If you see people on a river fishing for trout during winter, chances are good they’re fly anglers.

It’s not that fly anglers are tougher than the average angler, or more motivated, they’ve just figured out winter is a good time to catch fish and enjoy their sport.

Meridian fly fisherman Nate Brumley used to tuck away his fly rod after the first hard frost and get out his shotgun.

But he was on a November chukar hunt in 1983 above the South Fork of the Boise River and looked down and saw thousands of trout rising.

He returned with his fly rod a few days later and found himself surrounded by rising trout without another angler in sight. But the fish mostly ignored his flies.

That started a decades-long odyssey to learn the intricacies of winter fly fishing, which not only improved his fly fishing skills, it helped spawn his sideline business at dryflyinnovations.com.

SIMPLY COMPLICATED

Brumley is strictly a dry fly fisherman, and he quickly learned winter is a productive, yet challenging time for dry flies.

Many fly anglers struggle with matching hatches, but there’s typically only two insects that hatch during winter midges (aka chironomids) and a small mayfly called baetis (aka blue-wing olive).

That’s the simple part, but within those two insects lie multiple challenges, including timing the hatch, understanding its phases and finding rising fish.

“Winter fishing is more like hunting than fishing,” Brumley said.

Hatches that bring fish to the surface to feed are sporadic during winter, and often shortlived.

They tend to happen during the warmest parts of short winter days, so there’s no need to arrive early. Late morning or mid-afternoon is best.

The colder the weather, the shorter the window of time when hatches might occur, and they will occur only in certain parts of a river, typically the slower-moving sections.

UNMASKING THE HATCH

Although only two types of insects hatch, fish are very selective about the stages of those hatches, Brumley said.

“It’s a very, very technical time for fishing,” he said.

The first stage is the pre-emergence phase when the insect hangs just below the surface film of the water while they’re starting their swift metamorphosis from an aquatic insect to a flying one.

The second is the emergence phase when they’re just about the shed the shuck they are emerging from. This phase takes place on the surface just before the insect takes flight.

Third is the adult phase when the wings are fully formed, the shuck is gone and the insect is either getting ready for flight, or it has landed on the water.

Fish will almost exclusively favor insects in one of those phases, Brumley said. Typically, they will select whatever phase is most prevalent at the time.

If you cast to fish and get a few refusals, be ready to switch flies to imitate whatever phase fish are keying on, he said.

EXACT IMITATIONS

Rivers are typically low and clear during winter, and insects are commonly found in placid stretches, which means trout have plenty of time to examine a fly before eating it.

It’s critical to use flies that closely imitate a real insect’s in size, color and shape, Brumley said.

That means about six different patterns to match midges and baetis and all phases of their hatch cycle.

READY, AIM CAST

So you have rising fish in front of you, the right fly tied on and you’re ready to catch fish.

Now comes strategy.

There’s two things to remember, Brumley said. Fish are going to be skittish, and the clock is ticking. The hatch will be shortlived, and a fish spooked may not return to the surface.

You have to be an accurate caster. Baetis and midges are also tiny and are a small meal even for trout, so they won’t move much to eat them.

“Winter fish will not move to the fly right or left or chase something,” he said.

Brumley aims for the upstream fish in the school and makes sure he doesn’t cast over it. He casts right at the fish’s nose.

“Don’t flock shoot, and cast sparingly,” he said.

Despite the challenges, there are also rewards.

“When you get the combination of the perfect bug and the perfect cast, you will get him almost every time,” Brumley said.

Finally, beware that your success can be shortlived if you hook a fish that spooks the rest of the school and drives the rising fish off the hatch.

“Get that son of a gun out of the group as quick as you can,” he said.

ONE RECIPE FOR MANY RIVERS

Winter fishing can be tricky, Brumley said, but it also has a big upside.

When you perfect the methods for winter fishing, they will work on practically any river in Idaho and beyond.

“That’s the beauty of winter fishing,” he said. “If you have perfect matches of those bugs, you can be successful anywhere.”

GETTING DOWN

If winter dry fly fishing sounds too challenging, there are other options.

Many winter fly anglers are successful without ever tying on a dry fly. They favor wet flies, such as nymphs and streamers.

