Jurassic Trout: The Megafauna of Lago Strobel

One of the wildest stories in trout propagation began in Argentina in 1994 when estancia owner Alberto Rodriguez released rainbow trout from the Rio Santa Cruz into the Rio Barrancoso. His goal at the time was aquaculture. He wanted to farm fish. This strain of McCloud River rainbow trout had already been successfully transplanted around the world, and the Barrancoso was the largest tributary of Lago Strobel, an alkaline desert sink with no outflow, acres of weed beds, and no native salmonids of any kind. The 65-square-kilometer lake—which formed on the greater Patagonian Steppe during the last ice age—is cold and clear, and every rock and piece of vegetation in the lake crawls with scuds and midges.

Rodriguez hoped the trout would become a commodity, and that within a few years, he’d be shipping fresh fish along with beef, mutton, and wool. His plan to diversify the ranch economy worked, but not as he’d planned. The trout made their way into Lago Strobel, where they fed heavily, and grew at a staggering rate. Mature fish soon returned to the Barrancoso to spawn, and within a few years, Rodriguez’s family and friends were catching massive rainbows, and lots of them.

In 2005 Christer Sjöberg (founder of Loop Tackle) saw photos of these giant trout and organized the first group of outsiders to visit the lake. On a globe, the lake seems reasonably close to already thriving and well-known sea-run brown trout locales like the Rio Gallegos, but in reality the drive to the estancia was a massive undertaking. One of Sjöberg’s companions called the overland 13-hour ride in four-wheel-drive vehicles “the drive from hell,” but the group was rewarded with unimaginable fishing. That grueling overland marathon took them to another world, a place where they were completely isolated by the weather and the terrain, and everything was bigger—the landscape, the lake, and especially the slobberknocker collisions with rainbow trout that regularly weighed into the teens. At the time, the Jurassic Park film franchise was at its zenith, and as many fly fishers are wont, they gave their secret honey hole a fictitious name: Jurassic Lake.

The Early Years

As it turns out, the cascading Barrancoso serves as an perfect spawning and nursery environment for rainbow trout. Adult trout reproduce almost continually in the Barrancoso through the summer season of the Southern Hemisphere, providing a steady stream of juvenile trout to forage in the fertile waters of Lago Strobel. While the peak spawning activity occurs in October and November, there are spawning trout in the upper river almost continually until the ice and snow come in late April and early May. (There may well be spawning after the snow falls, but no one is there to observe it.)

As the only natal stream of any significance in the watershed, the Rio Barrancoso is vitally important for spawning, but the trout in this lake are drawn to it for many other reasons. The lake is loaded with food, it’s cold, and the wind and constant wave action keep it highly oxygenated, but for whatever reason, the trout love the scent and the current of this small stream. They often gather at the mouth, feeding on midges, beetles, scuds, and whatever else the river brings to them.

I witnessed a gathering of these trout one afternoon in January. For a few hours under darkening skies and the threat of rain, hundreds of trout (possibly many more) milled about near the shelf where the river gravel drops away into the lake. You could see the fish in the window of each wave as it rolled toward shore, and you could see them finning and rolling at the surface in the flat breaks between the waves. We caught them sometimes two and three fish at a time for several hours, constantly experimenting with what types of flies, retrieves, and depths worked best. We didn’t leave until we heard our own dinner bell ringing that night, and the next morning with sunny blue skies, most of those fish were gone—at least for a few hours.

As a pioneer, Sjöberg realized that the junction of the Rio Barrancoso and Lago Strobel was a magical spot, and after his first trip there, he made plans with the estancia owner to set up a sport-fishing camp called Loop Adventures just inside the protected elbow of the river mouth. Those early years were tough. Even though the fishing was unlike anything else on the planet, and the roads gradually improved over the years, the remaining five-hour drive from El Calafate was uniformly horrible. The accommodations were in geometric white dome tents designed to withstand the battering winds of Patagonia. Calling it “rustic” was a bit of a whitewash. It wasn’t a place for the faint of heart.

