Alpine Trout 101: Flies, Food, and Finding Fish at Treeline

This article originally appeared in the 2023 Fly Fishing Made Easy special publication of Fly Fisherman.

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On a recent backpacking trip on the Continental Divide Trail in Montana, I was reminded of the enigmatic and mysterious nature of fishing mountain lakes, and that you really “gotta go to know.” Re-routed trails, obsolete fishing reports, and hidden secrets proved again and again that flexibility is crucial when in the high country.

That goes for the trout themselves too. In my experience, mountain-lake trout can be some of the most temperamental and moody trout—especially considering they are often native cutthroat or Arctic grayling, which are often thought of as “easy” and/or “dumb.” The truth is that sometimes they just aren’t eating, within reach, or present at all. This could because the water has gotten too warm where the food is, they have recently gorged on abundant forage, avian predators are casting shadows on the water, or whatever other trigger puts them off.

But there are some tips and tricks that can give anglers an edge.

Click here for Fly Fisherman's video series on all things mountain-lake trout fishing.

Where and When

Where to look within the mountains. The biggest mountain-lake trout are often found in lakes that sit at the sub-alpine “middle elevations,” which is a relative height above sea level depending on your region. These are lakes below treeline that offer an optimal combination of long growing seasons, clean, cold water, and fertile fisheries that provide an abundance of forage food (see also “Stocked or Self-Sustaining” below).

In southwest Montana, this sweet spot is about 7,000-8,000 feet in elevation where the highest lakes are often around 9,000 feet and the valleys sit between 4,000 and 6,000 feet. These elevations will be somewhat similar in places like Utah’s Uintas and northern portions of California’s Sierra Nevada. But in places like the Tetons or Wind Rivers in Wyoming, Colorado’s Rocky Mountain National Park, or different areas of California’s Sierra Nevada, it will be commensurately higher. And in places like northwest Montana, portions of Idaho, and coastal ranges like the Cascades, these sweet spots will be at proportionately lower elevations.

Where to look within lakes. So-called prime lies are different in mountain lakes than the prime lies of creeks and rivers. The first places to check are inlets and outlets of tributaries. These are the places—similar to current seams in rivers— where the food gets “pinched” as it flows into or out of the lake.

Other things to look for are cruising fish, or trout that are swimming along the shallow shorelines looking for terrestrials that have fallen onto the surface. Take your time and plan out a cast that will plop your fly a few feet ahead of these cruisers.

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If it’s breezy, check for any bays or coves on the windward shoreline of the lake. The breeze can push water and concentrate food in these spots, providing a smorgasbord for fish.

If you don’t find fish at those places, take a lap around the lake. Scan every inch that you can. The fish will not always be actively cruising or in obvious spots. Sometimes they’re hanging out over an underwater spring or waiting to ambush hoppers under shoreline logs. Don’t assume, because you haven’t seen any, that they’re not there. (That said, sometimes they’re actually not there. See the “Stocked or Self-Sustaining” section of this article for more on that.)

And sometimes, especially in mid- or late summer, they’re just down deep in the center of the lake taking refuge from the heat of the littoral zone of the lake. At these times, just enjoy the wildness and scenery until the water cools and the fish come back around.

Timing. Fish beginnings and ends, both seasonally and daily. Some of the best fishing can be around ice-out and ice-up. While you might have to post-hole a bit, you’ll also find vacant trails and lakes, and potentially fantastic fishing. Gary LaFontaine wrote about trying to hit it right on Montana’s Ramshorn Lake because it could be so good. A very general rule of thumb in western Montana is that ice-out hits 8,500 feet around mid-June and ice-up occurs again around mid-October. (Many factors are involved that could make this different, like the volume and speed of water flowing through, localized temps, sun exposure, and natural springs.)

Regarding ice-out: Thirty-three-degree water temperatures are not always conducive to feeding trout. While it can be a bonanza, it can also be tough. There are never guarantees.

If it is high summer, try to stay overnight. Evenings and mornings provide optimal low light and cooler temperatures that spur feeding. Hot sunny afternoons can cause fish to take cover in the depths where there is not much food, and where it’s hard to get your fly.

