Science & Nature

A river’s pulse: Indigenous people and scientists unite to track giant dam’s environmental toll

A river’s pulse: Indigenous people and scientists unite to track giant dam’s environmental toll thumbnail

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A version of this story appeared in Science, Vol 379, Issue 6627.Download PDF

This story was produced with support from the Rainforest Journalism Fund in partnership with the Pulitzer Center. It is also available in Portuguese.

Soon after sunrise one warm day in September 2022, 26-year-old Josiel Pereira Juruna boards a small motorboat and sets out on the emerald-green waters of the Xingu River in the Brazilian Amazon. Accompanying him are biologist Cristiane Carneiro and Pedrinho Viana, a fellow fisherman from their village of Muratu in the Paquiçamba Indigenous Reserve in northern Brazil’s Pará state. After a short ride, Viana hauls in a gillnet set out in a creek the night before.

He pulls a disk-shaped fish with bright gray scales and a yellowish belly from the net and hands it to Josiel, who hangs it from a portable scale. “One hundred and fifty grams,” he declares, then presses a ruler against the animal, known as a big-eyed pacu. “Fifteen centimeters,” he says, as Carneiro takes notes.

It’s a ritual of weighing and measuring that Josiel has performed nearly daily for the past 3 years to monitor the river’s fish stocks. Of all fish in this stretch of the Xingu, the seven species of pacu are the most important for his community, the Juruna, who rely on fishing for food and income. Known as vegetarian piranhas, pacu can reach up to 1 meter long. But they are dwindling. In November and December 2014, the best fishing months of that year, fishermen in Muratu caught a total of 770 kilograms of pacu. Over the same months in 2021, that number dropped to 175 kilograms.

“Now we only catch very skinny and small pacu, almost without fat,” Josiel says with disappointment as he gestures to the specimen in his hand.

Indigenous researchers capture pacu

an Indigenous researcher takes some measurements from a pacu

Indigenous fisherman Pedrinho Viana retrieves pacu from a gillnet set in a creek in the Xingu River (first image). The fish, one of the most important for the Juruna people, has been getting smaller and scarcer in the region since the dam’s construction in 2016. Josiel Juruna weighs and measures a small pacu netted in the Big Bend of the Xingu River (second image). Species of pacu can get as long as 1 meter. Dado Galdieri/Hilaea Media

The likely cause lies 30 kilometers upstream of Muratu: the largest hydroelectric project in the Amazon basin, a complex of dams, reservoirs, and power stations known as Belo Monte. The project was originally slated for construction in 1975, but years of protests from Indigenous communities and a lack of investment stalled it. In the 2000s, after major electricity blackouts in the country, President Luiz Inácio “Lula” da Silva (recently reelected) pushed for the project, despite international opposition from environmentalists and scientists, and it began operating in 2016.

The main dam, called Pimental, had a dramatic impact on the river, creating a 359-square-kilometer reservoir and diverting much of the Xingu’s flow northeast through a 17-kilometer canal to a secondary reservoir and hydroelectric station. Downstream, along the 130-kilometer river stretch called the Big Bend of the Xingu, the diversion reduced the river’s flow by up to 80%. It also interrupted the river’s annual cycle of flooding, crucial to its rich biodiversity.

The Juruna call 2016, the year the main dam was completed, “the end of the world.” The impacts were evident right away, when an abrupt release of water from the dam killed 16.2 tons of fish. The Brazilian Institute of Environment and Renewable Natural Resources (IBAMA) imposed a fine of 35.3 million reais ($6.6 million) on Norte Energia, the company that runs the hydroelectric project. Josiel and other people from the Paquiçamba reserve were not surprised at the havoc. “The elderly in our villages knew we would have this kind of problem with the dam,” Josiel says. “We knew the fish would suffer with a river flow that is no longer natural.”

The Pimental Dam at the Belo Monte hydropower project

Pimental, the main dam of the Belo Monte hydropower project, diverts 80% of the Xingu River’s water to an artificial channel, which sends it to a secondary reservoir and power-generating turbines.Dado Galdieri/Hilaea Media

They had already asked researchers to help them document the changes. In 2013, with the support of a local nongovernmental organization known as the Socio-Environmental Institute, the Juruna established a partnership with an informal network of scientists from public universities across Brazil. Among them was Carneiro, who was doing a Ph.D. in ecology at the local Federal University of Pará (UFPA), Belém. Together, the Juruna and the scientists have been recording change in the abundance, habits, and size of the fish and turtles living in the changed river.