Civility came to Jurassic Lake in 2010 when a new Argentina-based company took ownership of Jurassic Lodge and began construction of a crushed rock airstrip on the plateau above the lake. They also got rid of the tent camp and built a bona fide lodge with spacious rooms (double accommodations) private bathrooms, and a dining room and great room with a view of the lake. Now that you can easily fly to the lake—just one hour from Comodoro Rivadavia, Argentina—and sleep in comfortable beds, the fishing seems more like a guilty pleasure rather than the reward for extreme hardship.

The lodge is managed by South African Llewellyn Claven, a gracious host with decades of international fishing experience in places as varied as Bolivia and the Seychelles. Evenings in the lodge’s great room with a crackling fire, Argentina Malbec, gourmet food, and Llew’s fishing stories are all part of the Jurassic Lake experience.

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Getting Schooled

Because the water is so clear in Jurassic Lake, and there are so many large trout, it’s likely the best place in the world to learn how to fish stillwaters effectively. You can see how the fish react to your flies, and good technique often pays off. This type of feedback loop is especially gratifying when it’s immediate, and the rewards are the biggest trout you’ve seen in your life. However, don’t take this to mean the fishing is easy. It’s not.

Mature trout on Lago Strobel can pack on 2 pounds of weight in a single month when they aren’t engaged in spawning or locked under ice. They gain weight like this because they have much more food than they can eat. Imagine yourself after just eating Thanksgiving Day turkey. Your stomach feels as though it is bursting, so you sit on the couch to watch football. You are so full, you would never get up and walk to the kitchen to fix yourself a snack. It’s not worth it. However, if someone strategically placed a piece of pumpkin pie just an arms-length away, perhaps you’d reach out and grab it.

It’s the same way with Jurassic Lake rainbows. They don’t feed during every hour of the day. Sometimes they simply aren’t hungry, and as a result they aren’t in their primary feeding zones along the rocky shoreline or at the river mouth. When they do appear in these spots in great numbers, they still aren’t in a mood to chase your fly or change levels to feed. They are fat and well-conditioned to accept only the easiest meals. You’ve got to get your fly where it takes little effort for them to consume it.

Your retrieve should be universally slow. No matter what fly you’ve got on, you want to move it very slowly or not at all. The trout will not chase after fast-moving prey, and if you move the fly too quickly, you’ll pull it away from a specific trout or out of a strike zone. Your goal in retrieving line is merely to stay in contact with the fly, and to keep the fly at a specific depth and in a target area like a lakeshore shelf as long as possible. Just tease the fly slowly using a hand-twist retrieve or long, super-slow strips, drawing just enough line to feel the plucking inhalation of a 16-pound rainbow.

The fly also has to be something they want. Just as pie might be the only thing to pique your interest after Thanksgiving dinner, fly selection is critically important. In Jurassic Lake, trout feed almost exclusively subsurface on scuds, midges, leeches, and to a lesser degree, small juvenile trout. Your fly boxes should have robust selections of olive, tan, and pink scuds, and black, white, olive, and rusty leeches.

I had excellent success with Ken Morrish’s Jurassic Scud with palmered hackle and a shellback made of deer hair. The important part of this fly is the #8 Owner Fly Liner hook. Regular scud patterns on regular trout hooks are inadequate, as the trout are too large and too powerful, and they will simply bend out a thin wire hook. My best trout came on a pinkish tan scud pattern tied by Dennis Pastucha. I named it the Scudmuffin. He used the same sturdy #8 hook but with all-synthetic dubbing material, Krystal Flash, copper wire for segmentation, and a UV resin shellback that adds weight and creates a wobble to the fly.

Balanced Leeches should also be part of your arsenal. Regular conehead, beadhead, and most other weighted leeches nosedive when you stop retrieving them. Balanced Leeches are designed to be fished under an indicator, and they stay horizontal in the water even with a slow retrieve or no retrieve.