Techniques. Some specialized techniques are sometimes used for difficult fish in alpine stillwaters that are not usually employed on moving waters.

When you find cruising fish that are tough to draw strikes from, try casting a leech or streamer to the center of the lake, draw the fly back in to maybe 10 feet of where the fish swam by, and let it sit. When you again see the cruisers getting close, start stripping to get your fly in front of the fish. This can provide what appears to be a more organic appearance of your fly, and the fish are less likely to be spooked by your cast.

Sometimes you just need to get funky. Nymph your drys. Strip nymphs like streamers. Come up with your own wacky idea—sometimes the fish need a different look and will get curious.

Employing different sinking fly lines can also be beneficial. There are many varieties available—check out the “Specialized Gear” section below for specifics.

Gary LaFontaine offers several more unusual suggestions in his book Fly Fishing the Mountain Lakes such as the “Floss Blow Line Technique” (using long rods lined with dental floss so that your dry fly “daps” and dances on surface in the wind), the “Hang-n-Bob” (a combination of his Floss Blow Line and right-angle nymphing), the “Multiple Roll” (flogging the water with three or four roll casts in a row before retrieving), and the “Yo-Yo Retrieve” (using a stripping action with a heavy sinking fly line and monofilament rather than running line to make your fly dive and bob just above the weeds). But some of these are quite odd and require extra gear you might not want to lug uphill.

Stocked or Self-Sustaining. Despite trout being native to the region, only a few lakes in the Rocky Mountains held trout before European settlers stocked them. A handful of large-ish, sub-alpine natural lakes like Mussigbrod Lake in Montana’s Anaconda Range (which is about 6,500 feet in elevation and about 105 acres) and Idaho’s Stanley Lake (about 6,500 feet and 185 acres), for example, held native cutthroats prior to European settlement. And portions of the southern Sierra Nevada held native goldens.

Try to determine if your lake is a self-sustaining fishery or if it relies on stocking. Self-sustainers often have better fishing as they are much more likely to have fish, and possibly big fish, year after year. Beyond that, self-sustaining lakes with limited natural reproduction will result in the biggest fish, if that’s what you’re looking for (see also “Where to Look within the Mountains” above). That’s because there will be fewer other fish to share the food, so each specimen can gorge. Lakes with high reproduction can have stunted fish, as the food biomass cannot keep up with the trout population. The biggest fish are found where only a few live. Usually. How to determine limited reproduction? Feeder streams that are too small for all the lake’s trout to spawn within, a limited number of inlet streams, inadequate depth to provide cold-enough water, and inadequate shallow (littoral) zone to provide the warmth to grow enough food are a few things to look for.

Mountain lakes are often stocked on a four-, six-, or eight-year cycle. Check the stocking records to see when the lake was last stocked. For example, if it was last stocked two years ago, you can expect plentiful two-year-old fish, and a few remaining larger fish from previous stockings. The older, bigger trout could be upwards of 20 inches (depending on the lake), and the two-year-olds can provide consistent action.

Regarding stocked lakes: A few summers ago, my wife and I were excited to hike to a lake in the southern Madison Range of Montana. We heard for years that it held golden trout. After hiking about 5 miles in 90-degree heat, we found a vacant pond overrun with leeches, mosquitoes, Callibaetis, and scuds. I later e-mailed the fisheries biologist, and he confirmed that this lake hadn’t held fish for a few years. Mountain lake fishing is different than fishing well-known rivers. Expecting the unexpected is a good idea, and therein lies the adventure.

Golden Trout. Golden trout deserve their own section, as they can be some of the most discerning and stubborn trout known to man. This is possibly because at the high elevations they thrive at, the most abundant food is often plankton, which can be tricky to imitate with flies. If you encounter this, consider using either bright, sparkly scuds or Blob Flies.

Beyond that, you just need to be persistent and versatile, and try everything.

The best regions for golden trout are Wyoming’s Wind River Range and California’s Sierra Nevada, but Montana, Idaho, Utah, Washington, and Colorado also have Oncorhynchus aguabonita.

Alpine trout are not always dumb and easy. They definitely can be, but they can also be ephemeral, indifferent, misleading, hiding snobs. Understanding when, where, and how to find these fish can set you up for success.

