A few footsteps from the vast, peaceful waters of the Tapajós River, far beneath the canopy of the untamed jungle, Juarez Saw Munduruku hacked at the dense bracken with his 18-inch hunting knife.

The 55-year-old leader of the Munduruku, an Amazon tribe, was marking its territory. For centuries the clan, known as the “red ants” for their deadly mass assaults on rival tribes and colonialists alike, would do so by placing the severed heads of their adversaries on spikes. Now, his men hammer handmade wooden signs with words in their native language stenciled in red paint onto tree trunks.

The meaning, however, is still unmistakable: This is Munduruku land.

The signs are man-made specks in an ocean of nature but are harbingers of a battle to come. It is a fight between the Munduruku, who have long sanctified this river, and Brazil’s government, which plans to flood much of this land to build a $9.9 billion hydroelectric dam, the São Luiz do Tapajós. The dam is one of seven planned for this river and part of a wider strategy across the Amazon that the energy ministry says is necessary to sate the country’s growing need for power. But the Munduruku say they have a constitutional right to remain on their territory — and that the government is refusing to acknowledge it, in violation of the law.

The battle echoes the government’s fight with indigenous communities on the Xingu River, another major Amazon River tributary, over the Belo Monte Dam. That project, first conceived in 1975, is now nearing completion. But environmental activists say that while the tribes there were ultimately divided — and defeated — by threats and bribery, the Munduruku have the determination and unity to take on the government and win.

The red signs are a start. They are part of a broader plan to protect the land that the Munduruku, who number 13,000 and live in a series of villages on the river, say they will, if necessary, defend to the death.

“We will fight to the end,” said Juarez Saw Munduruku. “This is our struggle. … I would die defending my land so that another generation can live here.”

According to Munduruku legend, the first member of the tribe, named Karosakaybu, was born from the seed of a tucumã palm tree in Sawré Muybu, the area under threat from the São Luiz do Tapajós dam. He created the men, women, animals and the river Tapajós itself. The river is interwoven into the fabric of the tribe’s identity. It is their home, their transport, their food, their drink, their bath and their graveyard.

For centuries the clan frequently clashed with other tribes on the Tapajós, gaining a reputation for ferocity in battle. Later, the Munduruku successfully fought Portuguese colonialists who aimed to take their land and enslave their tribesmen.

The first documented evidence of the tribe came in the early 1770s, “when they began to systematically attack the Portuguese situated along the banks of the Amazon river,” according to a report by Brazil’s National Indian Foundation, or FUNAI. The tribe itself says the Governo Karodayri — the leadership of the Munduruku — may have existed before the Portuguese arrived in 1500.

As tribal leaders admit, the Munduruku simply like a good fight.

Today, the tribal land known as Sawré Muybu is home to a straw-roofed village of 136 people, accessible only from a jetty off the main river amid mist-filled trees and a chorus of mosquitoes. Centuries of know-how help the Munduruku stay alive in one of the most dangerous parts of the forest, filled with jaguars, snakes, alligators and scorpions.

Each morning, they hunt tapirs, monkeys, deer and armadillos with arrows and knives to be skinned and roasted the same day. At the village schoolhouse, the children are taught subjects including Portuguese and the Munduruku dialect, which was, for most of its history, only a spoken language. A soccer pitch sits amid the forest.

The villagers bathe in a brook off the main river. Surrounded by splayed tree roots, hovering butterflies and the distant chirping of birds, children play with abandon while women wash pots and pans and the carcasses of dead animals. The water turns from turquoise to emerald where the sun shines through the lattice of the tree branches. At night, alligators and anacondas sleep here.

Brazil has a population of just under 900,000 Indians, according to the most recent census. The country’s democratic constitution, passed in 1988, recognized their traditional territories and gave protected status to indigenous lands — which are currently estimated at 412,000 square miles, 12.5 percent of Brazil’s territory.

To award protected status, FUNAI spends years conducting research on tribal lands, interviewing locals and examining documents. If the agency finds that the land has historical links to indigenous people, it releases a study, known as a demarcation report, which then needs a sign-off from the president. Once lands are demarcated, it is unconstitutional to remove indigenous people from those territories except “in the case of a catastrophe or an epidemic.”

But under President Dilma Rousseff, this approval process has slowed to a trickle. Indians complain that she is under pressure from farmers and landowners, lobbies that have consolidated their influence over Congress in recent elections. A proposed constitutional amendment, championed by politicians linked to farmers, would shift the ultimate power to demarcate to Congress, a body likely to be less sympathetic to the rights of Indians. In similar cases elsewhere in Brazil, farmers and other landowners face losing their land if it is deemed to be indigenous.

“The demarcation process has been derailed by political interests,” said Maria Rachel Coelho Pereira, a law professor in Rio de Janeiro who studies indigenous rights. “Now Indians across Brazil are worrying if they will ever receive the land rights they were rightfully granted by the constitution nearly 30 years ago.”

FUNAI completed a demarcation report on Sawré Muybu in September 2013, but the document has yet to be published in an official gazette, a prerequisite for the process to proceed. A copy of the report, obtained by the Brazilian investigative journalism agency Agência Pública, revealed it ruled in favor of demarcation.

The report said the Indians may have occupied the middle Tapajós before the 19th century and perhaps even before the Portuguese conquest in 1500. “If the indigenous peoples are to be given the legal security to which they are entitled and to have their other rights fully respected, it is essential that the state recognizes the indigenous territory of Sawré Muybu,” the report concluded.

