Fly Fishing in the Garden of Eden

Since that first encounter, I’ve fished the stunning and remote rivers of Untamed Angling's Tsimane fishery in Bolivia and the wide waters of Argentina’s Paraná River, and caught some spectacular specimens of this extraordinary genus. Marcelo Perez, along with another great friend, Rodrigo Salles, is one of the founding partners of the groundbreaking Untamed Angling operation. He pioneered the Tsimane operation that has become one of the most celebrated dorado fly fisheries in the world. Untamed has done remarkable work partnering with local indigenous communities across the most remote corners of Brazil and Bolivia to open extraordinarily exciting and sustainable catch-and-release fly fisheries that have captured the imagination of the fly-fishing world.

Two years ago, Marcelo told me about a new operation that he was in the process of pioneering. He talked passionately about a remote river where huge dorado from beyond an angler's wildest dreams swam unmolested in clear mountain waters. High up in the remote Yungas forests of southwest Bolivia, the Tarija River comes snaking down out of the Golden Mountains, a range of craggy peaks that mark the Eastern edge of the mighty Andes.

The “Yungas” is a magical land.

Yungas is a Quechua and Aymara word meaning warm valley. Bolivia’s altiplano makes an abrupt and spectacular stop at the Cordillera Real. On the eastern side of that wall, the land falls away for thousands of feet in a single, uninterrupted slope down towards the Amazon basin.

The Yungas is that slope.

In less than 60 miles, the landscape transitions from glaciers and the thin, cold air of the Andes, at an altitude of over 15,000 feet, to a humid jungle of banana trees, tree ferns and coffee plantations. The terrain is characterized by narrow, sheer-sided valleys and near-vertical slopes that plunge up to 7,000 feet from the high ridges and peaks to the sparkling Tarija River below. The waters of the Tarija have a long way to go. The river will eventually drain into the mighty Paraná and the Atlantic Ocean via the Río Bermejo and the Río Paraguay. Up here in the high forest, the Tarija is intimate and beguiling. Sparkling rapids plunge into deep, mysterious pools, and every bend and riffle promises the chance of a truly monstrous specimen.

The Tariquía Reserve, through which the Tarija River flows, has been visited by anglers for around 30 years, particularly by fishermen coming from Argentina. Those early fishing trips into the reserve were clandestine and never officially authorized, but whispered rumors about the river’s incredible dorado circulated within the fishing community. For many years, Marcelo had heard that the Tarija River inside the reserve held exceptionally large golden dorado. He had also seen photographs over the years that seemed to confirm those stories, so he knew that there was potentially a very special fishery there.

In 2018, Untamed Angling formally presented their project to develop a legal and properly managed fishing operation in Tariquía. The environmental licensing and approval process was extremely complex, and it ultimately took Marcelo and his team around six years to obtain the necessary permits to begin operating. In September 2024, Marcelo made his first serious exploratory expedition. He accessed the area by helicopter, but once on the river, he was obliged to explore and fish entirely on foot.

That expedition confirmed not only what Marcelo had heard about the quality of the fish, but also what Argentine anglers had been telling him for years about how difficult the Tarija is to fish effectively.

It is a relatively large river—considerably bigger and more powerful than the rivers that Untamed pioneered and still fish at their Tsimane lodges on the upper Sécure River and its tributaries. The substantial volume of water and very strong currents mean that in many places it is difficult or impossible to wade across safely. The geography of the river also creates another problem: the productive runs and rapids are often separated by very long, deep pools.

Fishing those pools effectively from the bank is extremely difficult. Some stretches can be 50 or 60 meters wide, which means that with a fly rod the angler simply cannot cover much of the water from shore. Wading into the pool can disturb the fish, while in the faster sections, casting angles are often restricted by enormous rocks, steep terrain and vegetation behind the fisherman.

The solution was to use specially equipped NRS rafts, in much the same way that trout rivers are traditionally floated in places such as Patagonia and the United States: one guide rowing and two anglers fishing from the raft. This suddenly allowed anglers to cover water that was almost impossible to fish properly on foot.

The next step was incorporating the helicopter into the system. A helicopter not only provided access to this extremely remote section of the river, but it also allowed the ability to reposition the rafts upstream so that each new descent could begin again from the upper sections. Marcelo launched his program last year, and it is one of the most exhilarating fisheries that I have ever had the privilege to experience. 

