China began building a massive dam on the Yarlung Tsangpo river near the disputed border with the northeastern Indian state of Arunachal Pradesh — which Beijing also claims — earlier this month at a ceremony attended by Chinese Premier Li Qiang.

It has sparked alarm in India given both the environmental risks and the potential leverage it offers China over water flow into northeast India and Bangladesh.

The estimated $170 billion (€147.4 billion) hydropower project aims to generate 300 billion kilowatt hours of electricity annually, supplying power primarily for transmission to other parts of China and meeting local demand in Tibet. It surpasses the giant Three Gorges Dam's capacity, currently the largest in the world.

Some experts and former diplomats believe the dam is likely to renew tensions between India and China, despite recent signs of a cautious improvement in ties, such as addressing border concerns.

Longstanding border dispute

The two nations have accused each other of trying to seize territory along their de facto border, known as the Line of Actual Control (LAC), which India claims is 3,488 kilometers (2,167 miles) long and China says is shorter.

After years of tension, both countries have renewed efforts to normalize relations.

In January, both sides agreed to resume flights after nearly five years. Three months later, India and China's special representatives decided to move forward by resuming pilgrimages and border trade.

However, the dam project introduces a major new fault line, as the ecological changes to the landscape are expected to trigger a range of geopolitical and environmental issues related to habitats and demography across the lower Himalayas.

India considers the Expert Level Mechanism (ELM) — a bilateral data-sharing framework — inadequate given the scale of dam project, as the ELM mainly provides information during the monsoon season, when flooding is a major risk.

"In the long run, as India argues, it will not only trap nutrient-rich sediments vital for downstream soil fertility in Assam and Bangladesh, thereby affecting irrigation," Aravind Yelery, associate professor at the Centre for East Asian Studies in Delhi's Jawaharlal Nehru University, told DW. The dam will "also impact crop yields and agricultural productivity, and compromise riverine ecosystems."

In Yelery's estimate, the transboundary rivers and China's approach to unilaterally altering the riverine ecosystem is disastrous environmentally and diplomatically.

Is there a risk of water exploitation?

"From a legal aspect, China is taking a felonious route to neglect its responsibility for preserving river flows due to geopolitical ambitions," said Yelery, adding that this has already had a profound impact on India's strategic approach to engaging in border talks.

China took a similar stance on the Mekong River, asserting upstream control while constructing several dams. Since the mid-1980s, China has built 11 large dams on the Mekong (Lancang), with more underway. 

"China has not entered into riparian agreement with any of its neighbors even though it controls the headworks of most major rivers in Asia," Atul Kumar, a China expert and fellow at the Observer Research Foundation, told DW.

"Beijing has adopted a similar stance in the Yarlung Tsangpo case and kept India and Bangladesh uninformed on these dam projects. Even the hydrological data sharing, a harmless technical detail, often depends on bilateral relationship and has often remained unavailable during tense periods," said Kumar.

A statement by Chinese Foreign Ministry spokesperson Guo Jiakun that the project "will not have any negative impact on the downstream regions" during a media briefing last week has been met with skepticism.

Arunachal Pradesh Chief Minister Pema Khandu described the Chinese mega dam project as a ticking "water bomb" and an existential threat that is a far bigger issue than the military threat.

'Downstream destruction'

"The issue is that China cannot be trusted. No one knows what they might do," Khandu told news agency PTI, stressing that China is not a signatory to the international water treaty that could have forced it to abide by global norms.

Kumar also raised concerns over the dam's risk of failure, which "would always remain a ticking bomb for downstream areas in northeast India and Bangladesh."

"In an unstable and earthquake-prone Himalayas, a natural disaster, conflict or even sabotage can bring destruction all over the downstream areas," said Kumar.

Former diplomat Anil Wadhwa called for a consultative mechanism and said China should disclose details about the dam's capacity, water flows and alignments, once construction has been completed.

"It is imperative that India takes all defensive measures in Arunachal Pradesh by constructing its own dam at the earliest" possibility, Wadhwa told DW.

"The local opposition should be compensated and open communication with the affected community will help lest the issue spiral as we have seen with other mega projects in the country."

That sentiment was echoed by former diplomat Ajay Bisaria, who told DW, "Given China's recent history of leveraging economic interdependence and trade as a geopolitical tool, India should assume China will weaponize the waters."

"While China's willingness to do so is evident, its capacity and the technical feasibility are yet to be seen. To mitigate that risk, India must proactively assess and game the worst-case scenario," Bisaria concluded.

Edited by: Keith Walker