If you are buying them, look for Pyramid Beach Leeches (flyshop.com) or any other type of Balanced Leeches designed for Nevada’s Pyramid Lake because they are tied on heavy hooks designed for massive fish. Pyramid Lake is the only lake in the Lower 48 where you’ll regularly run into trout big enough to mangle regular trout hooks. When you are using 1X and 2X tippet, the hook is often the weakest part of the equation, so you need flies designed for heavy tippet and large trout.

Also keep in mind that all of the fishing in Jurassic Lake is on foot by wading. Powerful winds on the Patagonian Steppe make boats impossible, and your backcast almost always sails over or through boulder fields behind you. Cheap hooks will break on these rocks and you will lose fish—maybe the biggest trout of your life.

While lake fishing from a boat can sometimes be a boring affair, stalking the shorelines of Jurassic Lake is the complete opposite. Yes, you can make long, searching casts into waves and dark water. You can also suspend your flies under an indicator and have the up-and-down movement of the waves bring your flies to life. Every cast into this lake has the potential of ending in a 20-pound+ fish.

But what is truly exciting about this lake is the sight-fishing opportunities in extremely clear water. When these fish are feeding, they naturally gravitate to the contours of the shoreline, weaving through submerged boulders or following the straighter lines of the drop-offs and shelves. These fish often ride high in the water, they are large, and they move slowly, so they are easy to see, and you often have adequate time to get into position and make the right cast. The problem is the frustrating wind. Because the trout often move slowly you can’t lead them too much, the fly has to appear within 12 inches of the fish for any consideration, and even then they can be whimsical about what they will and won’t eat.

When you can feed one of these fish and watch it happen, you’ll see that it’s rarely a smash-and-grab by the trout. They just suck in water—and your fly—and all you feel is a gentle plucking of the fly line.

One of the best places for this type of sight fishing is the Bay of Pigs, just a short walk from the lodge in a cove protected by a spectacular ridge of white rocks. From high on the rocks you can watch the trout moving slowly along the shoreline—often just three or four rod lengths from shore. The angle of the shoreline and protection from the prevailing wind make it one of the best beats for sight fishing. Another of my favorites is a cove called tat-tas. While it’s a 45-minute drive to get to tat-tas, the white alkaline rocks and clear blue water make the scene look almost tropical, and in the late afternoon, groups of large trout often work themselves around the windswept corner and into the shallower, calmer parts of the bay where you can sight-fish to them.

River Fishing

While many of the most popular beats at Jurassic Lake are at the river mouth or along the windswept shoreline, there are plenty of opportunities to fish moving water, and it’s some of the best small-stream river fishing in the world for large trout. The high-gradient river tumbles down the Steppe toward the lake quickly, but there are at least a half dozen named pools and runs, and you can find trout sheltering behind almost every boulder and in nooks and crannies along the river bottom.

All summer, the river is loaded with juvenile trout—so many small trout that they become a major hindrance in catching the big ones. You have to appreciate and enjoy all those small fish because that’s what keeps Jurassic Lake so healthy.

The best ways to avoid those small fish are to use large flies/hooks or to sight-fish and target larger fish exclusively. Mouse fishing and streamer fishing are the best ways to “fish the water” and weed out smaller trout. A slow swing with a black leech pattern or a floating mouse pattern can draw out the most aggressive fish from the pack. You can get these fish to smack a large fly any time of day, but as with most places, the hour before sunset seems to be the magic hour for mouse patterns and other large flies. When the sun sits low on the horizon, and the clear water turns to gunmetal, the trout seem to readjust their eyesight, and also their role in the ecosystem. They go from prey (herons, seagulls, and mergansers love to peck at them) to predator, and are much more willing to smash a fly that wiggles and squirms its way into their territory. One evening on the river, I landed a large trout on a rubberlegs Stimulator, and I looked upriver to watch my friend Red Kulper expertly tease a mouse pattern away from the opposite bank. The wake of a large trout followed the mouse all the way from the bank to midriver, gaining on it as the fly slowed to a crawl, and I watched the white maw of the trout completely engulf the foam-and-fur creation. I still had the net in my hands, and I scooped the trout for him. We admired its crimson flanks and compared the 31-inch specimen to a West Coast summer-run steelhead. The genetics and the behaviors are the same, but these trout have somehow evolved and adapted themselves to the Southern Hemisphere.

