China’s has announced a new mega hydropower project on its Yarlung Zangbo River. This will be the largest dam in the world. The estimated cost is whopping US$ 170 billion.  This has stirred waves of concern far beyond its borders. While Beijing touts the dam as a “project of the century,” promising renewable energy, regional economic growth, and a greener footprint, the reality is far more troubling. Beyond China’s borders, the cascading effects of such an enormous project threaten to destabilize fragile ecosystems, deepen regional water insecurity, and increase tensions with neighboring countries, particularly Nepal, Bhutan, and Bangladesh, all of which rely heavily on the river systems that originate on the Tibetan Plateau.

The Yarlung Zangbo River, which plunges dramatically through the world’s deepest gorge before flowing into India and eventually Bangladesh as the Brahmaputra, is more than just a natural wonder; it is the lifeline for millions downstream. Bangladesh, sitting at the delta of this river system, is perhaps the most vulnerable. Already one of the most climate-exposed countries in the world, Bangladesh depends on consistent river flows for agriculture, fisheries, and drinking water. Large-scale upstream damming threatens to reduce water availability during critical growing seasons, jeopardizing food security for a population of over 170 million. The country’s fertile floodplains are already under pressure from rising sea levels and saline intrusion; any disruption in the river’s natural flow could exacerbate these problems and lead to catastrophic outcomes for livelihoods and urban water supply. Moreover, Bangladesh’s energy security strategy, which depends partly on transboundary water cooperation with India, risks further destabilization if China unilaterally alters river flow upstream.

Bhutan, though less frequently mentioned, also faces grave risks. The Himalayan nation, which has built its own hydropower-driven economy in collaboration with India, relies on the predictable seasonal flow of rivers originating in Tibet. A massive diversion or alteration caused by China’s dam could change downstream water volume and sediment flow, thereby destabilizing Bhutan’s own hydropower projects. For a nation where hydropower makes up around 30 percent of GDP and over 70 percent of export revenue, such upstream disruption could spell both economic and social crisis. Bhutan’s fragile mountain ecosystems are also particularly vulnerable to seismic disturbances, and the new dam is being constructed in a zone known for high tectonic activity. The risk of earthquakes or landslides triggering dam collapse would be devastating not only for Tibet but also for Bhutan’s delicate river valleys.

Nepal, too, is caught in this unfolding drama. While the country has long hoped to harness its rivers for sustainable development, Chinese projects upstream threaten to undercut those ambitions. Reduced water flow and altered river dynamics would weaken Nepal’s own capacity to generate hydroelectricity, even as it struggles with chronic electricity shortages. Furthermore, Nepal’s agriculture, which employs more than 60 percent of its workforce, depends heavily on glacial melt and river irrigation. A sharp decline in downstream water availability, or sudden glacial lake outburst floods triggered by upstream dam construction, could devastate crops and rural economies. Beyond the economic toll, Nepal also faces the uncomfortable geopolitical reality of being squeezed between two hydropower giants, India and China, each seeking to dominate the regional water narrative.

Critics argue that China’s dam construction represents not merely an energy project but a strategic instrument of regional influence. By controlling the headwaters of rivers that sustain South Asia, Beijing gains leverage over smaller, downstream states. This hydro political dominance is particularly alarming because it comes in the absence of robust transboundary water treaties. Unlike the Indus Water Treaty between India and Pakistan, or the Ganges Water Sharing Agreement between India and Bangladesh, no binding framework governs China’s use of rivers originating in Tibet. Instead, Beijing has pursued a pattern of unilateral action: constructing dams first and discussing implications later. For neighbours like Nepal, Bhutan, and Bangladesh, this lack of transparency leaves them dangerously exposed to the whims of Chinese policymakers.

Environmental consequences are equally alarming. The Tibetan Plateau, often referred to as the “Third Pole” because it contains the largest reserves of freshwater outside the Arctic and Antarctic, sustains not only South Asia but also Southeast Asia. Rivers originating here feed nearly two billion people. Large-scale damming disrupts sediment flow, which in turn diminishes soil fertility in floodplains downstream. Bangladesh’s famed fertility, which supports its role as one of the world’s top rice producers, is heavily dependent on this natural replenishment of nutrients. Alterations to the river system will accelerate soil degradation, increase dependence on chemical fertilizers, and harm biodiversity in one of the most ecologically rich regions of the world.

China has tried its best to downplay these problems to neighbouring countries. It claims that the Yarlung Zangbo dam will not have drastic effect downstream but past precedents prove otherwise.On the Mekong River, where China has already constructed 11 dams, downstream countries like Laos, Cambodia, Thailand, and Vietnam have experienced unprecedented drops in river levels, fisheries collapse, and agricultural distress. These impacts, well-documented by independent researchers and the Mekong River Commission, serve as a chilling warning of what could await South Asia’s river basins. For Bangladesh, which is far more low-lying and climate-stressed than Mekong delta nations, the consequences could be catastrophic.

In addition to environmental and economic risks, the dam raises profound security concerns. In the event of geopolitical tensions, China’s control over critical upstream infrastructure could give it coercive leverage over neighbours. A controlled release of water, or worse, the threat of deliberate flooding, could be used as a strategic weapon. This is not mere speculation; in 2000, China’s sudden release of water from a dam on the Yarlung Zangbo caused flash floods in Arunachal Pradesh, killing at least 30 people. The event highlighted the lack of warning mechanisms and underscored the danger of weaponizing water in a geopolitically tense region.

Ultimately, China’s pursuit of the world’s largest dam is less a triumph of renewable energy than a troubling symbol of unchecked ambition. By prioritizing domestic economic stimulus over ecological balance and regional cooperation, Beijing risks destabilizing the livelihoods of millions in neighbouring states. Nepal, Bhutan, and Bangladesh—already grappling with climate vulnerability, economic fragility, and limited geopolitical clout—stand to pay the highest price. Unless there is greater international scrutiny, transparent governance, and a binding water-sharing framework, the Yarlung Zangbo project may one day be remembered not as a “project of the century,” but as the beginning of a century-long ecological and geopolitical crisis in South Asia.