Hundreds of miles from China’s populous coastline, a sharp bend in a remote Himalayan river is set to become the centerpiece of one of the country’s most ambitious – and controversial – infrastructure projects to date.
There, a $168 billion hydropower system is expected to generate more electricity than any other in the world – a vast boon for China as it hurtles toward a future where electric vehicles dominate its highways and power-hungry AI models race to out-compute international rivals.
Chinese leader Xi Jinping called for the project to be “advanced forcefully, systematically, and effectively” during a rare visit earlier this year to Tibet, a region where Beijing continues to tighten its grip in the name of economic growth and stability.
Experts say the hydropower system, built in the lower reaches of Tibet’s Yarlung Tsangpo river, will be a feat of engineering unlike any ever undertaken. Leveraging a 2,000-meter altitude drop by blasting tunnels through a mountain, it will enable China to harness a major river in a region known as Asia’s water tower and at a time when governments are sharpening their focus on water security.
The project could aid global efforts to slow climate change, by helping China – now the world’s largest carbon emitter – wean off coal-powered energy. But its construction could also disrupt a rare, pristine ecosystem and the ancestral homes of indigenous residents.
Tens of millions of people also depend on the river downstream in India and Bangladesh, where experts say the potential impact on the ecosystem, including on fishing and farming, remain understudied.
Headlines in India have already dubbed the project a potential “water bomb” – and its proximity to the disputed China-India border put it at risk of becoming a flashpoint in a long-simmering territorial dispute between the two nuclear-armed powers.
Despite these stakes, the project remains shrouded in secrecy, deepening questions about a plan that shows China’s immense technical capabilities and drive for clean energy, but also its lack of transparency, even when it comes to an undertaking with potentially far-reaching consequences.
Clues about the project’s design – both referenced in official or scientific reports and from open-source information compiled by CNN – suggest a complex system that could include dams and reservoirs along the Yarlung Tsangpo river, as well as a series of underground hydropower stations connected by tunnels, harnessing energy as a diverted portion of the river makes a steep elevation decline.
“This is the most sophisticated, innovative dam system the planet has ever seen,” said Brian Eyler, director of the Energy, Water, and Sustainability Program at the Stimson Center think tank in Washington. “It’s also the riskiest and potentially the most dangerous.”
China disagrees. In a statement to CNN, its Ministry of Foreign Affairs said that the project had “undergone decades of in-depth research” and “implemented thorough measures for engineering safety and ecological protection to ensure it will not adversely affect downstream areas.”
“Since the initial preparation and official commencement of the project, the Chinese side has always maintained transparency regarding pertinent information and has kept open lines of communication with downstream countries,” the ministry said, adding that “as the project progresses” Beijing would “share necessary information with the international community” and “strengthen communication and cooperation with downstream countries.”
The project, it said, “aims to accelerate the development of clean energy, improve local livelihoods, and actively address climate change.”
But Beijing may have other priorities in mind, too. The ambitious infrastructure move comes as Xi pushes to shore up national security not just by ensuring China’s energy supply – but also tightening control along disputed borders and regions home to ethnic minorities.
“If you connect the dots of Chinese infrastructure development in the Himalayas, especially in areas where China borders India along Tibet, they are strategically placed,” said Rishi Gupta, assistant director at the Asia Society Policy Institute in New Delhi.
“The project aligns with China’s broader goal of leveraging its natural resources to consolidate control over critical regions like Tibet and its borders.”
Known as the world’s highest major river, the Yarlung Tsangpo winds its way from a glacier in the Himalayas across the plateau that cradled Tibetan Buddhism, and toward the country’s southernmost edge.
One stretch of the river, tucked alongside Tibet’s de facto border with an Indian state whose land China claims, has long drawn attention for its power-generating potential.
There, the waterway makes a dramatic horseshoe turn as it wraps around a mass of mountains at what’s known as the Great Bend – a trajectory that sees the river lose some 2,000 meters in altitude within roughly 50 kilometers.
That descent has been estimated to have the potential to generate some 300 billion kilowatt-hours of electricity annually – roughly triple the output of China’s Three Gorges Dam, currently the world’s most powerful.
