This article was originally published on Mekong Eye.
CÁT BÀ, VIET NAM – You’re not supposed to see Cát Bà langurs. “If you see langurs, watch them quietly,” said Neahga Leonard, director of the Cát Bà Langur Conservation Project.
“You can’t go looking for them.”
These petite, orange-headed leaf-eaters – Trachypithecus poliocephalus – can only be seen on Cát Bà, the largest island in the UNESCO recognized Cát Bà Archipelago-Hạ Long Bay cluster.
Once hunted for traditional medicine, fewer than 100 survive in the wild, and their habitat is now under threat.
The noise-averse langurs avoid humans by retreating to high limestone caves and rocky cliffs – but even that’s no guarantee of peace, said Leonard. Tour guides, chasing rare sightings, take tourists deep into their habitat for picnics and loud karaoke sessions. One tour boat operator became so aggressive they rammed the project’s research boat and pushed it aside.
Cát Bà is a biodiverse haven made up of stunning karst towers, tropical forests, sandy beaches, emerald lakes, coastal mangroves and coral reefs. A total of 2,026 terrestrial and marine species, plus many unidentified flora and fauna, call the archipelago home. More than 12,000 residents’ livelihoods depend on the ecosystem, which is already strained by mass tourism.
The fragile ecosystem is now bracing for further disruptions as a 50-hectare land reclamation project is reshaping the island’s coastline – part of a grand plan to turn the island into a mega-entertainment hub.
The plan to fill in a section of Lan Hạ bay was launched in 2017, but nothing happened until the second half of 2024. Then, between August 2024 and March 2025, nearly 1.5 kilometers of coastline was filled in, Mekong Eye’s analysis of EU satellite imagery shows.
A total of 3.7 million tourists visited Cát Bà in 2024. With the new developments, the island expects to receive 4 million this year.
Developed by Vietnamese conglomerate Sun Group, the new landmass will host skyscrapers, luxury villas, hotels, clubs and one kilometer of artificial beach. The full vision for the entire island spans over 7,000 hectares, wrapping around Cát Bà National Park with a golf course, an entertainment complex and two resorts.
A cable car, the conglomerate’s signature infrastructure, is already in service – connecting Cát Bà with Hải Phòng, the country’s third largest metropolis.
Sun Group has promoted the project as Viet Nam’s first net-zero tourism development – but released no public environmental impact assessments or detailed carbon plan. It told state media it will ban single-use plastics, manage waste and wastewater with advanced systems and offer free cable car rides to residents who give up carbon-emitting personal vehicles.
As of April 2025, free electric shuttles were in service.
The conglomerate did not respond to Mekong Eye’s request for comment. WATG, one of the project’s listed urban planning consultants, declined to share details, citing a non-disclosure agreement with Sun Group.
Tiffany M Tran, a doctoral candidate at the University of Pennsylvania studying urbanization and coastal land reclamation in Indonesia and Viet Nam, warned that reclamation is a carbon-intensive process – from operating heavy machinery and managing waste to sand mining and the destruction of carbon-sequestering mangroves.
Emissions are often underestimated and hard to mitigate, research has shown.
“Conversion of water to land reduces the area of water to sequester [greenhouse gases], so that’s a reduction of carbon sinks,” she said. “For a reclamation project, if you think of carbon neutrality that’s something to include in your calculation.”
Yet emissions are only one part of the story. Tran said reclamation also disrupts fragile ecosystems on various scales and even poses risks to human health. Shrinking water bodies weaken their natural waste-flushing ability, she explained.
“Reducing the area of bays or estuaries can lower the tidal prism – the volume of water exchanged during tides. That weakens the system’s ability to flush out sediment and waste, leading to increased turbidity and pollution.”
Increased turbidity, or the cloudiness of water in bays and estuaries, can disturb marine life.
Filling in a bay can also alter wind dynamics and weaken waves, creating stagnant zones where waste accumulates, therefore harming coastal ecosystems and public health, Tran added.
Another major concern is the reduced oxygen exchange between the ocean and the air, which lowers oxygen levels in the water – threatening marine species like fish.
Reclaimed land is also more prone to sinking, making the filled area more prone to flooding and sea level rise, she warned.
Though land reclamation has existed for millennia, Tran said developers must tread carefully when planning large-scale projects. Bays, estuaries and shallow water are not empty spaces to be developed, but vital habitats that filter waste and serve as the “kidneys of the Earth”, she said.
“Disabling the Earth’s kidneys is something we have to think carefully about,” Tran added.