At its heart, the Tariquía operation is built around three elements working together: helicopter access, helicopter-supported raft logistics, and fly fishing for golden dorado from purpose-built rafts. This logistical combination has almost certainly never been used before in this way—and certainly not for a golden dorado fishery.

From the standpoint of the fly-fishing operation itself, the fishing pressure is extremely low. Untamed operates only three rafts, with a maximum of six anglers fishing approximately 80 kilometers of river, and all fishing is strictly catch-and-release. At that level of use, the pressure created by the sport-fishing operation is minimal.

The much greater long-term challenge is protecting the river itself. Over the years, the Tarija has been subjected to increasing fishing pressure from people entering the reserve to harvest fish. Some are from nearby communities and others come from outside the area. As new access routes gradually appear, sections of river that were once naturally protected by their remoteness become increasingly vulnerable. The geography that makes the Tarija such an extraordinary river also makes it extremely difficult to protect. It is a remote, rugged environment, and effective enforcement across such a large area is a major challenge for SERNAP, Bolivia’s National Service of Protected Areas.

For that reason, conservation and surveillance have become an integral part of the project. Untamed Angling is working with local community members as territorial guards, supporting protection posts along the river, and is currently developing an agreement with SERNAP under which Untamed Angling would finance five park rangers year-round whose primary responsibility would be the protection of the river.

In Marcelo’s opinion, this is the most important part of the long-term sustainability equation. The objective is not simply to ensure that the anglers have a minimal impact. It is to use a very low-impact fishing operation to help create the funding, local involvement, and the permanent presence necessary to protect the river throughout the year. Ultimately, Marcelo believes that the measure of success will be whether the Tarija River is better protected because his project exists.

In order to sustain the fishery, Marcelo believes that it is crucial to understand the fish, notably their movement. Marcelo accepts that this understanding is in its infancy. Untamed only began operating in Tariquía in 2025, and the biological research on the river’s population of golden dorado is still at a very early stage. Marcelo is keen to assert that we must distinguish between what we know scientifically and what the river is already telling us empirically.

One of the most interesting questions is whether these fish are truly migratory or whether a significant part of the population is resident within the protected section of the Tarija River.

Downstream from the reserve, fishing pressure becomes extremely intense. Fish are harvested with nets and other methods, and there have even been reports of illegal fishing with explosives. Inside the reserve, by contrast, there are more than 120 kilometers of river offering a very different environment and a substantial refuge from that pressure. For that reason, Marcelo’s working hypothesis is that many of the large dorado that have been encountered in the Reserve are largely resident within this protected section of the river, moving within it rather than making extensive migrations downstream. However, Marcelo is very keen to emphasize that this is still a hypothesis based on observation and experience, and not (yet at least) a scientific conclusion.

He notes that he has witnessed something that may be analogous in another dorado fishery that he knows extremely well. At La Zona, below Salto Grande Dam on the Uruguay River, where Marcelo began working in 2001, extraordinary numbers of very large dorado concentrated within a one-kilometer-long exclusion zone immediately below the dam. Just 15 kilometers downstream are the cities of Concordia in Argentina and Salto in Uruguay, where the fish historically faced much greater fishing pressure. Over time, Marcelo observed large dorado using that very small protected area not simply as a temporary refuge, but as habitat where they could feed and remain for extended periods. Dorado are remarkably adaptable fish. Marcelo’s experience over many years has shown him that when they find habitat that provides food, suitable conditions, and protection from intense fishing pressure, they can make extraordinary use of relatively limited areas. 

That is why Marcelo believes something similar may be happening on a much larger scale in Tariquía. Instead of a refuge measuring roughly one kilometer, these fish have more than 120 kilometers of protected river available to them. The next step is to move beyond empirical observation. As the biological work develops, Marcelo wants to understand their movements scientifically and determine whether there is a predominantly resident population, a migratory population, or—as is entirely possible—a combination of both behaviors. One thing that is very important to Marcelo is the involvement of the local communities.

There are 24 communities within the area, and the Tariquía project was approved by an overwhelming majority of them. For every visiting angler, the operation generates a $600 USD community fee that goes directly to those communities. This means that the presence of a small number of international anglers creates a direct economic benefit for the people who live in and around the reserve. Local residents are also employed in different aspects of the operation, including looking after the rafts, working as territorial guards, and performing other logistical and operational roles.