The hydropower development on the lower Yarlung Tsangpo “isn’t merely a hydropower initiative,” it is also a national security project, encompassing water resource security, territorial security, and more, Yan Zhiyong, then chairman of the Power Construction Corporation of China (PowerChina), said in a 2020 speech, according to Chinese state media publication.
Such a project along the river’s lower reaches has been talked about for decades but never attempted – long seen as a notoriously challenging undertaking in a remote and treacherous area, difficult even for a country that leads the world in building mega-dams.
Now, satellite images, publicly available corporate documents, and social media posts from the area reviewed by CNN show work is underway building and widening roads, constructing bridges, erecting storage facilities for explosives, expanding cell service and relocating villagers – all apparent efforts to make way for construction, which officially began in July.
Official documents often refer to the project using the Roman initials “YX” to denote an abbreviation for the lower reaches of the Yarlung Tsangpo, but they provide limited information about its design. State media has said the project primarily employs a method of “straightening and diverting the river” through tunnels and includes five cascade hydropower stations.
CNN’s examination of open-source information, including academic research papers, official tenders, patents for power station designs filed by a subsidiary of PowerChina, a local town planning document, as well as satellite imagery and social media posts from the area has shed more light on how this expansive project may be taking shape.
A simulation based off this information and produced in conjunction with experts at the Stimson Center’s Energy, Water, and Sustainability Program, who provided technical and geographic analysis, suggest the design could be a sprawling system of hydropower stations, tunnels and reservoirs, which together could span some 150 kilometers as the crow flies from the first to the final power station.
That system would begin with a reservoir created by a dam at Mainling city, where Chinese Premier Li Qiang attended a groundbreaking ceremony for the project in July. The reservoir there – which could stretch dozens of miles according to the simulation – would enable operators to regulate the water flow throughout the hydropower system.
A second, lower dam, located further downstream and past a protected national wetland, would likely be used to divert a portion of the river away from the Great Bend and into a system of tunnels blasted through mountains and beneath an adjacent valley, according to the simulation of the potential design.
Here, the diverted water would likely pass through a series of cascade power stations, each hundreds of meters lower in elevation than the last – generating immense power along the way before rejoining the main river once again.
The exact locations of all five stations are unknown, as is how much land will be inundated by reservoirs to create this system.
Another key question for such a design is whether the system will have a final dam and power station that will allow operators to control the overall flow of the main river before it traverses countries downstream.
Experts say that a final dam, which could include a power station and be located closer to the de facto border with India, would be an optional addition to the main project because of the cost, challenges and potential risk.
A paper by Chinese government scientists published in the Nature journal Communications Earth & Environment earlier this year appeared to confirm that two reservoirs upstream of the diversion tunnels will regulate how much water goes into those tunnels, while a third, downstream, will regulate the water as it flows back into the main river. But experts stress that until China releases more details, independent efforts to assess the project can only be based on best guesses.
“With what we know it is nearly impossible to understand (or) evaluate the possible impacts that the project will have,” said Rafael Jan Pablo Schmitt, a hydropower expert at the University of California–Santa Barbara, who discussed the simulation with CNN and the Stimson Center.
What is clear is that to build the hydropower system, Chinese engineers and hydrologists will need to operate in notoriously challenging conditions. The river runs through one of the world’s most seismically active regions, where even the mountains themselves are continuing to grow by millimeters each year – risking disruption to carefully calibrated engineering.
“The challenge will be to build a system that can mitigate or avoid safety risk,” said Eyler. “The system is very complicated. There’s a lot of concrete poured for multiple dams and tunnels cutting through seismically active mountains. China prioritizes dam safety … but can you mitigate risk in the Himalayas?”
Landslides, debris flows and glacial lake outburst floods are all features of the area that are becoming more unpredictable with climate change and have the potential to damage infrastructure and put people downstream at risk if the project can’t cope.
Experts say Chinese engineers are among the best in the world and will have designed mitigation efforts for earthquakes and other hazards – but those will be untested in such an environment.
“It’s just staggering that (Chinese officials) would commit to building this that far out in such a challenging geopolitical and geotechnical environment,” said Darrin Magee, a scholar of Chinese hydropower at Western Washington University in the US. “If China’s leadership is now convinced that it can go toe to toe with the world’s leading AI developers … it’s nice to have a basically unlimited source of electricity in your back pocket,” he added.