Noise, dust and barriers
Before the ecosystem bears the brunt of these changes, seafront hotel owners and tour guides say they are already feeling the impact on their livelihoods.
When reporters visited the reclamation site in February 2025, views of Cát Bà’s iconic karst towers and emerald waters were interrupted by vast stretches of sand with the sound of heavy machinery in the background. The bayside walkway was blocked by tubes dumping water and uprooting pathway tiles.
Locals said tourist numbers were unusually low for the island’s off-season.
“Since this project started, it’s been full of noise and air pollution,” said Đoàn Cường, a tour guide speaking under a pseudonym. “Many hotels lost their sea view.”
Fishers, already struggling with declining fish stocks, now face new restrictions. In Cái Bèo, a fish seller speaking under pseudonym Bích, said the local government now limits fishing and aquaculture to long-term residents. Married to a Cát Bà native, she was allowed to stay – but hundreds of others were told to leave.
“Before, we had 300 to 400 fishing rafts. Now, it’s just over 100,” she said. “Many are just anchored. They are not allowed to raise fish anymore.”
While most families claimed the project has not directly affected them, others like Tùng, also speaking under a pseudonym, was frustrated by the sudden restrictions implemented last year and felt he was not properly informed.
“They don’t allow us to fish nearby the sand-dumping zone anymore,” he lamented. “If you get too close, they chase you away.”
Tùng admits he is frightened at the project’s scale.
“They’re cutting into mountains and filling up the sea. I can’t believe they’re actually able to fill in the ocean like that,” he said.
A looming spillover
Cường, the Cát Bà tour guide, remained hopeful that more tourists would return for the island’s natural beauty once the project was finished. He believed Cát Bà would not follow the path of the southern island of Phú Quốc – where unchecked development drove tourists away – because much of this island is under protected status.
Yet conservation groups say protection on paper does not guarantee a rosy picture on the ground. It may even put the wider Hạ Long Bay ecosystem at risk.
The Vietnamese government spent more than a decade lobbying to include the Cát Bà archipelago in Hạ Long Bay’s UNESCO Natural World Heritage designation. Though successful in 2023, the extension faced strong opposition and went against advice from conservation groups, according to UNESCO documents.
Only months before the designation, the International Union for Conservation of Nature (IUCN) advised against it, citing environmental risks from increasing port and fishing activities and tourism within and near the protected site.
When asked to evaluate the site again in 2023, IUCN doubled down. It warned that protected status had failed to shield Hạ Long Bay from overtourism, vessel pollution and waste – and that adding Cát Bà, with its weak zoning and limited buffer zones between tourism and conservation areas, would only worsen things.
The IUCN did not mention Sun Group’s project, which was only in the planning phase at the time, but it flagged similar threats. The organization’s report cited Vinaconex’s 1.72 square kilometer Amantina resort west of the Sun site as an example of large developments likely to “cause further fragmentation and demands for natural resources.”
“IUCN considers that the integrity of HLB and CBA is currently under serious threat,” the report stated. “In addition, IUCN notes with concern that the prospect of further large-scale tourism development will likely compromise the integrity of the proposed extension [sic] further.”
Beyond one species
Cát Bà langurs have likely been endangered for centuries, perhaps as far back as 1,500 years, said Leonard. His team keeps a census of the langurs, but avoids fixating on the count. What matters more, he said, is preserving their critical habitat – the karst mountains.
Langurs are considered an “umbrella species” for their cute appearance, which draws attention from global tourists, and for their endemic status, which evokes pride among Vietnamese.
Conservationists use this appeal to promote broader ecosystem awareness – from rare snails to plants that thrive within the vast limestone landscape.
“The umbrella species concept is useful,” Leonard said. “It is a bit frustrating, because so many species are left out, but we can use it to say this allows us to protect the habitat they all live in.”
Although Sun Group’s rapid development is technically outside Cát Bà National Park, Leonard warned there will be fallout for the karst ecosystem that could impact langurs. He also noted the absence of consistent marine protection around Cát Bà, unlike the focused inland conservation efforts.
“We keep seeing really heavy impacts and very little long-term planning,” he said. “[It’s] about who can come in and make the most money the fastest.”
“They are not thinking about why people come to these places,” he added.
Leonard said he had never been approached by Sun Group, and his outreach efforts were ignored, despite a strong working relationship with the Hải Phòng government. Still, he hopes developers will eventually see conservationists as allies, not obstacles.
“Conservation organizations and conservation in general is [sic] absolutely not against development and tourism, but for those things to be effective, there has to be communication between all the different interested parties, especially professionals in ecology, so that a good long-term plan can be made.”