Crashing upstream through the São Luiz rapids, the churning river throws the speedboat around like a child’s toy. There is first a moment of fear, then relief and finally wonder at crossing a natural boundary that has held back the destruction of this corner of the Amazon for almost five centuries.

This is the gateway to a land that indigenous inhabitants call Mundurukania, after their tribe, the Munduruku, which has settled the middle and upper reaches of the Rio Tapajós since ancient times. The thickly vegetated shores, misty hills and untamed waters – breached at one point by a dolphin – mark it out as one of the few regions of the planet still to be explored and exploited by industrial commerce.

The tranquillity is breathtaking, but misleading. These rapids are now on the frontline of one of the world’s most important struggles for indigenous rights and environmental protection. Long ignored, they are suddenly seen as a stategically crucial step between the nations with the world’s biggest farms – Brazil – and the world’s most numerous dining tables – China. Longer term, the changes now being planned could bring this waterway closer to the industrialised, traffic-filled Yangtze in more ways than one.

Over the coming years, the Brazilian government – backed by Chinese and European finance and engineering – wants to turn this river into the world’s biggest grain canal by building 49 major dams on the Tapajós and its tributaries.

This would make the rapids navigable by barges carrying produce from the deforested cerrado savanna of Mato Grosso – which produces a third of the world’s soya – up to the giant container port being planned in the closest city of Santarém and then out to global markets, particularly in Asia.

The network of dams would also produce 29gW of electricity, increasing Brazil’s current supply by 25%. A consortium headed by Furnas – a subsidiary of the state-run energy utility Electrobras – plans to sell the power to distant cities and to local mining companies that want to unearth the mineral riches under the forest.

For the Brazilian government, this mega-scheme to open up the Tapajós basin – which is roughly the area of France – is a linchpin of national economic development and trade with China. For local politicians, it is an opportunity to industrialise, expand and enrich the business of nearby cities, which expect their populations to double in size over the next 10 years.

For opponents, however, the “hydrovia” – as the river transport scheme is known – and related projects are the biggest threat ever posed to the native inhabitants, traditional riverine communities, waters and wildlife. By one estimate, 950,000 hectares of forest would be cleared, releasing significant amounts of carbon dioxide.

“The hydrovia is part of a set of other projects – dams, ports, roads and railways – that aim to industrialise this region. Energy companies, agribusinesses and mining companies are all pushing for it,” said Fernanda Moreira, of the Indigenous Missionary Council, a Catholic NGO that works with local communities.

Campaigners – including International Rivers, Amazon Watch and Greenpeace – oppose the project because they say there has not been adequate study of the impacts – including accelerated deforestation, habitat loss and social problems – or the alternatives.

The government will have to kill us if they want to push ahead with these projects Munduruku village chief Juarez Saw Munduruku

“This is a historic moment for the Amazon. We have seen previous economic booms – rubber, logging and mining – that caused social conflict and environmental damage, but the proposed development along the Tapajós covers a much wider area and would have a much more profound impact,” said Alcilene Cardoso of the Amazon Environmental Research Institute.

Opponents claimed a partial victory last year when the Brazilian environmental agency suspended a licence for the São Luiz do Tapajós dam, one of the three biggest hydroelectric plants in the project that would together flood 198,400 hectares, including large parts of national parks, nature reserves and territory claimed by indigenous groups.

The battle is anything but over, however. The damming of the rapids – which would require a 7km-wide concrete barrier and a reservoir eight times the area of Manhattan – remains a priority of the powerful mines and energy ministry and Electrobras. Three other dams are already under construction on the Teles Pires, a tributary of the Tapajós.

Munduruku efforts to assert their territorial rights through a self-demarcation campaign have been ignored by the centre-right government of President Michel Temer and his Workers’ party predecessor, Dilma Rousseff.

Half an hour above the rapids is the Munduruku village of Dace Watpu, which would be flooded if the São Luiz dam were built. Despite the suspension of the licence, they remain vigilant.

“They will be back. That is our constant concern,” said village chief Juarez Saw Munduruku, as residents gathered in the small wooden hall to celebrate the fifth anniversary of the community school. As the school, the two-way radio and array of solar panels demonstrate, the villagers are not opposed to development – but they want it to be on their terms. Dams, mines and river traffic, they say, are a threat to their homes and way of life.

“The Brazilian government may call hydroelectric dams clean energy, but it isn’t. It is dirty. It is mixed with our blood and our misery,” he says. “The government will have to kill us if they want to push ahead with these projects.”