And as Beijing looks to swap imported petroleum for home-grown electricity, “they’re betting on a payoff that’s going to last decades,” Magee said.
China has a history of building complex and controversial dams.
The Three Gorges project – a dam rising nearly half the height of the Empire State Building – required uprooting more than a million people before it began operation in 2003, and has had a mixed record on flood control, despite promises that it would serve this purpose.
Today, China’s rivers are dotted with hydropower projects, while cutting-edge transmission lines carry high-voltage electricity from rural and mountainous regions to the skyscrapers, AC units and electric vehicles of urban China.
Nearly a third of the total installed capacity of hydropower globally as of 2024 was in China, and the country is on track to meet targets for new capacity early – part of Xi’s push to electrify China as he aims for ambitious climate goals and energy security.
In Tibet, Chinese authorities aim to transform the region into a green energy hub. In that vision, hydropower is linked to sprawling installations of solar and wind farms that are used to power a high-altitude supercomputing industry and send electricity eastward, while “boosting local people’s livelihood and prosperity.”
But this plan also places the infrastructure needed for China’s technological and energy transition in the heart of an ecologically sensitive region.
At the Great Bend, the Yarlung Tsangpo is bound on two sides by the world’s deepest canyon, cut into a landscape of pristine forest flanked by mountains and designated one of China’s national-level nature reserves.
There, towering cypress trees have grown for hundreds of years and vulnerable or endangered species like Bengal tigers, clouded leopards, black bears, and red pandas live in habitats that morph with the rising geography – and new plant and animal species continue to be discovered.
“The Great Bend of the Yarlung Tsangpo is one of the most extraordinary geological and ecological phenomena on the planet,” said Ruth Gamble, an environmental, cultural and climate historian of Tibet at La Trobe University in Australia. “Within a couple of hundred kilometers you go from peaks of nearly 8,000 meters to tropical jungles.”
For years, scientists and rights groups have raised concerns about infrastructure development in this area.
In a paper published last year, scientists from Peking University in Beijing called for extensive biodiversity surveys to be “urgently conducted before the dam project commences” so that the “value of local nature is sufficiently identified and the dam’s environmental impacts can be accurately assessed.” The corresponding authors did not respond to a CNN request for comment.
German-based rights group the Society for Threatened Peoples earlier this year sent a letter to the United Nations Human Rights Council accusing China of violating its own regulations that restrict placing production facilities in core or buffer zones of nature reserves.
Beijing earlier this year said the project “strictly adhered” to an ecological protection law and included an “advanced environmental monitoring system” to prevent impacts on “key ecological zones and the habitats of rare wildlife.”
A company notice reviewed by CNN showed that a state-owned entity involved with constructing the project was seeking technical consulting services to assess biodiversity impacts. The notice, dated October last year, wrote that such an assessment was a “prerequisite” for obtaining a construction permit as the hydropower base “cannot avoid the nature reserve” area of the canyon. The results of an assessment do not appear to have been made public.
During his visit to Tibet in July, Premier Li exhorted those involved in the project to “ensure that the ecological environment is not damaged.” But experts question how infrastructure of this scale could not have an impact.
“Rivers don’t stop at national park borders, and neither do snow leopards or other types of animals, or even plants and trees,” said Gamble.
Another looming question is how deeply the project will disrupt the region’s people, some of whom have lived for generations in a corner of the country largely untouched by China’s infrastructure ambitions.
Several tens of thousands of people live in the counties where the projects will be built, among them indigenous groups including the Monpa and Lhoba people, two of the country’s smallest officially recognized ethnic minorities.
Chinese officials have acknowledged the project will require “relocating local communities” in Tibet and said “new places of worship” had been located near “newly built residential areas” – a sign of the disruption to daily and cultural life associated with the project.
Local officials have reported verifying household registrations for the eventual village relocation and say they are scrambling to document what they described on social media as a surge of migrant workers attracted by the project.
Governments in Mainling city and Medog county, where the downstream section of the project is being built, both issued warnings to “crack down harshly” on any crimes that could disrupt a “major national construction project.”
In Medog county, videos posted by social media users show long lines of cars and trucks flying Chinese flags and propaganda banners, transporting villagers from their hometown to new abodes closer to the de facto China-India border.
