Skip to main content

The Yosemite Boogeyman

Rainbows fear the giant brown trout lurking in California's most popular national park.

The Yosemite Boogeyman

Most people visit Yosemite National Park to see iconic landmarks like El Capitan, location of the Academy Award-winning documentary Free Solo. But the park is also home to two wild rivers with some of  California’s best trout fishing for native rainbows and predatory browns. (Jason Shields photo)

Through the tinkerings of man, the vast majority of California’s rivers have become a highly altered ecosystems. Since the era of the California gold rush in the mid-1800s, almost every one of California’s major rivers has been dammed, diverted, leveed, or otherwise altered in some way. Once a river is dammed, its natural dynamics are completely and permanently changed. Yet there are a few drainages that are still pristine in their headwaters. I call these watersheds the “Last California.” These are the rivers above the dams, the rivers that were never dredged for gold, and still flow out of intact old-growth forests or healthy High Sierra meadows. They haven’t been overrun by nonnative vegetation or choked out by poor water quality and the resulting unnatural algae blooms. In these places, snowmelt and spring water run freely over the landscape and still rise and fall with the seasons California’s Yosemite National Park is home to two such rivers, the Upper Tuolumne and the Upper Merced. However, no matter how pristine these upper rivers may still be, one shiny golden nonnative relic from the Gold Rush era remains. Most people call them brown trout or Salmo trutta. I think of them as boogeymen.

Euro Immigrants

Brown trout are immigrants to California. Their ancestors were brought here by the early European explorers as a food source and as sport for anglers. They are highly adaptable animals, and thanks to their immense allure for anglers, they have now set up shop in coldwater ecosystems in all corners of the globe. Some have even adapted to running into the ocean and returning to rivers like steelhead or salmon. In California they exhibit similar behaviors in lakes and reservoirs.

fly fishing merced river brown trout
Brown trout aren't native to the headwaters of the Tuolumne and Merced rivers, but they are all wild, and they occupy a special niche in the ecosystem. Trout haven't been stocked in Yosemite rivers since 1991. (Jason Shields photo)

You could argue that brown trout are the most prolific and successful invasive species on this planet, due to the sheer numbers of places they have been transplanted on every continent. As far as invasive coldwater fish go, they are second only to rainbow trout which are the export product of California. We sent McCloud River and Eagle Lake rainbow trout around the world, and in return we got Loch Leven and German brown trout. One thing is for sure, they are here to stay.

Because they are not native to the Yosemite ecosystem, the Park Service views brown trout as pests. For me, they are the best part of the park. As the outreach coordinator for California Trout, it’s sometimes tough for me to admit that Salmo trutta are a favorite, but they are challenging and I love their distinct colors and exotic markings. No other fish I know of displays such a variance in coloration and patterns within one species.

I am a big believer in native trout but I’m also a realist, and in some cases, there is no going back. Brown trout have been part of California’s ecosystem for over 150 years, and they have become an important gamefish. They contribute greatly to our economy and motivate more people to become involved in conservation through organizations like CalTrout.

At CalTrout we advocate for both California’s anglers and for native trout, salmon, and steelhead. These missions are sometimes in juxtaposition. CalTrout’s Sierra Headwaters initiative protects the remaining populations of wild, native trout and expands those populations back into historic ranges where possible. That effort sometimes calls for culling invasive trout like brook and brown trout and even rainbows in places where they were not historically present, and where they compete for habitat or hybridize with native cutthroat trout.

Another one of our initiatives is to protect and enhance California’s historic blue ribbon waters like the McCloud and Truckee. In the case of Yosemite, some agencies and individuals have suggested trying to eradicate nonnative trout from the park. This would be a losing battle. The Tuolumne and the Merced are both large river systems connected to large reservoirs on the lower ends, and dozens of high country lakes in the headwaters. It would be impossible to fully eradicate brown trout.

They coexist with native rainbow trout, and in many ways have adapted to occupy a different niche in the ecosystem. Coastal rainbow trout are the only one of California’s 32 distinct native salmonid species with naturally expanding populations, and they are in zero danger of becoming endangered or extinct anytime soon. If those populations inside the park ever do become stressed, it would most likely not be due to competition with brown trout. Changing climate, massive wild fires, and extended droughts are by far the greatest threats to native trout.