Images of Munduruku protests usually show them in traditional costume, with warpaint and feather headdresses. But their strategy is more sophisticated than these images suggest.

Recognising that foreign investment and consumption are part of the issue, they have taken their campaign overseas, presenting their grievances last month at the United Nations. They have also worked with environmental NGOs, foreign media and archaeologists.

The latter have verified the long history of settlement in the region, which is crucial to Munduruku ownership claims and also important to rebut the widely held idea that this region can be dammed because it is empty. The first written record of “Mundrukania” dates back to 1742, though habitation by indigenous groups goes back much further.

When Bruna Rocha, of the Federal University of Western Pará, first excavated sites near the proposed dams in 2010, she found pottery, stone tools and dark earth, suggesting cultivation of the land had occurred intermittently for many centuries. “Studies of the area showed it wasn’t just an empty space that can be flooded. It has history and a culture,” she said.

Facebook Twitter Pinterest The Munduruku tribe protest in front of the Palace of Justice in Brasília last year. Photograph: Andressa Anholete/AFP/Getty Images

The image of the Amazon as a wilderness was a construct of 19th-century Europeans, which has been adopted on several occasions by Brazilian governments: first during the dictatorship era to justify a land distribution and road-building policy, and most recently by successive administrations to back up the argument that dams will not have much of a social impact.

“The prevailing view is that the Amazon is a provider of raw materials rather than a centre of culture. That is wrong,” Rocha said. “In the 16th century, several million indigenous people lived in the Amazon and they had a standard of living that was higher than in Europe at the time. But about 90% were wiped out by the guns and diseases of the colonisers.”

The Munduruku survived thanks to the rapids – which prevented steamships from entering their territory – and temporary alliances with European settlers against other tribes.

Now, they are changing strategy, linking up with the nearby riverine community of Montanha e Mangabal – most of whose inhabitants are former rubber tappers - to oppose the project. “In the past, we used to fight one another. But that is finished. Now we must unite against a common and powerful enemy: the government,” says Juarez Saw Munduruku. “The more people are involved in the struggle the better.”

Maurício Torres, a geography professor at Federal University of Western Pará, said the alliance marked a turning point. “Two generations ago, the indigenous communities and the rubber tappers were fighting one another. Now they are united against the dam and have delayed the process of approval. That is remarkable.”

But they are up against enormous geostrategic pressures. To lift Brazil out of recession, the government wants to ramp up exports of soya and meat, particularly to Asia. Currently China accounts for 57% of Brazil’s overseas soya sales and production and demand are expected to grow.

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“We have opened the biggest food frontier in the world,” said Roberto Jaguaribe, a former Brazilian ambassador to Beijing who is now head of the state’s export promotion body Apex-Brasil. “The Food and Agricultural Organisation expects global demand for food to rise by 30% over the next 20 years. To cope, Brazil needs to increase production by at least double that average.”

Due to environmental pressures in China – particularly water shortages – Jaguaribe says it will become “rational” for Beijing to import more meat and grain from the farms and ranches of Mato Grosso. A Tapajós hydrovia would facilitate this. Little wonder, then, that among the construction companies aiming to provide finance and support to Furnas for dams on the Tapajós and Teles Pires is the Three Gorges Development Corporation, which built the world’s biggest hydroelectric plant on the Yangtze. French, Spanish and Italian energy firms are also involved.

Politicians in the Amazon go further, saying they hope the hydrovia will act as a catalyst for industrialisation. “We are in the midst of several huge projects of national strategic importance, but we don’t want to be a mere corridor for soya to reach the world market. We want to build food factories here. We want more fish farms in our rivers,” said Nélio Aguiar, the mayor of Santarém. “We hope the Chinese investment is important for that.”

Thanks to a surge of development, this city – which sits on the confluence of the clear Tapajós and cloudy Amazon – is thriving. Last year, it bucked the recession that afflicted the rest of Brazil to rack up impressive growth. The world’s biggest agricultural company – Cargill of the United States – recently built a huge new grain terminal here. The municipal government is planning an even bigger container port.

“Many investors want to come here. We are the last frontier,” said the mayor. “In the next 10 years, we project Santarém will double its population from 300,000 to 600,000 and the city will be more prosperous and offer a better quality of life.”

He has support from the Nature Conservancy, which backs plans for a dam cascade to provide energy and food to a growing global population. “The Tapajós river is important to not only its surrounding lands, wildlife and people, but also to the entire Brazilian population and to the world,” the US-based group notes.