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For Philip Fearnside, a biologist at the National Institute of Amazonian Research (INPA), the collaboration “is essential to show the huge impact instead of simply accepting it.” Fearnside, who isn’t involved in the collaboration but has been studying dams in the Amazon for more than 30 years, says partnerships between Indigenous people and researchers are critical in Brazil, where government approvals to build and operate dams are often “a token gesture,” and companies “can go ahead and build the dam anyway,” regardless of impact.

a map showing fish breeding sites along the Xingu River and the Belo Monte plant

K. FRANKLIN/SCIENCE

In a statement sent to Science, Norte Energia said changes in Xingu fish populations are within the range of what was predicted in the environmental impact studies conducted before the dam’s construction. But the full scope of those impacts is emerging in the data the Juruna and their scientist collaborators have collected. Their findings have been published in peer-reviewed journals and used to fight for reparations and for the dam’s operators to restore some of the river’s natural flow.

Now that Lula is once again president, after campaigning on promises of a strong environmental agenda and plans to create an Indigenous Ministry, the Indigenous people and their scientist allies hope their findings will lead to permanent changes at Belo Monte—and in the hundreds of other dams being planned or built in the Amazon. “I think things will get better for Indigenous peoples during this government and maybe more water will be released to the Big Bend,” Josiel says. “That is what I hope for.”

a Juruna woman paints Janice Cunha during a meeting

a Juruna indigenous woman painted for a dance

A woman from the Juruna community applies ceremonial paint to biologist Janice Muriel Cunha (second from right, first image) during a September 2022 meeting to discuss research ties between Indigenous people and scientists. A Juruna Indigenous woman wears traditional paint for a dance in the village of Muratu (second image). DADO GALDIERI/HILAEA MEDIA

BEFORE THE DAM, the Juruna—and the fish— could count on the river’s seasonal rhythm. During the rainy Amazonian winter, from December to May, as much as 20,000 cubic meters per second of water surged down the river, overflowing its several channels and spilling onto islands and adjacent forests. In the summer the flow falls as low as 2000 cubic meters per second. Over millennia, this flood pattern has shaped the river’s landscape and species.

Now, the dam has cut the winter flow by more than half. Worse is to come: a new flow regime that in alternate years will reduce the maximum winter flow by another 50%, to one-fifth the natural level. (IBAMA had approved the plan, but until recently courts had blocked it.) Because of the water diversion, “The cycle of the flood pulse, the most basic characteristic of that ecosystem, was completely altered,” says Camila Ribas, an INPA biologist who collaborates with the Indigenous peoples. “If you change this, you change all the relationships within this system and may permanently destroy it.”

A weakened pulse

In natural conditions, the Xingu River has a high volume during the Amazonian “winter” (December to May) and a low volume in the summer. But the construction of the Pimental Dam drastically reduced the water flow. (Hydrograms A and B represent alternating flow regimes.) In 2019, the government temporarily forced the dam to release more water. Now, scientists and the Juruna community have proposed increasing the flow to minimize environmental damage in the river.

graph showing water flow change in the Xingu River
(GRAPHIC) K. FRANKLIN/SCIENCE; (DATA) BRAZILIAN NATIONAL AGENCY OF WATERS, ANALYZED BY ANDRE SAWAKUCHI/FEDERAL UNIVERSITY OF SÃO PAULO

The Juruna and their scientist partners have been monitoring the consequences. Outside researchers trained 12 people from the Juruna community to conduct the work. Every day since the project began in 2013, one of them is tasked with recording the weight and length of individual fish, as well as the total amount of fish caught in the reserve.

More recently, the Juruna also started to investigate how the change in the river flow has affected fish breeding sites in the igapós (from the Guarani language for “root forests”), the seasonally flooded forests on the river margins and islands. For multiple species of fish and turtles, these forests are vital habitats. Pacu, matrinxã, curimatá, and other local fish feast on ripe fruit that falls into the water from the trees, a bounty that includes the tiny red cherrylike sarão (Myrciaria dubia), the yellow plum-shaped cajá (Spondias mombin), and the round seringa, the fruit of the rubber tree (Hevea brasiliensis).