The Boogeyman

If you can’t beat them, you might as well catch them! If you want to catch a bunch of trout in the Yosemite area, you should target rainbows, or trek into the small streams at higher elevations, where you’ll find hordes of brook trout.

Rainbows are by far much more prolific than brown trout in both the Merced and Tuolumne. Based on my visual and angling observations, I’d say rainbows outnumber browns by about 10 to 1. The rainbows range in size from 8 to 20 inches, but that’s just a starting point for Yosemite brown trout that can run up to 30 inches.

Large browns are the alpha predator fish in these waters. If there is a 25-inch brown in a pool, any other fish 12 inches in length lives a life of fear. Large brown trout feed differently than small rainbows. Once they reach a certain size their diet switches from predominantly eating bugs to targeting larger food sources like other fish (including rainbows), crayfish, and terrestrials like mice, birds, and even snakes, lizards, and salamanders. For this reason they are much more spread out in the river system and typically require larger pools with depth and structure where they can hide and wait for their next meal to come to them. These big, bad browns feed primarily at night, and they are a small rainbow’s worst nightmare. That’s why I call these predatory big brown trout “boogeymen.”

If you want to catch the boogeyman, you’ll need to adapt your techniques and also change your attitude. Prepare to suffer through disappointment. If your plan is to target large brown trout, you’ll often leave the water skunked. But if you can dedicate yourself to catching one trout every once in a while, hunting the boogeyman might be the game for you.


Upper Tuolumne River

The upper Tuolumne River is widely considered to have the best fishing in the park, but you’ll need to hike a minimum of 7 miles to get into the big fish. Very few people fish this remote stretch of river. There are lots of feisty wild rainbows and the fish are eager to eat a fly. Fishing in the park is open for standard trout season in California, but you should plan your trip well after the spring run-off as the river is often too high and dangerous to fish around the season opener. Highway 120 and all the trails close in the fall after the first snows.

The upper Tuolumne starts as snowmelt from the peaks near Tioga Pass. There’s several places you can park along the highway and easily access the river with a short walk from the road. The Tuolumne is shallow and meandering through the big sweeping meadow. There are some nice undercuts and some fallen trees and other structure that hold fish. It’s mostly smaller fish, but plenty of fun with a 4-weight and a dry fly. The water is low and clear in the summer months, and stealth is a must when fishing in these higher elevations.

From Tuolumne Meadows, the river quickly drops into a deep gorge nicknamed the Grand Canyon of the Tuolumne, and eventually into the Hetch Hetchy Reservoir near the west boundary of the park. There’s a trail that follows 20+ miles of the river until it breaks off at Pate Valley and heads back up to Camp White Wolf. The last 3 or 4 miles of cascading river descend through a wilderness on faint game trails until the flows soften into the flat waters of Hetch Hetchy Reservoir.

Altogether it’s a 32-mile loop if you make the full pull from Tuolumne Meadows to White Wolf, and you will need a wilderness permit to camp overnight along the trail. Plan on at least four days and three nights to complete the entire loop if you plan to stop and fish all the amazingly clear, deep pools along the river.

Trout were not originally native to the upper sections of the Tuolumne River, but for more than 100 years, rainbows, browns, brookies, and even golden trout were stocked throughout Yosemite. The National Park Service stopped planting fish in the Tuolumne in 1991, so all the trout are now wild, self-sustaining populations. There’s a series of larger waterfalls along the upper Tuolumne near the top end of the Grand Canyon, including the iconic Waterwheel Falls near Glen Aulin Camp. In high water, wind gusts carry the enormous water spray back up to the top of the falls, a cyclic “waterwheel” that gives the falls an appropriate name. Later in the summer, the smooth granite plunge pools form natural water slides for swimmers.

fly fishing merced river
The Merced in Yosemite Valley is wide and slow. Fishing typically requires long casts and a stealthy approach. Downstream of Highway 140, the river cascades through a boulder-strewn canyon with pocketwater and a few deep pools. (Jason Shields photo)

In this area, the fish are somewhat isolated and tend to be smaller. Farther down near the Pate Valley, the gradient eases off and there’s good connectivity between pools and runs where larger fish can hunt and wander. If you plan on targeting trophy trout, focus your efforts on the lower sections of river. The quickest way to this section is to hike in from White Wolf Camp. It’s 8 miles to the river from there, and a 4,500-foot elevation drop. It’s a leg burner walking out, but the scenery is spectacular and you’re into prime water as soon as you reach the river. There are lots of great campsites that allow you to make day trips up and down the river and leave your heavy overnight pack behind.