When the sun is high, this is the perfect river terrain to use large boulders to peer into the deep slots where you can see and target large rainbows. You’ll see both silver fish and darker fish—at times it seems as though you are looking at two different species. The darker fish have been in the river the longest, and exposure to UV light, a change in diet, and their metabolism create a river camouflage that helps them blend in against the black mossy rocks of the river bottom.

The obviously silver fish are new to the river system and are “fresh” from the lake. These fish are more aggressive, they are heavier, and they have explosive speed and acrobatic power. These are the lake-run fish you want to target when you are sight fishing.

Through anecdotal recapture, the guides have confirmed that the black fish do return to the lake, gain weight, and once again become silver. The guides say the trout spawn high in the headwaters beyond the ranch property, where the river has a gravel bottom and a weedy, spring creek character. While many of the fish you see and catch on the tumbling lower Rio Barrancoso are on their way to and from their spawning grounds, none are actually spawning.

There are also resident river trout that feed on aquatic insects, eggs from spawning trout, snails, and terrestrial insects. These aren’t juveniles with parr marks or monster lake-run fish, just “medium-sized” rainbows that for whatever reason decided to stay in the river to feed. These fish have normal fluvial rainbow coloration and tend to be slimmer and more streamlined than their lake-run cousins. They run from 16 to 24 inches, and most of them would make your day if you caught one in Montana. Here, they are mostly ignored when you are searching for true giants.

The biggest named pool on the lower Rio Barrancoso is called the Aquarium Pool or merely The Pool. It lies in an obtuse corner of the river with a high sod and glacial gravel bank on the outside of the bend, and shallow, easy wading on the inside of the bend. The high bank provides a vantage point, and protection from the wind when you’re casting from the other side. The head of The Pool flows smoothly over gravel and a few bowling ball boulders and drops into wide, deep pond with almost no current. The current only picks up at the tail, where the deep stillwater section narrows and picks up speed before plunging into a series of cascades.

The trout at the head and tail of The Pool are dependable feeders and the current forces them to make quicker decisions as food passes by. But Julian Escalada, one of the lodge’s principal operators, showed me how to use small beetle patterns in the slow water through the gut of the pool. It seems that these trout just can’t resist a size 16 or smaller foam beetle, particularly late in the day when they are looking up.

I watched Escalada cast his single dry fly over the deep slow water one evening. It was the same part of the pool where earlier that day I’d seen roughly 75 or 100 big trout hugging the bottom. Escalada cast his beetle gently over this pod of fish and waited. And waited. He didn’t fight the wind, he just patiently watched the tiny speck of indicator yarn on his fly and eventually—sometimes after two or three minutes of waiting—it disappeared with barely a ripple. Escalada set the hook, and about half the time it was a giant lake-run trout. I watched him use the same fly and tactics in the lake at the river mouth. While the rest of us were casting and casting, and casting again, Escalada was patiently waiting like a heron. He made the fish come to him. It seemed like during some evening hours, he got a fish on every cast. To giant trout like this, the fly is essentially a tiny black speck, but either they eat a lot of beetles, or else it looks close enough to a midge adult or midge cluster. Either way, they slurp it up, and it’s a fly type not many people bring to Jurassic Lake. In those glorious calm evening hours, it allows you to use delicate tackle. Escalada used a 4-weight T&T Paradigm and 3X tippet. 

Other Activities

Early mornings and late evenings are the best times for fishing at Jurassic Lake, and that leaves plenty of time at midday to feast, take a siesta, and even do a little sightseeing. The estancia is a massive parcel of land (80,000 acres) and the landscape is unlike anything you can see in the U.S. The Patagonian Steppe is technically the eighth largest desert in the world because it lies in the rain shadow of the Andes. Lago Strobel and the connecting Rio Barrancoso valley is an oasis with flowering yellow Benthamiella (a member of the nightshade family), pink Acantholippia, sticky-sweet-smelling paramela (Adesmia boronioides), and evergreen calafate. The blue/purple berries of the calafate shrub (Berberis microphylla) are an important party of Patagonian folklore—a delicacy for jams and jellies today, but likely an important reason indigenous people were able to survive in this land before the arrival of Ferdinand Magellan.