Specialized Gear

Packing for fly-fishing outings to mountain lakes, or any backcountry fishery, can be a confounding task. You want to pack everything you need, but you also want to keep your weight as low as possible. This is especially important when you are miles from the safety and storage of your vehicle.

Familiarizing yourself with the specialized gear for mountain lakes fly fishing can help simplify this task and give you added confidence in the mountains.

One theme to keep in mind for packing for mountain lakes: Reduce redundancy.

Rods and Reels. On my most recent trip along the Continental Divide Trail on the Idaho/Montana border, I packed a couple of Pescador on the Fly travel rods. One was a 3/4-weight 6-piece rod that only weighs 3.5 ounces, and the other was a 1-weight El Jefe - Wild Combo that weighs a total of 6 ounces—with the reel and line. It was a hoot for the “stunted-brook-trout” ponds and small mountain streams. That said, it’s a bit small for much of the fishing you’ll do even at mountain lakes so probably cannot be your only rig.

For your main rod, find something that’s relatively lightweight and that you enjoy casting. I use either an old-school Winston “Original Graphite” (O.G.) 3-weight or my Sage Circa 5-weight.

I also often pack a switch rod, with an appropriately heavy fly line. These powerful rods roll cast easier than single-handed rods, which is required at tree-lined lakes where there is no room for a backcast. I use a 5-weight Sage Z-Axis, which actually fishes more like a 7-weight single-hander, so even a 3- or 4-weight trout Spey rod would be adequate. Especially on larger lakes and those below the treeline, a switch rod improves your odds with minimal size and weight. What they lack in subtle presentation, they make up for with launching line.

Most lightweight reels will suffice. A few years ago I purchased a few plastic Orvis Encounter reels that don’t reflect light into the water and only weigh 5.2 ounces, including line and backing.

Consider heading to the hardware store to purchase a fluorescent light bulb tube guard to use as a rod case. They are cheap, lightweight, and protect your rods while hiking through trees. Alternatively, both Scientific Anglers and Trxstle make braided-polyester rod “gloves” that are expandable and flexible, and light. Or you could make your own rod glove from materials available at the hardware store.

Fly Lines. There are many different specialized fly lines for stillwaters: floating lines, sinking lines, hover (or midge-tip) lines, dual-density lines, emerger-tip lines, parabolic (or sweep) lines, and booby-tip extensions. They come in clear and colored varieties, and different sink rates.

But with regard to carrying only what fits in my pack, I usually only carry one floating line and two different sinking line options.

I carry just an all-purpose standard floating line that maintains buoyancy, is durable, visible—nothing special. Scientific Anglers (SA) even offers a glow-in-the-dark tip section for low-light situations.

I like to have a couple different sinking lines, one with a uniform sink rate and either a dual-density sinking line, which has two different sink densities in the belly section, or a parabolic line.

For my sinking lines, I prefer lines with sink rates from 1.25 inches per second (ips) to 3 ips. Bear in mind that the Type 1, Type 2, etc., sink-rate system is not standardized–it’s different for each manufacturer.

SA has a line called Sonar Stillwater Seamless Density which is dual density. I use the one with 1.25 ips sink rate and a second short belly section with a 3 ips sink rate. They also make these in heavier densities for deeper lakes where you want to get deep very quickly.

RIO Products has a robust series of fly lines, including different versions of its Midge Tip lines and a specialized floating line that casts long leaders well.

Airflo offers a wide variety of stillwater-specific fly lines that are PVC-free. Their sinking lines especially have an excellent reputation.

Then there are what’s known as “parabolic” or “sweep” lines that sink in a “U” shape as they’re retrieved. This pulls the head of the fly directly downward so as to appear like it’s diving, which some stillwater bugs do. This also just gives the fish a different look and can trigger curiosity strikes when the going gets tough.

You could also consider packing a hover line, which is a sinking fly line that drops very slowly, meant for fishing shallows or emergers.

There are also “booby tips,” which are small sections of floating lines with welded loops that you attach to the end of a sinking line, to keep your flies suspended just off the bottom.