“Moving takes people and belongings, but the memories stay behind,” one woman who said she was being relocated wrote on social media. “Arriving at the new location, I feel a mix of emotions, unsure when I’ll be able to visit my hometown again,” she said.
It’s unclear if these residents’ homes will be directly impacted by dam construction, but that social media user wrote they were moving due to the “hydropower project.” Beijing has also in recent years presided over a policy of relocating villages to fortify or in some cases expand its claim along disputed boundaries.
China’s Foreign Ministry earlier this year said Beijing’s resettlement plan for the project would “prioritize the rights, participation, and well-being of affected residents” and “respect local religious beliefs and cultural heritage by strategically avoiding religious sites.” State news agency Xinhua has said the project would help the economy and “create new jobs,” thus “enhancing the sense of gain, happiness and security for people of all ethnic groups.”
But the risks from hydropower projects on the local communities “are immense,” according to Tempa Gyaltsen Zamlha, deputy director of the Tibet Policy Institute in Dharamsala, the town in India where the Dalai Lama, the exiled Tibetan spiritual leader, and his loyalists reside.
“People could face forced displacement from their ancestral homes … destruction to the source of local income, destruction of local ecological balance and wildlife habitat, influx of migrant workers from China replacing the local population in the region,” he said.
Concerns about the project are also being acutely felt downstream in India, where the Yarlung Tsangpo becomes known as the Brahmaputra – a mighty waterway that supports fishing and farming in India and Bangladesh before ultimately emptying into the Bay of Bengal.
The top official in India’s Arunachal Pradesh, just over the de facto border from Tibet, warned in July that the dam posed an existential threat to the people of the region and could be used as a “water bomb” by China.
“China cannot be trusted. No one knows what they will do and when,” Chief Minister Pema Khandu said in an interview with the Press Trust of India, pointing to how releasing or withholding water could overwhelm or dry out his region.
In New Delhi, officials earlier this year said they were “carefully monitoring” China’s hydropower plans and vowed “necessary measures to protect our interests, including preventive and corrective measures to safeguard life and livelihood of Indian citizens.” CNN has reached out to India’s Ministry of External Affairs for comment on the project and China’s information and data sharing around it.
The situation also threatens to upset a complicated diplomatic balance between China and India as they try to ease tensions along their heavily militarized border. During a meeting in New Delhi in August, top officials from both sides discussed “trans-border rivers cooperation,” and China agreed to share hydrological data “during emergency situations,” according to an Indian government readout.
China already has a controversial track record of running dams along another transnational river, the Mekong. Its operators there have been accused of causing drought in Vietnam by using reservoirs and dams to manipulate the river to maximize power-generation – a claim Beijing denies.
For the YX project, Chinese researchers and officials have played up its potential to mitigate flood risk, saying it could help safeguard downstream regions as flooding becomes more uncertain due to climate change.
Experts agree an upstream dam could have a positive impact on flooding – a major issue in both India and Bangladesh, where extreme floods during monsoon seasons take lives and devastate crops and homes across the countries’ densely populated floodplains – but say it’s impossible to know without more information.
“While the dam could potentially regulate monsoon floods, mismanagement – such as sudden water releases – might intensify flood risks,” said water governance expert Anamika Barua, a professor at the Indian Institute of Technology Guwahati in Assam, another Indian region traversed by the river. “Transparent data sharing and cooperative management will be critical to reducing disputes.”
And while the Brahmaputra draws most of its waters from tributaries and monsoon rains rather than the Yarlung Tsangpo, changes in the waterflow upstream could disrupt the natural pulse of the river and the kind of sediment and fish it carries – key elements for the river and delta ecosystems downstream.
For those living just over the de facto border, the vast unknowns about China’s project are already having an impact.
There, officials from India’s largest state-backed hydropower firm are pushing forward their own project – a 11,200 megawatt dam on the same river – spurred by the hydropower development upstream.
That project would require relocating villages home to indigenous groups that rely on farming for subsistence – and has sparked local opposition and concern, according to people familiar with the situation.
“They keep saying ‘China this’ and ‘China that,’ but we don’t even know what China is building,” Tagori Mize, a spokesperson for a local indigenous farmers group told CNN. “We are not even being told where we will live. Nothing is clear.”
With both countries preparing their projects, experts like Stimson’s Eyler see another outcome from China’s push: a dam-building race.