Fish feed subsurface the majority of the time. The river is like a conveyor belt of food. Trout will grab a morsel as it’s drifting by, and they are a lot less finicky about what they eat when it’s practically delivered to their mouths.

Nymph fishing is arguable easier than dry fly fishing because trout tend to be more approachable when they’re not near the surface, they will feed on a variety of things so fly selection isn’t as critical, and your casting doesn’t have to be as precise.

But there’s still an art to nymph fishing. You need to get your fly down to the fish and drifting naturally, and without the visual clues of a ring on the surface, detecting a strike can be difficult.

TWO FLIES AND AN INDICATOR

That’s the standard recipe for nymph fishing, according to Matt Brower at Idaho Angler in Boise.

You want the indicator to be up the leader about twice the depth of the water you’re fishing, which ideally should be knee-deep to waist-deep and moving about the speed of walking, Brower said.

Look for structure, such as boulders or large cobble with trenches or shelves. Fish will lay in surprisingly swift water when they have something in front that’sbreaking up the current.

Cast upstream of a trout’s holding area and let your indicator naturally drift through it. Keep your fly line upstream or even with the indicator so it’s not dragging the indicator downstream.

Fly preference is up to the angler, but most prefer contrasting flies, such as one large and heavy with a smaller one trailing it. You might also try one dark and one bright fly.

When you hook a fish, remember that spot because it’s likely a place where trout rest or feed during water. When you come back next time, there will probably be more fish there.

STREAMERS

These large wet flies prey on a trout’s appetite and aggression.

You want to give them a large, easy meal or invade their space and get them to attack the fly.

Fish these with a short, stout leader. Rising fish will often spook at the sight of line, but it doesn’t seem to bother fish that are chasing a streamer. They may be too focused on the fly to notice it.

You want your streamer to mimic an injured fish, so give it lots of erratic movement by quickly pulling a few inches of line then letting the fly settle and jerking it again.

ADAPT YOUR GAME

Winter fly fishing doesn’t differ that much from other times of year, but minor adjustments where, when and how you fish can make a big difference in your success.

If you respect the differences and adjust your strategy to the fish’s winter habits, you will find, as others have, that it’s a productive time to fish.

WINTER FISHING SPOTS

The Boise River: Our hometown river is one of the best for winter fly fishing. It’s close, convenient and has lots of trout. But they’re wary, and trying to catch them can be a humbling experience.

South Fork of the Boise River: This is a good winter fishery because Anderson Ranch Dam’s outflows keep the water at good temperatures for trout. It also has lots of large trout, and they will readily take tiny flies.

Big Wood River: The Big Wood is well known for its winter fishing, and getting to the river will be easy this year due to low snowfall. It’s a good river for nymph fishing, and you might get some midge hatches.

Owyhee River: Cross the border into Oregon and the Owyhee provides a brown trout fishing mecca.

You might find some ice in the slow-moving sections, but there’s usually open water available in the upper end near the dam. There’s a good chance of finding fish rising during a hatch, and don’t overlook streamers.

Malad River: This small, scenic and quirky river has rainbow trout that don’t quite act right. They will take basic dry fly patterns year round, even when nothing is hatching. The Malad is in the Hagerman Valley, which typically has mild winter weather.

The Payette River: This includes all forks of the Payette system, which have large schools of whitefish and some trout. These rivers are often overlooked, but they can have decent fishing during winter.

Roger Phillips: 377-6215

FLY FISHING EXPO

If you want to learn more about fly fishing from Nate Brumley and other fly fishing experts, there’s a full schedule of events at the Western Idaho Fly Fishing Expo Friday and Saturday, Jan. 13- 14, at Expo Idaho, 5610 Glenwood in Boise.

Hours are Friday from noon to 9 p.m. and Saturday 9 a.m. to 4 p.m. Admission is $5.

The expo will feature fly tyers giving demonstrations, fly fishing shops, manufacturers, guides, gear, demonstrations, a casting pond and more.

There’s a full schedule of free seminars (after paying admission to the expo), including Brumley giving tips on winter dry fly fishing at 2:30 p.m. on Friday.

For a full list of programs go to bvffexpo.com/Programs.html.