Included in modern stillwater/sinking fly lines are what are called “hang markers.” Hang markers are short sections of tube that you heat-shrink around your fly line at either the 10- or 20-foot mark (from the tip). When retrieving your fly, the marker will “tick” the rod’s tip-top, and remind you to let the fly “hang” for a second or two. Stillwater trout will often chase your fly for long distances, so incorporating this “hang” gives the fish an opportunity to catch up and take the fly. The tick of the marker is just a little reminder.

Tippets and Leaders. Most manufacturers make stillwater-specific leaders that often have short butt sections and long tippet sections. SA, for example, makes Absolute Indicator Stillwater leaders with a bright orange or pink butt section. These are intended more for fishing subsurface but work fine for dry-fly fishing as well.

Carrying spare leaders is not necessary—just know your knots and build out the leader with tippet, as necessary. Usually, alpine anglers can get by using only 4X and 5X tippet, rather than carrying the entire spool caddy.

Packs. Select a pack based upon the length of your trip, and whether or not you’re going overnight. Overnight backpacks need to be quite a bit larger to account for the tent, sleeping pad, and sleeping bag. I am unaware of a fly-fishing-specific backpacking pack.

For day trips, I like Simms Flyweight Vest Pack. It’s lightweight and a has perfect bear-spray pocket on the front shoulder strap. It’s not huge, but if you can successfully reduce redundancy, it doesn’t need to be.

I also recently used Pescador on the Fly’s Versa Pack hip pack. It fits on any backpack or hip pack belt and is perfect for your reel, spare spools, tippet, and some flies with its built-in fly foam.

Clothing. Clothing is another easy area to reduce redundancy. For example, Simms Bugstopper SolarFlex Hoody provides both sun and bug protection. Simms Flyweight Shell Jacket is primarily a rain jacket, but also offers warmth, wind protection, extra pockets, and packs down very small. Simms Superlight Zip-off Pants can be both long pants and shorts.

Orvis’s new PRO Approach Hikers are hiking boots that double as wading boots and don’t require use of a wading sock. Remember to always give boots a test hike before embarking on a big trip. Just because they fit comfortably at first does not always mean they won’t cause blisters.

And while waders are occasionally helpful, they’re often not worth the weight. If you insist, Patagonia offers the Swiftcurrent Packable Waders, Orvis makes the Ultralight Convertible Wader, Redington has its Escape Wading Pants and Crosswater Waders, and Simms has its G3 Guide Wading Pant, Freestone Wading Pants, and are in development on other packable waders.

Inflatables. Float tubes, pack rafts, and other lightweight inflatables can be options as well. Some of them pack down to about the size of a water bottle, weigh only a few pounds, and can provide the advantage of mobility on medium and large mountain lakes.

The Klymit Litewater Dinghy, for example, weighs less than 3 pounds (not including kayak-style paddle), can double as a sleeping pad, and packs down very small. It’s a little awkward to fish out of, but will get you out there.

Float tubes can be nice, but not so nice that standard ones are worth hiking miles with, in my opinion. There are some ultralight options, however, like the Wilderness Lite Backpacker Pro float tube at only 3.6 pounds.

The lightest pack raft I’ve found is the Alpaca Packraft Ghost Scout, which is only 1.5 pounds, not including paddle.

In lieu of an inflatable, however, I often opt for a switch rod, which can roll cast long distances (see the Rods and Reels section).

Extras. Below is a list of extras I often pack, always aiming to reduce redundancy and go as light as possible. Some of these are not entirely necessary, but should be considered.

As with all fishing, a good pair of polarized sunglasses is important. I often pack a bit of whiskey (but always transfer it to a small plastic flask). For energy, protein bars or gels pack small with a big punch. I use backpacks that have slots for small water bladders, and also bring a filter so I don’t need to hike with water (which weighs about 8 pounds per gallon). Electrolyte tabs are small and also help with hydration. Definitely bring bear spray if you’re in bear country. A compact point-and-shoot camera works fine if you’re not overly concerned with print quality, and modern smartphones take remarkably nice photos. If you want better quality photos, consider either a mirrorless interchangeable-lens camera (MILC), a high-end point and shoot, or a compact DSLR. Satellite communicators such as a Garmin InReach or the new iPhone 14 (which offers the “Emergency SOS via Satellite” text-messaging feature) offer peace of mind and could save your life, as can a small hand-crank weather-band radio.

