The sprawling Sundarbans, home of the Bengal tiger and pristine mangroves, could become a toxic dumping ground if a massive coal plant is built near its borders, a United Nations agency warned this week.

The 1,320-megawatt Rampal plant under construction in Bangladesh would "irreversibly damage" the World Heritage Site if built as planned, UNESCO's World Heritage Center said Tuesday in a joint report with the International Union for Conservation of Nature (IUCN).

The two organizations formally recommended that Rampal's developers cancel the project and move it to a safer location.

They also recommended that Bangladesh halt development of the Orion Khulna coal plant, a 660-megawatt facility in the vicinity of the Sundarbans.

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The U.N.-backed report is the result of a months-long research mission to determine how the coal projects and other developments would affect the World Heritage site. It also comes as major environmental groups such as Sierra Club and 350.org are lobbying to scrap the plants.

"There is a very substantial threat of air pollution and water pollution," Fanny Douvere, who coordinates the World Heritage Center's marine program, told Mashable.

"A lot of the things that are being proposed for Rampal would not be permitted elsewhere where there are higher [environmental] standards," she said by phone from Paris.

The Sundarbans lie on the delta of the Ganges, Brahmaputra and Meghna rivers.Credit: IUCN/Mizuki Murai

Rampal is being built just 14 kilometers, or 8.7 miles, from the boundary of the Sundarbans, the world's largest mangrove forest.

Spanning 140,000 hectares in Bangladesh and India on the Bay of Bengal, the Sundarbans are home to critically endangered species such as the Royal Bengal Tiger, the Ganges and Irrawaddy river dolphins, and estuarine crocodiles.

The Sundarbans were deemed a World Heritage site in 1987 for their 'outstanding universal value,' meaning the forest is one of the most remarkable places in nature.

The coal plant's developer, Bangladesh-India Friendship Power Co. Ltd., is a joint venture between major power companies in both nations. The governments of India and Bangladesh, which are heavily subsidizing the $1.82 billion coal plant, insist the project is safe.

Tawfiq-e-Elahi Chowdury, a top energy adviser in Bangladesh, said Rampal would have no adverse impact on the Sundarbans, Bangladeshi media reported in July.

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Map of Sundarbans National Park in Bangladesh.Credit: Wikicommons

Douvere said she and her partners at IUCN met with the plant's developers and government officials during a fact-finding mission to Bangladesh in March.

The team ultimately found the coal plant would pose at least four substantial threats to the area.

The first and second threats include air and water pollution from dirty smokestacks, windblown coal ash and power plant wastewater and waste ash that could blow or leak into the nearby Sundarbans.

Third, building and operating the plant will require significant dredging and shipping that could destroy dolphin habitats and biodiversity. It may also strain the forest's freshwater flow, which is drastically declining as rising sea levels, port developments and increased shipping activities cause saltwater intrusion.

The fourth threat is the cumulative impact of all the industrial and related development infrastructure, such as barges to move the coal and facilities to store it, plus transmission lines to carry the plant's electricity to cities.

The World Heritage site is not permanently inhabited, but an estimated 6.5 million people depend directly or indirectly on the wider Sundarbans ecosystem.Credit: IUCN/Mizuki Murai

On top of this, the government's Environmental Impact Assessment of Rampal fails to identify the measures or procedures needed to avoid these impacts, said Remco Van Merm, the conservation officer at IUCN's World Heritage program.

The assessment "further reinforces IUCN's conclusion that this development is likely to have a negative impact on the environment," he told Mashableby email.

Destroying parts of the Sundarbans could eventually cause the local extinction of several endangered species, Van Merm added. It may also make local communities more vulnerable to storms, floods and cyclones as the protective forest buffer disappears.

"Only intact healthy ecosystems can continue to efficiently provide these services," he said.

The Rampal coal plant isn't just a threat to the environment: It also poses a large financial risk, the Institute for Energy Economics and Financial Analysis, a Cleveland-based research group, said in a June report.

The institute said electricity rates in Bangladesh are expected to rise to help offset the costs of the plant. At the same time, energy demand isn't likely to be high enough to keep the plant running at full capacity, meaning the plant could earn less money than expected.

Rampal coal power plant site; Wikimapia image accessed May 2016.Credit: Sourcewatch

"The proposed Rampal power plant is fraught with unacceptable risk, out of step with the times, and would set Bangladesh back," the institute said in its report.

Rampal's sole debt backer is the Export-Import Bank of India, which has committed a $1.6 billion loan to build the plant, according to BankTrack, a global network of non-governmental organizations that tracks the private financial sector.

Other financial backers are indirectly involved in the coal plant as shareholders, bondholders or underwriters through NTPC, India's largest power utility, or the import-export bank , Yann Louvel, BankTrack's climate and energy campaign coordinator, told Mashable.

Douvere of the World Heritage Center noted that Tuesday's report is not a blanket recommendation against all coal plants in Bangladesh.

"We're not saying the country shouldn't have any coal power plants," she said. "But it's very much a problem when it is going to jeopardize the 'outstanding universal value' of a place."