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In 2019, Josiel and a team of researchers from UFPA installed flood gauges on Zé Maria, a forested island 4 kilometers from Muratu village. Every November before the dam was built, the rain-swollen Xingu would slowly advance over the island’s sandy beaches, reaching the top of its trees in April. The island remained submerged in up to 30 meters of water for the next 6 months, bringing an abundance of fish to feed and spawn. Now, even in March, Josiel can stand on the island’s leaf-littered ground. The instruments have never measured more than 2 meters of water.

a Juruna Indigenous researcher shows the last actual measurements taken at a fish nursery spot

Before the dam’s construction, the Xingu River often flooded Zé Maria island to depths of tens of meters, creating feeding and breeding grounds for fish. Last winter, a flood gauge placed by Indigenous researchers recorded a much-reduced flood.Dado Galdieri/Hilaea Media

Up to 70% of the Big Bend’s seasonally flooded forests no longer flood under the current water regime, according to data from Norte Energia. Other Amazon dams likely have similar impacts. Although Brazil requires environmental assessments for dam projects, the laws don’t specifically mention flooded habitats such as the igapós. “Our legislation has not kept pace with the scientific knowledge,” says Andre Sawakuchi, a geologist at the University of São Paulo’s main campus who is involved in the effort with the Juruna. “Igapós are forests inside the river. If you lose them, you cannot just replant. You cannot replant a river.”

Without a place to spawn, fish have been found with dry eggs inside their bodies “like dead babies inside a woman’s belly,” Josiel says. The fish have also lost an important source of food. “The fruits now fall onto dry ground, and the fish cannot eat,” Josiel explains. “It is very sad.”

The resulting decline of the Big Bend fisheries has hit the Juruna hard. “Before [the dam], we could fill three coolers of 160 liters with fish in a week,” remembers Maria das Graças, a Juruna fisherwoman and Viana’s wife. She and her husband raised their three children on fish from the Xingu. What the family didn’t consume, they used to sell. “Now, we go out fishing for 10 days and can barely fill two coolers.”

The data collected by the Juruna have quantified the change. Sent to researchers at UFPA for further analysis, the findings have led to academic papers on Xingu ecosystems and changes in Indigenous ways of life, and have gone into monthly reports presented in open meetings in the villages.

Juruna free divers compare the size of two acari-zebras

The acari-zebra, unique to the Big Bend of the Xingu, already faced pressure from collectors serving the aquarium trade. The dam and its impact on the river could be the last straw.Dado Galdieri/Hilaea Media

A separate study published in Science of the Total Environment in September 2022 confirms the Juruna’s observations. The research, partially funded by Norte Energia and conducted with data the company was required to collect, found a 29% decline in the number of species and a 9% drop in the abundance of all fish in the Big Bend. The decline was sharpest for pacu. The results are just the beginning of a “tragedy” that will worsen, says Kirk Winemiller, an ichthyologist at Texas A&M University, College Station, and an author of the study, because “we are only looking at the very early signs” of the dam’s impact.

Winemiller thinks some species may face extinction. The catfish acari-zebra (Hypancistrus zebra), a match-size fish with black and white stripes only found within the Xingu’s Big Bend, is one of his biggest worries. Illegal fishing for the aquarium trade had already depleted it, and in 2022 the International Union for Conservation of Nature declared it critically endangered because of the dam.

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THE COLLABORATION’S FINDINGS are already having an impact. The data are often sent to IBAMA—and the Brazilian Federal Public Prosecutor’s Office, which has filed several lawsuits against Norte Energia. Some accuse the company of “ethnocide,” the crime of destroying Indigenous cultures, because of the severe impacts of the dam on their lives.

In its statement to Science, Norte Energia said it has compensated the communities. New fish farming tanks installed in Indigenous villages have provided 660,000 reais ($124,000) in income to local families since 2019, the company says. In November 2022, the company also agreed to pay an undisclosed sum in reparations to about 2000 local fishermen. IBAMA had ordered this compensation as a condition for renewing the dam’s operating license.