One more thing to think about before embarking: If you’re hiking in a place where forest fires are possible, learn the protocol for what to do if you end up in an evacuation area. We were confronted with this lack of preparation on our trip on the CDT last September when the smoke dramatically thickened after a thunderstorm.

We were forced to consider how we would be alerted by the USFS if a fire did come roaring up. Would they drop a chopper near us? Use esoteric hand signals we don’t know? Were they trying to find us right now, but without knowing what signals to look for, we weren’t seeing them?

The answer is that you should look for increasing low-flying aircraft traffic overhead, which could indicate there’s a fire nearby. Try to get the pilot’s attention by spreading out a bright cloth like your tent, or flashing a mirror at the craft. If and when you are spotted, the USFS will let ground firefighters know of your location, and they will assist your departure in the safest way.

As with all esoteric outdoor pursuits, there is plenty of specialized gear for fly fishing at mountain lakes. Knowing what’s available can help make your trip as comfortable and successful as possible.

Food Sources

Mountain lakes exist in a different environment than our broad, boisterous main stems. The shorter growing seasons, lack of oxygenated water, and colder water temps create habitat for a different forage base for the brook, cutthroat, golden, and rainbow trout and Arctic grayling. It pays to understand these differences.

Aquatic Insects. Many of the same well-known aquatic insects from the rivers below also exist at mountain lakes, but often in different densities and distribution. And some food sources are unique to alpine stillwaters.

For example, midges—often called chironomids at lakes—are probably the single most important food source in mountain lakes. I’ve heard it said that if there is open water, there will be midges. These bugs are often a size 16 to 20 in mountain lakes, and come in a wide variety of colors. Anglers should come prepared to imitate pupae, larvae, and adults.

The most important mayflies at alpine ponds are Callibaetis. These are speckle-winged gray or tan mayflies, usually size 14 or 16. Also keep your eyes peeled for Blue-winged Olives, Gray Drakes, Tricos, and others (though these are not very common at high elevations).

Caddis are not always important at high-elevation fisheries, but they can be. At Heart Lake in Yellowstone, for example, which sits at about 8,000 feet above sea level, we found zillions of black micro caddis, and a large, size 12 or so gray speckle-wing caddis that often wouldn’t survive more than 10-15 seconds after hatching because a trout would come slurp it up. At certain times and places, caddis matter.

Stoneflies don’t generally live in stillwaters as they require highly oxygenated water to survive, but are at times found at mountain tarns. That said, they most likely hatched from nearby high-gradient inlets or outlets and fluttered to the stillwater—but trout will still eat them. And speaking of Heart Lake, a friend of mine actually reported catching a lake trout on a salmonfly dry there recently—quite a feat. Apparently it is possible.

Dragonflies, damselflies, and craneflies are more common at fisheries well below treeline, but are periodically found at mountain lakes.

Crustaceans. Scuds, sowbugs, crayfish, and daphnia are the primary crustaceans found in mountain lakes.

Of these, scuds are far and away the most important for fly anglers; in fact scuds are the single most important food source at certain alpine lakes. They come in a wide variety of colors and sizes, including yellow, orange, pink, olive, brown, tan; usually sizes 12 to 18.

Crayfish, sowbugs, and Mysis shrimp are uncommon, but occasionally live in certain mountain lakes. Of these, I’ve had the best luck with crayfish patterns. If you’re traveling light, I wouldn’t bring imitations.

If there are visible algae and the trout are being picky, consider imitating the clouds of tiny organisms known as plankton. Plankton are minute crustaceans (daphnia or “water fleas,” copepods, baby scuds, etc.), diatoms, rotifers, protozoans, and the eggs and larvae of larger insects that feed on algae. Plankton cannot propel themselves—their movements are based on the currents and wind. They appear like globs of goo.

Some of the best plankton imitations for fly anglers are Blob Flies—simple colorful patterns often made up of flashy chenille, Fritz, Flashabou, beads, and/or marabou tied sparsely enough to appear translucent. Popular colors are red, orange, and green, and usually tied in size 10 or 12.