The water in the lower canyon is a series of runs, riffles, and some deep pools. In the summer, the majority of the fish are in the runs and riffles, where a standard hopper/dropper rig on a 9-foot, 5-weight rod works just fine. The fish don’t see a ton of pressure so basic dry-fly attractor patterns like Stimulators, hoppers, flying ants, and Humpys work well. For nymphs, try a Poxyback Golden Stone, Beadhead Pheasant Tail, or Mercer’s Micro May. Most trout here are 8- to 15-inch rainbow trout, but the boogeyman may be lurking in nearby depths and shadows.

The last time I fished the canyon, a friend hooked a 10-inch rainbow on a dry fly and was bringing it across the pool when an enormous brown snatched the rainbow sideways in its jaws, like a junkyard dog gnawing a bone. The rod bent over and after a few violent head shakes, the rainbow popped out of the brown’s mouth. The brown hovered around and made a couple more swipes at the trout as it darted toward the safety of the shallows. It just about jumped into our hands to get away. I quickly tied on a big streamer, but couldn’t get the big brown to come back. We had to hike out that afternoon, but if I had more time, I would have given that big fish another try in the evening.

If you plan on targeting the larger browns in these deep pools, you will need to bring a stout 5- or 6-weight rod and use a sinking-tip line with some big, heavy streamers. The boogeyman needs a victim. I tie heavy sculpin and redside minnow patterns on jig-style hooks with lead eyes for these waters. During the summer, the best fishing for large trout is in early morning or late evening. Plan your strategy so you can camp at one of the best-looking pools to take advantage of these prime fishing hours.

If you’re feeling adventurous enough to chase the park’s biggest trout, you can hike down the Tuolumne to where it flows into Hetch Hetchy Reservoir. Once you cut off from the main trail at Pate Valley, you have to bushwhack downriver using a series of bear trails and boulder hopping. It’s not for the faint of heart and only recommended for experienced hikers. About 3 miles down from the main trail (a mile above the lake) there’s a steep cascade in the river and a huge boulder garden—the result of an ancient rock slide. The boulders range from the size of cars to the size of houses.

I’ve only made it all the way to the back of the lake once. We made the trek in the late fall. The fishing was good for big browns in the river and also in the reservoir itself. On more than a few occasions, we cast a streamer out into the clear water of the lake and two to three fish would rush at it from different directions and fight to eat it first. It made for some incredible visuals in the clear water.

The Merced River

A much more accessible option for big trout in Yosemite is the Merced River. The Merced flows through the heart of the iconic Yosemite Valley before descending a steep boulder-filled canyon leading down Highway 140 to the west boundary of the park near the town of El Portal. From there it winds its way down to McClure Reservoir.

The headwaters of the Merced River create some of the most iconic and most photographed waterfalls in the world including Upper and Lower Yosemite Falls, Bridal Veil Falls, Nevada Falls, and Vernal Falls. The tributaries that form the main river flow are unobstructed wilderness rivers that run cold, clear, and clean and with a completely natural flow. That means the river is extremely high during the spring runoff, and low and clear by the end of summer.

Because the upper river and tributaries flow completely through the wilderness of the park, they have some of the cleanest water and least-disturbed aquatic habitat in the state. The valley hasn’t been commercially logged in over a century, and it was never dredged for gold, so it still has old-growth trees.

fly fishing merced river
As the Merced cuts and winds through Yosemite Valley, it eats the sand and rocks away from the roots of trees. Deep holes along these rootwads provide some of the best aquatic habitat for trout. Brown trout markings are perfect camouflage for the shadows and dark colors of submerged woods, and they're also favored hiding spots for baitfish and aquatic insects. (Jason Shields photo)

Because there is little development along the river, no engineering has been done to the riverbanks to protect human infrastructure and thus the river is left to naturally migrate through the soft sediments of the valley floor. As it cuts its way through new channels, it eats the sand and rocks away from roots of trees. Many of those trees fall into the river. Big wood provides some of the best aquatic habitat for a multitude of species, including trout.