If you visit Lago Strobel, don’t miss the opportunity to visit the sheltered overhanging cliff faces where you can find petroglyphs from the early Holocene era, when the lake levels were far different. There you’ll find shavings of black obsidian from Pampa del Asador more than 300 kilometers distant, a reminder of the remarkable trade network that must have existed for these hunters to obtain knives and spearpoints they needed to hunt Darwin’s rhea (a large flightless bird), and guanaco, a camelid native to South America that is closely related to the domesticated llama. Rainbow trout and fly fishers are new to Jurassic Lake, but this is a land steeped in rich history. 

Tackle

With trout this size, and the Patagonia wind that roars down from the Andes, Jurassic Lake requires some specialized tackle you likely wouldn’t use on your home waters. I’ve already mentioned the importance of heavy-wire hooks—this is your point of contact with the trout and if you don’t have the right hook, frankly nothing else matters. You’ll use mostly 1X and 2X tippet, although when the wind dies down and the lake goes flat you might need 3X or even 4X tippet. You don’t stand a chance with anything lighter.

We used 7- and 8-weight G.Loomis NRX+ rods through most of the day while fishing the lake beats. We looked forward to the evenings when the winds calmed and allowed us to use 6-weight NRX+ rods. They proved more than up to the task for the difficult casting conditions, but more importantly, they were great fishing tools. There’s more than the wind to think about here—when you see trout they often aren’t out at the end of a 70-foot cast, they are close, so you need a rod that loads quickly to make accurate shots. You’ll need to constantly mend line to deal with the sideways currents created by wind and keep your line straight so you can feel the sometimes subtle takes. Don’t get fooled into bringing a broomstick: Jurassic Lake isn’t a distance-casting competition.

Two-handed rods with Skagit lines make it almost effortless to make days of long casting, particularly when the wind is at your back and you can unload a single overhead cast. However, they are a disadvantage in sight-fishing situations, and it’s a pain to travel internationally with oversized rods, as they force to you use an additional piece of luggage.

The lines you use are likely even more important than the rods. The best line here is easily the Scientific Anglers Amplitude Smooth Anadro line. It’s 1.5X heavier than the AFFTA standard, so it has the weight you can use to your advantage in the wind, it turns over larger flies, and it loads your rod quickly and easily for those closer shots when they unexpectedly appear. It also has a long rear taper to help you make big mends in the line. It’s important that you mend to keep your line straight so you have constant contact with your fly, and you can feel it when a trout inhales your scud.

I experimented several days with a Sonar Intermediate sinking line. The narrow diameter helped me cut through the wind effectively, but much of the time I felt that my fly was actually below feeding fish. Alternatively, it seemed that I had to retrieve the fly too quickly to keep it off the bottom. These trout are not fond of chasing their prey, and when they feed they are generally high in the water column, so a floating line works best.

Many people use a balloon-type indicator like an Air-Lock or a Thingamabobber along with a slow retrieve or no retrieve to keep their flies suspended and to register strikes, but a bobber is hard to deal with in the Patagonia wind and is unnecessary since you don’t use much weight. Instead of an indicator, just use an Amplitude Smooth Anadro line with a Stillwater Indicator tip with alternating bands of orange and optic green so you can keep track of the fly line tip.

The Rio Barrancoso is a small river, a stream actually, and the complicated currents require short, accurate casts, and casting short in a stiff wind is more difficult than many people realize because a short length of line often doesn’t load the rod adequately, and doesn’t have the kinetic energy to hit the target. A 6-weight rod with a 7-weight line, or a situation-specific line like the Scientific Anglers Amplitude Creek Trout gives you a definitive advantage in these situations. The Creek Trout line has a short, heavy head for use in small streams where you make casts like this and often find yourself roll casting.

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Ross Purnell is the editor and publisher of Fly Fisherman.