In fact, one theory for why golden trout can be difficult to fool is that at their high elevations, plankton can be a major food source. If you find stubborn goldens, maybe break out a Blob Fly on a sinking line.

For more information on plankton in mountain lakes, check out both Gary LaFontaine’s book Fly Fishing the Mountain Lakes and Rod Cordes’s and Randall Kaufmann’s Lake Fishing with a Fly.

I’ll also briefly mention Fairy Shrimp here. Fairy Shrimp are a very rare, federally protected endangered crustacean that typically live in seasonal oxbows, called vernal pools. Therefore if you find Fairy Shrimp, you will not find trout in this water, as these ponds dry up every year.

Terrestrial Insects. This is one case in which the bugs are basically identical to the ones that you know from fishing rivers. But there are some key differences in how high-mountain terrestrials end up on the water.

Understanding the nature of winds in the high country is beneficial for fishing terrestrials in mountain lakes. So-called “anabatic” winds blow up mountainsides, caused by differences in air temperatures. These winds can capture terrestrial insects like grasshoppers, ants, and beetles from below, and deliver them to the surface of the lake. Likewise there are “katabatic” winds, which flow down the mountainsides from above the lakes.

Quick tip: If the trout happen to be picky on terrestrials, don’t be afraid to sink your terrestrial dries.

Baitfish. Sculpins are rare at high elevations, but not entirely absent, especially at the lakes below treeline. If you see any sculpins, it’s fair to expect sizable trout as they get big eating these large meals, when and where they can coexist. That’s not to say that streamers are ineffective at lakes without sculpins, but your streamers should imitate small trout or leeches, especially when fishing lakes with natural reproduction where there will be a new class of fry and fingerlings every year. Or shortly after trout have been stocked, at stocked lakes (in Montana, for example, FWP typically stocks two-inchers). It can pay to pay attention to stocking schedules.

Other Food Sources. Of the food sources that don’t fit into any category above, leeches are the most important. Leeches are blood-sucking annelids that have a distinct wave-like swimming pattern and can be very abundant in mountain lakes. Definitely carry some leeches in your mountain-lake fly box.

You might also encounter water boatmen or mollusks like snails, but if space is of the essence, don’t worry too much about imitating them.

So, turn over rocks and keep your eyes peeled. It’s a different world up there, and it’s beneficial to understand highland bugs, crustaceans, and other trout forage.

Fishing the highlands need not be overwhelming. A little prep and knowledge can set you up for some amazing scenery, beautiful trout, and lifelong memories.

Flies

Since packing light is generally the way to go when fishing mountain lakes, you’ll want to be selective in the flies that you bring.

In my opinion, the single most important fly at alpine lakes is the Woolly Bugger. Buggers imitate a wide variety of foods including leeches, crayfish, baitfish, stonefly nymphs, and more.

Other attractor flies (that suggest a wide variety of foods rather than imitating one specifically) are great options at mountain lakes, since they can help keep your boxes minimal.

Below is a list of some of my favorites. Be sure to come prepared to imitate pupae, larvae, nymphs, and adults.

Callibaetis: Sparkle Dun, Pheasant Tails, Greg’s Emerger, RS2, Hare's Ears

Midges: Ice Cream Cone, Buzzer, Jujubee Midge, Zebra Midge, Disco Midge, Rojo Midge, Chromie, Brassies

Caddis: Stimulator, X-Caddis, Sparkle Pupa

Damselflies: Mayer’s Mini Leech Damsel, Barr’s Damsel Fly, Marabou Damsel Nymph

Terrestrials: Amy’s Ant, Fat Angie, Bloom’s Parachute Flying Ant, Chernobyl Ant, Paramore’s Thunder Thighs, Morrish Hopper; Beetles like Rene Harrop’s beetle patterns and Cathy Beck’s Super Beetle—you don’t need to get too crazy or creative.

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Joshua Bergan is Fly Fisherman magazine’s digital editor, the former associate publisher at Wilderness Adventures Press, a freelance writer and photographer, and author of the Flyfisher’s Guide to Southwest Montana’s Mountain Lakes and Tributary: Fishing the Northern Rockies’ Periphery. He, his wife Liz, kiddo Thomas, and their dogs Mika and Koda basecamp out of Belgrade, Montana.