Mother Merced and the Yosemite Valley see tens of thousands of visitors a year, but very few of those people come specifically to fish. There is no trout stocking in the park, so it’s completely a wild trout fishery with catch-and-release regulations on all rainbows. Due to the nature of the pristine habitat there is a fairly good distribution of wild trout. Every spot that looks like it should be holding a fish, usually is. The fishing is good at times, but it’s not easy. To target larger fish, focus your efforts on the main river from roughly Half Dome Village to the park entrance along Highway 140. If you get up into the tributaries, you will find only smaller wild rainbows.

Yosemite Valley sits at just under 4,000 feet elevation, so you really feel the seasons there. Spring, summer, fall and winter are distinctly different in the valley, and fly fishers need to adapt to the seasons. The river can be very dangerous to fish in the spring and early summer when runoff is high. Use extreme caution in these conditions. The Merced claims lives every year. The flows are deceivingly strong, the water is cold, there are lots of strainers in the river, and if you take a swim in waders it can be difficult to get back to shore.

Summer produces heavy crowds of tourists, lower flows, and warming water temperatures. In the hot summer months, focus your fishing in the morning and evening when the sun is off the water and temps are cooler. In the fall, the flows get very low and clear and fish can be spooky. The river is closed during the winter, so no need to worry about tromping through the snow with waders on.

When I think of fishing the Merced in Yosemite I kind of think of it as two distinctly different sections. You have the slow meandering waters of Yosemite Valley, but directly below where you cross the river as you enter the lower end of the valley on highway 140, the character of the river completely changes as it drops into a tight boulder-filled canyon characterized by pocketwater and a few deep pools.

The valley water is open and slow. Fishing there typically requires longer casts and a stealthy approach. There’s lots of long runs with perfect current for drifting dry flies. Don’t be afraid to try big attractor patterns like hoppers, beetles, and flying ants, and don’t be surprised if you end up matching mayfly or caddis hatches. I’ve seen awesome hatches of Baetis and Ephemerella mayflies, Brown Drakes, and lots of midges. During midge hatches I most often tie on a size 14 Quigley Hackle Stacker mayfly in gray or pink, or a good old #18 Parachute Adams.

When targeting larger trout, streamers are undoubtedly the most effective. Look for big-fish habitat, and focus your attention in those areas. Large fish will not be just sitting out in plain view or cruising the shallows where you can easily see them. Big browns like places where they can hide under something and ambush their prey from the shadows. That doesn’t necessarily mean they will always be in deep water. Look for areas where there’s a big boulder in the river that breaks up the current.

fly fishing merced river brown trout
Yosemite recieves an enormous amount of snow, and its rivers run high and fast until early summer. Plan your fishing to coincide with lower flows in mid-summer or early fall. (Jason Shields photo)

Browns in this river also gravitate toward submerged trees. Big wood breaks up the current, creates deep scour spots, and provides places for big trout to tuck up and hide. Luckily there are a ton of fallen trees in the river through the Valley. Brown trout markings are perfect camouflage for the shadows and dark colors of a submerged tree. Big wood also provides lots of habitat for bugs and great cover for baitfish.

The Merced has sculpin, redside minnows, and lots of California suckers, which are a favorite food for big browns. Crayfish also tend to favor that woody habitat, and browns will key in on them, especially in late summer when they molt and become soft.

Undercut banks are also great hiding spots for large trout, and the naturally winding river in Yosemite Valley has lots of them. If you’re approaching the river from the steep side, make sure to drop your fly along any undercuts before approaching the water and potentially spooking trout that could be sitting right under the bank.

The valley is also home to lots of rodents, including a huge population of field mice. The tall grass and steep dirt drop-offs lead right up to the banks of the river in many places, and you can bet lots of mice, voles, and gophers meet their fate in the Merced. Don’t overlook a mouse pattern in the right situation.

For streamer fishing in the valley, try a stout 6-weight single-hand rod or a 4-weight switch rod. Switch rods can be great for some of the areas where there are lots of trees around the river, and fewer areas to backcast. In situations where there’s current, even slow current, I use a heavy sinking-tip line. A short but heavy head helps your fly get down, but you will still be able to mend your floating running line to control the speed of the fly.

When targeting big browns, retrieve the fly in short jerky stripping motions, then let it swing naturally across the current like you would for a steelhead. These large predatory trout are aggressive and can cover a lot of water very quickly, so it’s more important to get their attention and force them make a decision quickly. Almost all their food sources swim, and some swim very quickly. Try to imitate an injured baitfish, which would twitch, twitch, twitch then stop, twitch, twitch, twitch then stop.