Certainly, an infrastructure upgrade is essential. The main road between Mato Grosso and Santarém – the BR163 – has recently become so choked with soya trucks that it has begun to challenge China’s worst coal transport routes for the unwelcome title of “world’s worst traffic jam”. Earlier this year, after rains turned the dirt into mud, trucks were snarled up for 10 days over a stretch of more than 50km, forcing the authorities to organise emergency provisions of food and water to trapped drivers.

Facebook Twitter Pinterest The São Manoel dam site on the Teles Pires, a tributary of the Tapajós river in the Amazon. Photograph: International Rivers

How to ease this bottleneck is a question of global importance. There are three approaches: an upgrade of the BR163 (which would make it wider and paved in asphalt), a parallel Ferrogrão grain railway (also financed by China and supported by many environmentalists as a lesser evil in terms of pollution and traffic), and the Tapajós hydrovia (which is preferred by grain companies, construction firms and electricity utilities). Rather than choosing one of these options, the national government is pushing all three at once.

“This is the fastest development I’ve seen since I arrived in Santarém 30 years ago,” said Caetano Scannavino of the Saúde and Alegria (Health and Happiness) NGO. “But it’s not planned. They are repeating the errors of the past.”

Some fear that this will lead to the industrialisation of the Amazon as forests are cleared, traffic increases, factories move in and the population surges to the point where the Tapajós begins to resemble the stressed and polluted Yangtze. Adding to these fears, the Temer government recently submitted a bill to congress that would reduce the size of the nearby Jamanxim national park by 350,000 hectares, or 40 times the area of Manhattan.

The Amazon Watch NGO recently urged the government in Beijing to rethink its use of the Brazil-China Cooperation Fund to finance destructive transport projects in sensitive ecosystems.

“Support of projects that result in rainforest destruction undermines China’s efforts to position itself as a leader in the global fight against climate change,” the group’s program director noted.

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In Itaituba, the town closest to the proposed site of the São Luiz dam, officials express similar concerns. The town – which has previously seen booms of gold mining, logging and timber – is in the midst of a new expansion due to its location as the first port below the rapids. Cargill, Bunge and four other companies have built huge terminals, which transfer grain from trucks on the BR163 to barges on the Tapajos. More are expected. On a recent afternoon, a group of Chinese businessmen – all wearing black suits and lapel pins showing the flags of the two countries - were visiting the town to look into a possible purchase of land for a port.

Bruno Rolim, secretary of the environment in the municipal government, was wary. “China has lots of pollution accidents. It suggests they put much more of a priority on the economy than the environment,” he said. “This is a very sensitive area. The Amazon has the greatest freshwater assets in the world. We don’t want what happened [in China] to happen here.”

Domestic precedents also give him cause for concern. The last huge Amazonian dam – at Belo Monte – has caused enormous social and environmental problems since it was completed in 2015.

The population of nearby Altamira has surged without adequate provision of sanitation, hospitals and education. Crime, suicide rates and deforestation level are among the highest in Brazil. The project has also been a focus of a massive corruption scandal involving construction companies and politicians.

“We saw what happened in Altamira,” Rolin said. “Big projects in the Amazon have not benefited local people. They extract power or commodities for other regions and countries and leave problems behind. The negatives are greater than the positives.”

Given its history as a centre of illegal mining and logging, however, Itaituba is probably not a city that environmentalists or indigenous campaigners can rely on.

At the municipal museum, the curator and founder, Regina Lucirene Macedo d’Oliveira, said this was a region where people have always just taken what they can rather than investing in making it a better place. “The local government turned a blind eye when rubber tappers destroyed the forest. They did the same when the gold miners contaminated the rivers. With each economic boom, they promise to regulate and protect, but they do nothing. Why should it be any different this time with the big hydro projects?”

For now, the dire state of Brazilian public finances and local opposition are holding up plans to dam the São Luiz rapids. But in the long term, it will be hard to resist Chinese money, the politically powerful agribusiness lobby and a global economic system geared towards consumption growth. The Yangzification of the Tapajós is a distant but entirely possible prospect.

The Munduruku are under no illusions, but they say they will fight to preserve the rapids that have kept them secure until now. For them, it is about conserving their home – a lesson, they say, the rest of the world should learn.

“We protect the gateway. If they build the dam, it will kill the Munduruku,” said Valto Dace, the head of the Dace Watpu village. “We will not move. God gave us this land. Where would we go?”