China has broken ground on what it says will be the world’s largest hydropower project, a $170 billion feat capable of generating enough electricity each year to power Britain. The scheme dwarfs the mighty Three Gorges Dam, currently the world’s largest, and Chinese construction and engineering stocks surged after Premier Li Qiang unveiled it on the weekend. For Beijing, the project promises clean power, jobs and a jolt of stimulus for a slowing economy. For neighbours downstream, it stirs old anxieties about water security: the Yarlung Zangbo becomes the Brahmaputra in India and Bangladesh, a lifeline for millions. The plan involves five dams along a 50‑km stretch where the river plunges 2,000 metres off the Tibetan Plateau. First power is expected to be generated in the early‑to‑mid 2030s, but beyond that and the price tag, China has published little information about how it intends to build the project. That lack of information is compounding fears about water security in India and Bangladesh, which rely on the Brahmaputra for irrigation, hydropower and drinking water. The chief minister of Arunachal Pradesh, which borders China, said earlier this year that the dam could dry out 80% of the river passing through the Indian state while potentially inundating downstream areas such as neighbouring Assam state. In addition to water, the dam will also mean less sediment flowing downstream, according to Michael Steckler, a professor at Columbia University. That sediment carries nutrients essential for agriculture on floodplains downstream.

Full explainer : China is building the world’s biggest hydropower dam. Why are neighboring countries worried?