If nymphing is your thing, you might want to try the bouldery pocketwater along Hwy 140 in the west end of the valley. There’s lots of places you can pull off the highway and easily access some great pocketwater. The water is swift in this area and the rocks can be slick so be careful when wading. I don’t recommend spiked wading boots, as carbide points will not provide good traction on the slick, hard granite. Aluminum surfaces stick best to the granite here. Be careful of foot traps, and use a wading staff at all times.

Because the water is more swift and the boulders are bigger at the west end of the valley, you can typically get much closer to where the fish are holding, which makes tight-line nymphing a great option. Standard indicator nymphing also works well, but don’t be afraid to add split-shot, take off the indicator, and let your nymphs drift deeper into some of the big, darker holes. Watch the tip of your floating line for strikes. Try Poxyback Golden Stones, Squirrel Tails, big Hare’s-ear Nymphs, Beadhead Pheasant Tails, Micro Mays, and Baetis patterns for droppers.

Mikey Wier grew up in the Sierra foothills where he split his time between snowboarding and fly fishing. He spent 15 seasons fishing and guiding the waters of the Truckee, Carson, and Walker rivers. He also started BURL Productions, producing outdoor films like Trout Bum Diaries 1, Soulfish, and Cali Rush. He is a Patagonia ambassador and outreach coordinator for California Trout. 

GET THE NEWSLETTER Join the List and Never Miss a Thing.

Recommended Articles

Recent Videos

The Fly Fusion Trout Tour is a perfect excuse to get together with friends while watching an epic collection of trouty f...

The Tightest Line

The Fly Fusion Trout Tour is a perfect excuse to get together with friends while watching an epic collection of trouty f...

How to Tie Craven's Mr. Jones Dry Fly

The Fly Fusion Trout Tour is a perfect excuse to get together with friends while watching an epic collection of trouty f...

How to Tie Craven's Mr. Jones Dry Fly

The Fly Fusion Trout Tour is a perfect excuse to get together with friends while watching an epic collection of trouty f...

How to Fight Trout Effectively and Get them in the Net Quickly

The Fly Fusion Trout Tour is a perfect excuse to get together with friends while watching an epic collection of trouty f...

Patagonia Advocates for Dam Removal

The Fly Fusion Trout Tour is a perfect excuse to get together with friends while watching an epic collection of trouty f...

Science in the Thorofare

The Fly Fusion Trout Tour is a perfect excuse to get together with friends while watching an epic collection of trouty f...

How to Tie the Picky Eater Perdigon

The Fly Fusion Trout Tour is a perfect excuse to get together with friends while watching an epic collection of trouty f...

Fly Fishing the Plunge Pools of Yosemite Falls

The Fly Fusion Trout Tour is a perfect excuse to get together with friends while watching an epic collection of trouty f...

Scientific Anglers Launches Reimagined Tropical Saltwater Fly Lines

The Fly Fusion Trout Tour is a perfect excuse to get together with friends while watching an epic collection of trouty f...

Check Out Grundens' New Vector Wader!

The Fly Fusion Trout Tour is a perfect excuse to get together with friends while watching an epic collection of trouty f...

Fly Fishing the Plunge Pools of Yosemite Falls (trailer)

The Fly Fusion Trout Tour is a perfect excuse to get together with friends while watching an epic collection of trouty f...

Fly Fusion Trout Tour Sizzle Reel

Fly Fisherman Magazine Covers Print and Tablet Versions

GET THE MAGAZINE Subscribe & Save

Digital Now Included!


Give a Gift   |   Subscriber Services


Buy Digital Single Issues

Magazine App Logo

Don't miss an issue.
Buy single digital issue for your phone or tablet.

Buy Single Digital Issue on the Fly Fisherman App

Other Magazines

See All Other Magazines

Special Interest Magazines

See All Special Interest Magazines

GET THE NEWSLETTER Join the List and Never Miss a Thing.

Get the top Fly Fisherman stories delivered right to your inbox.

Phone Icon

Get Digital Access.

All Fly Fisherman subscribers now have digital access to their magazine content. This means you have the option to read your magazine on most popular phones and tablets.

To get started, click the link below to visit and learn how to access your digital magazine.

Get Digital Access

Not a Subscriber?
Subscribe Now

Enjoying What You're Reading?

Get a Full Year
of Guns & Ammo
& Digital Access.

Offer only for new subscribers.

Subscribe Now