ExplainedArunachal Pradesh
The Siang dam explained: what the 11,000 MW project is, and why the Adi are resisting it
A bandh against the Siang Upper Multipurpose Project ended in a night of vandalism in Pasighat, and Pema Khandu has offered talks. What the dam is meant to do, how China's giant dam upstream comes into it, and why the people who live on the river say no.
The short answer
The Siang Upper Multipurpose Project (SUMP) is a proposed storage dam of about 11,000 MW on the Siang river in Arunachal Pradesh, the stretch of the Brahmaputra that enters India from Tibet. The Centre and the state say its reservoir, put at about 9 billion cubic metres, would protect India against sudden releases or withholding of water by China, which began building a far larger dam upstream in 2025. The Adi communities whose villages and farmland would be submerged say they were never asked for consent. NHPC's survey for a pre-feasibility report is still under way.
What is the Siang Upper Multipurpose Project?
It is a proposed giant dam and reservoir on the Siang, the river that becomes the Brahmaputra.
The Yarlung Tsangpo rises in Tibet, cuts through the Himalaya and enters Arunachal Pradesh as the Siang. Below Pasighat it joins other rivers in Assam and takes the name Brahmaputra. The Siang Upper Multipurpose Project, or SUMP, would put a dam across it in Upper Siang district, near Geku village, with an installed capacity of about 11,000 MW.
That would make it India’s largest hydropower project by a wide margin. The idea was first put forward by NITI Aayog in 2017, and in April 2022 the Centre asked the state-run hydropower company NHPC to carry out a pre-feasibility survey. Chief Minister Pema Khandu has said the reservoir would hold about 9 billion cubic metres of water, and estimates have put the cost at about ₹1.13 lakh crore.
Why is it called “multipurpose”?
Because the government says it is about water security, not only electricity.
“The SUMP is not just about generating power,” Khandu has said. He has argued that its real objective is “to save the Siang river and the communities that have depended on it for generations”, by keeping the river flowing in the dry season and absorbing floods.
The reason is upstream. In July 2025 China began building a hydropower project of about 60 GW on the lower Yarlung Tsangpo, roughly 30 km north of the Arunachal border, the largest of its kind in the world. Indian ministers have called it a potential “water bomb”: China could, in theory, hold back water or release it suddenly. A large Indian reservoir downstream is meant to act as a buffer against both. “China is unpredictable and can do anything,” Khandu said in December 2024.
There is no treaty between India and China on sharing the river’s water. An agreement under which China shared flood-season data on the Brahmaputra expired in June 2023 and had not been renewed.
Who would lose land?
Adi villages along the Siang, and the farmland they live on.
The project area is home to the Adi, one of Arunachal’s largest indigenous communities, who grow paddy, ginger and cardamom on the river terraces. Estimates of how many villages would be lost vary. One account puts the figure at 13 villages fully submerged; Gegong Jijong, president of the Siang Indigenous Farmers’ Forum, has said at least 27 villages in Siang and Upper Siang districts would be directly affected.
Villagers also fear the dam would trap the silt that the river carries to fields downstream.
Why are people protesting?
They say the project is being pushed on them without their consent.
Groups such as the Siang Indigenous Farmers’ Forum have protested since 2024, saying the survey work began without “prior, informed consent from the communities”. The authorities responded by deploying armed forces and police, which deepened the anger. “If the dam is built, we will lose everything,” Tabeng Siram, a member of the forum, has said.
On 23 October 2026 groups opposed to SUMP called a 12-hour bandh in Siang, Upper Siang and East Siang districts. It passed off largely peacefully during the day, but overnight a police station, the NHPC office and the homes of state BJP president Kaling Moyong and MLAs Oni Panyang and Ninong Ering in Pasighat were ransacked.
Do experts agree it would work?
Not all of them. Some environmental researchers point out that a hydropower dam is usually kept as full as possible to generate electricity, which leaves little room to soak up a sudden flood. The narrow, deep valley also limits how much buffering the reservoir could provide. Others argue that India must build to secure its claim to the river’s water, given how far China has moved ahead.
What happens next?
Talks, if both sides turn up. Khandu said on Saturday that the government’s “doors are always open” and offered to meet the dam’s opponents in Itanagar, Pasighat or anywhere else they choose. He said he would spend the month in the Siang region until the pre-feasibility report process is complete.
That report is only the first step. A full project report, environmental and forest clearances and public hearings would follow before any construction could begin, and each of those stages will need the consent the Adi say they have never been asked for.