“If the two countries could work together on the overall design of the mega-dam system, then some risk could be avoided,” he said. But otherwise, for the river, “a dam building race between India and China is a race to the bottom.”
EDITOR’S NOTE: How we created our simulation of the hydropower system
CNN and experts from the Stimson Center’s Energy, Water, and Sustainability Program in Washington created a simulation of one possible design for the hydropower project on the lower reaches of the Yarlung Tsangpo. The simulation was created using official statements and open-source information including satellite imagery, social media posts, research papers, official company and local government documents, as well analysis of the surrounding geography and technical assessments by the Stimson Center, with feedback from outside experts. There are different levels of confidence for different aspects of the design.
Determining the location of the Mainling dam:
CNN reviewed and geolocated social media posts from Tibet suggesting locations for dam site surveys, as well as satellite imagery showing suspected new company buildings and factories.
A tender from a state-owned company involved in the project provided a detailed description of the Mainling dam site. CNN geolocated it near Tashi Rabten town, matching the location indicated by the social media posts and satellite images.
Based on this information, CNN concluded the first dam would be at the valley near Tashi Rabten town and shared it with Stimson Center. Later, Chinese Premier Li Qiang in July attended a groundbreaking ceremony for the YX project at a dam site in Mainling, according to Chinese state media. CNN geolocated the site of the ceremony, which confirmed its earlier findings.
Projecting the location of a second dam at Pei Town:
CNN reviewed social media posts from the area and satellite imagery to determine an estimated location for the portion of the project that will divert the river through the mountain.
Several signs indicated a location near Pei town, including a plaque at Datogka village, dating back to the early 2000s, which said it would be the site of a future Yarlung Tsangpo dam.
Social media posts report construction worker dormitories for the dam project at Yusong village, downstream of Pei town and Datogka village.
A local government planning document reviewed by CNN confirms that one of the Pei town goals is to build the town as a “key national hydropower energy hub” and includes a map showing the majority of the current town will be kept intact, which suggests a small portion will be inundated, indicating the water level of the Pei town reservoir will be very low.
Chinese leader Xi Jinping and Premier Li Qiang to Tibet visited Yani Wetland on trips to Tibet in recent years, and both emphasized the importance of ecological preservation, suggesting that the wetland will be preserved at least in part.
Projecting the location of tunnels and hydropower stations:
CNN reviewed publicly available patents that appeared to have been filed during the design of the project and an official tender, both from a state-owned company involved in the YX project, as well as a 2023 academic study, to make estimations about the location of the tunnel system and the hydropower stations within it.
Satellite and social media imagery also show the widening and closure to public use of a highway from Pei town area to Medog county, suggesting it could be used to support tunnel construction nearby.
The exact locations of all five cascade hydropower stations remain unknown. However, the CNN/Stimson team believes some will be inside the tunnel system and there could be a roughly 700-meter drop in elevation between each of those power stations, with a total of three power stations built under the mountains and an adjacent valley. Together with a power station at the Mainling dam and a projected one further downstream, there would be a total of five power stations, matching the official disclosure.
A major state-owned company and subsidiary of PowerChina involved with the project published a tender in May 2024 noting the general locations of its five bases. This information, taken alongside a review of designs for patents from the same company and a technical assessment, suggest potential locations for two of the power stations within the tunnel system. A third also in that system could be located closer to the main river to allow for water discharge there.
Experts have also suggested the Jinping II hydropower system in Sichuan could be a test model for the YX project. That system also features a structure with a low dam and a single hydropower station at the outlet of a tunnel redirecting water.
Considering the final hydropower station and a potential dam:
There is less publicly available information available about the location of the fifth hydropower station, as well as regarding whether there would be a final dam in the system.
A paper from Chinese scientists published in the Nature journal Communications Earth & Environment said there would be a third reservoir that “redirects water back to the natural river” downstream of the tunnel system.
Experts interviewed by CNN suggest that a final dam on the main river could be unnecessary to the design and create additional engineering challenges, though it would enable the downstream flow of water to be better regulated.
Some evidence, including social media discussion, satellite imagery showing large-scale construction, road-widening projects, entry restrictions suggest one possible location would be a dam near Xirang village, not far from the de facto border with India.
