Relentless current, undecipherable water, educated trout and an imposing reputation make this a graduate-level destination for fly fishers.
But during the winter, when most of the river is snowcloaked and closed (or about to close) to fishing, the Madison rewards hardy anglers with high catch rates in a pair of accessible tailwaters that, if not elementary, are at least fishable.
And when the right combination of weather and fishing conditions align, the water below Hebgen and Ennis dams can be very productive, indeed.
These two tailwaters remain open the entire year, but each has physical and geographical constraints that make winter fishing an adventure.
The reach below Hebgen Dam, which extends to the head of Earthquake Lake, is often within sight of U.S. Highway 287, but so much snow falls in this canyon that it's hard to access much beyond the first half-mile of river.
The second tailwater extends from Ennis Dam down through Beartrap Canyon, a rugged, remote chute whose rapids intimidate technical floaters even in the summer.
In winter, this can be a dangerous place for anglers who push their luck.
Still, there are big and numerous trout in both of these spots, and because they're moderated by the temperate flows from dams, they stay relatively ice-free all winter, havens for river trout.
They're havens for anglers too. Much of the Madison closes to fishing at the end of February, and doesn't reopen until mid-May to protect spawning rainbows.
You wouldn't want to fish most of the river during February, anyway, because its shorelines are lined with ledge ice and where it's not iced over, the water is full of slush on days when it's cooler.
"I'm not going to call the Madison an unknown place," said Dan Hurzeler at Fin-Chasers (208-557-0333) in Idaho Falls, Idaho, who fishes the river in every season, "but it's not fished all that much in the wintertime, especially considering how good it can be."
It's hard to generalize about these fisheries.
One reward anglers who drift tiny nymphs, the other produces big fish on large streamers and even hardware.
Here's a look at each of the Madison River's tailwaters:
Hebgen Dam to Quake Lake
More accessible, more consistent and more heavily fished, especially by hard-core fly anglers, this tailwater can actually host some winter insect hatches.
They're bound to be midges, and they'll appear on relatively warm, cloudy afternoons, but dry-fly fishing with size 20 and 22 is possible here.
Get here by driving U.S. Highway 287 north from West Yellowstone or south from Ennis, Mont.
If you're coming from the south, drive past frozen Hebgen Lake, wave at the ice anglers, and start slowing down as you pass Hebgen Dam.
You can access the tailwater soon after the river re-emerges from the base of the dam and the mouth of Cabin Creek.
Parking is limited, especially after one of the frequent snowstorms in the area, but you'll probably see other vehicles and other anglers, and it's worth following suit to avoid getting hit by a vehicle or snowplow.
You can fish from the area below the dam all the way downstream to the head of Quake Lake, but if you roam far, bring snowshoes and a long walking stick.
You'll buck drifts the lower you go, and it can be hard to find the river under 10 feet of snow.
Flows are hovering around 850 cfs, enough to keep the ice off the upper mile of river below Hebgen, but not enough to keep it ice-free downstream of Beaver Creek.
But where you find open water, you should find trout, mostly rainbows but a few larger browns and a growing number of 12-inch cutthroats.
The fish will be hunkered down behind rocks, along deeper banks and small holes, wherever they can get out of the current and save their energy.
They're unlikely to dart out to grab a big Bugger, but they will respond to stonefly nymphs, said Hurzeler.
"A lot of guys use micro nymphs below Hebgen, but I have good luck on larger stonefly imitations, anything dark with rubber legs," he said.
Hurzeler ties a number of his own patterns, variations on the basic Yuk Bug theme. He likes orange and red with black hackles and legs.
Other good patterns here include San Juan Worms in orange, rust, red and black, Girdle Bugs, black and brown Woolly Buggers, and every large wet pattern should be trailed by a smaller beadhead nymphs.
The hands-down favorite is a Pheasant Tail in sizes 18 or 20, but Copper Johns, Hare's Ears and Prince nymphs all get a nod.
Steve Summerhill at The River's Edge Fly Shop in Bozeman likes bigger stonefly nymphs, including Kaufmann's and Golden Stones in sizes 4 and 6 and standard baetis nymphs, but he adds Brassies in sizes 14 to 18.
"There is still some good fishing to be had, particularly in the upper reaches of the river," he said.
"The nymphing has been good along the fast edges of the big runs and in the eddies behind bigger rocks."
Ennis Dam to Beartrap
This lower tailwater is a little harder to access, but if you're hunting a big fish, this is the better spot.
Take the Ennis Lake Road east off Highway 287 right in the crossroads town of McAllister and drive about 3 miles to the dam.
You'll have to park at the designated area and hike downstream, but the fishing can be good right off the parking area.
This is big-pattern water if you're fly fishing. Go with big Zonkers, Woolly Buggers, Muddler Minnows and Sculpins.
Other effective patterns are Glo Bugs, big stonefly nymphs and big San Juan Worms.
It's also a good spot to soak baits such as nightcrawlers and spawn sacks or to cast Countdown Rapalas, smaller Lucky Craft Pointer Minnows and Yozuri crankbaits or spoons and spinners.
The trick is getting deep in slower water where rainbow and brown trout to 8 pounds lurk. Flows should be in the 1,300 cfs range.
You may encounter a midge hatch, said a staffer at Madison River Outfitters (406-646-9644) in West Yellowstone, but "Zonkers and sculpins are taking larger fish off the banks."
And Summerhill reports that "it's not been pretty, but eggs and worms have been the ticket to the fish on the lower Madison," and he recommends San Juan Worms crayfish patterns and JJ Special streamers.
There's a foot trail along the eastern side of the river through the canyon, but the lower you go in the 6 miles down toward Beartrap, the slower the fishing until you exit the canyon and find fish holding in deeper, better defined holes.
Problem is, the river below the canyon is prone to icing and the ledge ice along the shore can be treacherous.
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