these fish have come.
Yellowstone cutts are native to this big river that flows out of Yellowstone National Park, through Jackson Hole entering Idaho at Palisades Dam. But over the last century or so, non-native rainbow and brown trout have been stocked in the river.
The result has been competition with the cutts for food and space.
Interbreeding with the rainbows has diluted the genetics of the cutthroats. The decline of pure-strain cutthroats was so bad that about five years ago, biologists proposed a rainbow eradication plan that was intensely controversial at first but appears to be working.
Possibly the most controversial piece of the cutthroat recovery program was the removal of limits on rainbow trout and Idaho Fish and Game's encouragement that anglers harvest rainbows.
Meanwhile, fishing for cutthroats was restricted to catch-and-release. The relatively abrupt devaluation of the rainbows was an insult to many anglers who wanted to release rainbows, which comprised about 80 percent of the river's trout.
The other part of the cutthroat program was a springtime flush of the river to disrupt rainbow spawning, and Dan Hurzeler at Fin-Chasers in Idaho Falls (see sidebar) said this operation has yielded some unintended consequences on the South Fork.
"There's all kinds of fresh habitat on the river this year," said Hurzeler.
"I haven't seen anything like this since the flooding of 1997. The riffles seem to be refreshed, and I think it's because of the springtime flush. That and the cooler weather this spring and the higher flows from spring runoff."
Refreshed riffles means better fish-holding habitat, especially during the sweltering dog days of August, when oxygen levels are low and water temperatures high. It also means abundant aquatic insect activity.
Hurzeler said he's seeing strong hatches of golden stoneflies, pale morning duns, increasingly strong caddis activity and a "mystery bug" that looks like a miniature version of a March brown.
"It's got me scratching my head," said Hurzeler.
"It's definitely a mayfly in about size 16. A mahogany dun is close, but this bug isn't as red and it has more yellowish tan on its underbelly than an Adams."
Whatever the insect, Hurzeler said trout on the South Fork from Byington Bridge to Lorenzo are keying on both the nymph and adult stages of the bug. And he said anglers who float this remote stretch of river can expect great fishing both in the riffles and along grassy banks, where they're picking off windblown grasshoppers.
"I expect the South Fork to pick up once these flows are stabilized," he said.
"There will be some great riffle action through August for guys who want to drift nymphs and smaller dry flies. It can be frustrating. You're going to see some huge cutthroats, but they don't act like cutts. They're pretty selective, so you may have to spend some time figuring out what they're eating."
What to fish
There are some shortcuts to this entomological exercise. You can bump a maroon or rust-colored San Juan Worm along the riffled water and the tail-outs of holes. Or you can systematically work the water with a smaller beadhead stonefly nymph such as a Yuk Bug in size 10 or a Montana Stone in size 8 or 10.
Hurzeler likes quarter casting upstream over a riffle and drifting a pattern downstream, being sure to keep his fly line behind the imitation.
Or you can simply float a big, brushy grasshopper anywhere on the lower river.
Hoppers will work in the Swan Valley stretch of the South Fork, but they're even more effective in the canyon stretch, from about Byington Park or Heise Bridge downstream to Lorenzo and the Highway 20 bridge or even farther down to the confluence with the Henry's Fork just upstream from Menan Buttes anglers' access.
Hopper fishing is best on windy days when the surface of the water is riffled, and trout are expecting riverside hoppers to be blown onto the water.
Good patterns are traditional Dave's and Joe's Hoppers, Parachute Hoppers and Foam Hoppers, but Chernobyl Ants, Club Sandwiches and other big, buoyant patterns will work, too.
To double your success, drop a nymph off the hook of your hopper pattern and use the big dry fly as a strike indicator.
Don't neglect hardware fishing. Big, bruiser brown trout lurk in the lower river, and Hurzeler said fishing at twilight with a silver-flash Yo-Zuri body bait is a good big-fish tactic.
Spin-fishers who cast flutter spoons just upriver and let them hang in the current on the swing often pick up nice fish.
Spinners such as red-and-yellow and black-and-yellow Panther Martins do well on larger trout. And bait is another big-fish tactic.
Dunk 'crawlers anywhere on the river or drift dead minnows through deeper lower-river pools for a shot at brown trout to 8 pounds.
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