The Munduruku have accused the federal government of stalling the release of the report because of its implications for the mammoth São Luiz do Tapajós dam. The 8,040-megawatt plant, which would be one of the largest in the world, would radically remake the landscape by flooding much of Sawré Muybu. Of the seven planned on the Tapajós, it is by far the biggest and most controversial. Others would also affect the Munduruku and other indigenous tribes.

In a meeting in September, tribal leaders confronted Maria Augusta Assirati, then the president of FUNAI, about the organization’s failure to protect their tribal lands. She admitted that the hydroelectric plans were the main impediment to demarcation. “I think this indigenous land should have been demarcated. The report should have been published, but that does not depend on the will of one organization,” she said, before breaking down in tears when the tribal leaders suggested she resign. Nine days later, she left her role.

FUNAI and Assirati did not respond to requests for comment.

Soon afterward, Brazil’s Ministry of Mines and Energy suspended a December 2014 auction of the contract to build the São Luiz do Tapajós dam. But the agency has since stated that it expects to proceed with the auction by the end of this year.

In March, federal prosecutors, who enjoy significant independence from other government agencies, filed a lawsuit to force FUNAI to publish the report about Sawré Muybu, saying the agency had missed a legal deadline to do so.

“It is clear there has been an unfortunate reversal of values in the Brazilian state,” said prosecutor Camões Boaventura. “Only in a country where laws are disposable, such as in Brazil, would a constitutionally guaranteed right be simply neglected in the face of interference from political and economic interests.”

On April 30, a federal court ruled in favor of the prosecutors. Judge Ilan Presser ordered FUNAI to release the report within 15 days or face a daily fine of $990. It also ordered the agency to pay $6,590 in damages. However, FUNAI has still not been officially notified of the decision.

The ministry says a new generation of hydroelectric plants, which already supply more than 75 percent of Brazil’s energy, are crucial in maintaining the country’s status as a leader in clean, renewable electricity and preserving energy independence. The plans have “respect for the environment and population,” it added. Environmentalists cede the importance of clean energy but say the government’s plans threaten ecosystems and fish stocks and will destroy swaths of forest.

With his hunting knife, Juarez Saw Munduruku slowly but surely cut a path through the rain forest. For weeks he had been working with his men to do what the federal government had refused to do: demarcate the 687 square miles of their tribal lands.

A tribesman with a GPS device led a team of 20 other men armed with scythes to ensure that the route would match exactly that decreed in the FUNAI report. They cut through the forest and then marked the border with a latticed wooden fence. The demarcation was also intended to protect the land from poachers, who steal their crops of açaí and palmito, and from illegal prospectors, who scavenge for gold.

Back at the village, Juarez Saw Munduruku was dressed in war paint made from the genipapo fruit and wore a headpiece made from orange macaw feathers. In his soft, lilting accent, he explained a parable about the tortoise — an animal held in high regard by the Munduruku, whose war paint resembles its shell markings — that has been recounted by tribal elders for generations.

The parable tells the story of how the tapir, a piglike mammal, used his brute strength to bury the tortoise in mud. But the tortoise escaped, then waited patiently to exact his revenge. When he saw the tapir sleeping with his testicles exposed, the tortoise bit the tapir — and wouldn’t let go. “Just like the tortoise, we can creep up on the government and bite its balls,” said Munduruku, the tribal chief.

“We Munduruku will stop this dam,” he continued. “Now we are fighting with documents. If the government insists, if it sends in the National Force, then we will fight with bodies. Everyone has made the decision, no one will give up.”

“To them, the Tapajós is the equivalent of the Vatican for the Catholic Church,” said Danicley de Aguiar, a Greenpeace campaigner in the Amazon who works with the Munduruku. “They are hunting the government, looking for the weak spot, and it is the government who are scared. Do they have the courage for bloodshed?“I have been in the Amazon for 20 years and I have never seen anything like it. They are going to win. I believe they will exist for another 500 years.”

If the dam proceeds, the affected villagers would be offered housing elsewhere, something they are determined to reject. The ministry says it is always “open for dialogue” but would not comment on the potential for conflict.

Environmental activists hope that São Luiz do Tapajós will not follow the same course as the Belo Monte, the Xingu River dam that is now nearly complete. Some tribal leaders opposed to that dam were bought off by the government, according to Maíra Irigaray, the Brazil coordinator of the group Amazon Watch. She fears similar tactics will be used here.

“Leaders were paid off with boats, cars, cash and bodyguards,” she said. “If the leaders took the money, the government won. If the leaders didn’t take the money, [contractors and others involved in dam construction] would spread lies and still manage to break their trust with the community.”

The ministry says such claims of bribery are “totally absurd” and false.

The Munduruku, meanwhile, say they will not succumb to bribes or threats of violence. In 2013, the tribe captured three biologists who were in the region doing a study ahead of the environmental licensing — one of a series of regulatory stages in the development of the dam. They were held for 48 hours until the government promised to suspend the study.

“They kept them in a cage and threatened to burn them alive unless the government explained what they were doing on indigenous land without consent,” Irigaray said. Now federal forces accompany any such mission to the region.

For Luzia Puxu, 80, the oldest of the Munduruku on this part of the river, moving was not an option. “For us the river is everything,” she said. “Without it we can’t drink, can’t bathe, can’t fish.” Speaking in a frail voice in her native language, she added, “I don’t want any house that they will offer me to move. I want this house.”

As the day ended and blackness enveloped the river, shards of golden lightning struck beyond the silhouetted forest on the far bank. War is coming to the Tapajós, and not for the first time. The Munduruku are ready.

(Photography by Mauricio Lima)