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Canoes navigate past the Paquiçamba Indigenous reservation while some tribespeople dance to wish them luck

Indigenous peoples from the Paquiçamba Indigenous Reserve, dressed for a ceremonial dance, welcome a group of researchers arriving in canoes.DADO GALDIERI/HILAEA MEDIA

the Juruna tribal chief pauses in from of the sacred Jericoa waterfalls

Giliarde Juruna, chief of the Muratu Indigenous village, at the sacred Jericoá waterfalls in the Xingu RiverDADO GALDIERI/HILAEA MEDIA

Juruna people eat pacu fish and manioc flour during a break

Pacu fish and manioc flour are staples of the Juruna people.DADO GALDIERI/HILAEA MEDIA

a Juruna man looks on as other researchers install their hammocks

Didi Juruna bathes in the Xingu River near where he and other Indigenous river monitors and researchers have camped for the night.DADO GALDIERI/HILAEA MEDIA

A Juruna indigenous environmental monitor covers a turtle nest with sand

The Juruna people have been protecting and monitoring the population of the yellow-headed side-neck turtle (Podocnemis unifilis), which nests along the banks of the Xingu River.DADO GALDIERI/HILAEA MEDIA

A Juruna Indigenous monitor shows a turtle nest

An egg peeps from the nest of a yellow-headed side-neck turtle (Podocnemis unifilis).DADO GALDIERI/HILAEA MEDIA

The sacred Jericoa waterfalls

The Jericoá waterfalls in the Big Bend of the Xingu River are considered sacred to the Juruna people.DADO GALDIERI/HILAEA MEDIA

For the Juruna, no money or mitigation project can substitute for the altered pulse of the river and their own lives. “Belo Monte took our river, and it was like draining our blood out,” says Giliarde Juruna, Muratu’s chief. “Today, we are adapting to this new reality of drought. But we don’t know how our future will be without the river.”

The collaboration hopes its data can be used to push for more water to be released from the dam. In 2019, based on the Juruna’s data, IBAMA deemed the dam’s water flow insufficient and forced Norte Energia to temporarily increase it, reducing the amount of water delivered to the power turbines. IBAMA also asked the company to conduct further impact studies. In 2021, however, then-President Jair Bolsonaro’s administration reversed the ruling and allowed Norte Energia to reinstate the original, reduced water flux. The agency did require the company to invest 157 million reais ($29 million) in environmental and social mitigation actions, such as replanting trees.

In August 2022, the Juruna and their scientist partners sent IBAMA another proposed water regime that would increase the volume released from the dam by up to 68%. The increased flow would restore flooding to 32 mapped piracemas, or fish breeding sites, like those on the island of Zé Maria. The plan would also do away with the abrupt daily changes in flow that the river experiences now, like the one for which Norte Energia was fined in 2016. “The water needs to go up and down gradually to guarantee that the fish juveniles can develop,” says Janice Muriel Cunha, an ichthyologist at UFPA. “They need at least 3 months to grow in the calm waters of the flooded forests, and then go back to the main stream.”

Pablo and his cousin Thalisson release yellow-headed side-neck turtles

Pablo Juruna (right) and his cousin Thalisson Juruna release two yellow-headed side-neck turtles (Podocnemis unifilis) they found trapped in rocks on the banks of the Xingu River.DADO GALDIERI/HILAEA MEDIA

IBAMA is now evaluating the suggestion and should answer soon. But approval is unlikely, the researchers admit. More water down the river means less flowing to the turbines, and less electricity produced by a complex that is already falling short of expectations. Because of drought and poor planning, Belo Monte only generates on average 4571 megawatts of power, less than half its installed capacity. “Based on the history so far, it is difficult to believe that Norte Energia would reduce energy production to increase the water volume in the Big Bend,” Sawakuchi says.

THE JURUNA HOPE things will take a better turn with Lula. It’s unclear how the politician, who said in a recent interview that he would approve the construction of Belo Monte again, will follow through on his campaign promises on the environment. Biviany Rojas, who coordinates the program that supports the Juruna’s monitoring project at the Socio-Environmental Institute, expects that under the new government, IBAMA will recover the autonomy it had lost during Bolsonaro’s administration to make decisions based on technical information rather than on politics. “This is an opportunity for Lula to redeem himself with the Xingu people,” she says.

For his part, Josiel is confident there will be more dialogue between his people and the new government. But he remains concerned about the future, and not just for his people. There are about 150 other dams in the Amazon basin already, and 350 more are planned—including another on the Xingu, upstream from Belo Monte.

Although he only has a high school degree so far, Josiel has been thinking about becoming a biologist. The challenges to achieving that goal are multiple, but he thinks science can give a voice and memory to the knowledge of his people, passed down from generation to generation, including what he learned from his grandfather about the river and how to live from it. “It is a way to show future generations of our community how the river was before, how abundant the fish was,” he says. “And how it will never be again.”

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