The landslide blocked a diversion tunnel in the river, leading to a reduction in the water flow.
Massive protests have erupted in Assam after a massive landslide hit an under-construction dam in Arunachal Pradesh on Friday, affecting a 2,000 megawatt (MW) hydroelectric project and reducing water flow in Assam's Subansiri river.
"We have already seen the adverse effect of dams in Sikkim, how it breached and so many people died. Now this sudden reduction of water in Subansiri has made us worried, we don't sleep the entire night since we live beside the river," one of the protesting villagers, Deben Dutta, told NDTV.
Another protesting villager Maya Nath said, "We are worried, suddenly there might be a huge rush of water, we are keeping a constant watch on the river, we are not sending children to school, we have kept boats prepared, we are in panic mode".
This comes weeks after another disaster hit the Northeast - a dam breach in Sikkim following a glacial lake outburst caused massive flash floods and several deaths. The landslide has alarmed the authorities in Assam's Lakhimpur district, downstream of the dam in Arunachal Pradesh.
The dam at the 2,000 megawatts lower Subansiri Hydropower project is one of the mega dams being developed in Arunachal Pradesh. The landslide blocked a diversion tunnel in the Subansiri river, leading to a drastic reduction in the downstream water flow.
"This was the only diversion tunnel in use at the Subansiri Lower Hydroelectric Project as the other four diversion tunnels had already been blocked earlier," the National Hydroelectric Power Corporation, the mega dam developer, said in a statement.
" We accept that we are facing some hurdles and now the focus is to close the gate of diversion tunnels so that landslides don't affect them" AN Mohammad, senior consultant, NHPC, told reporters at the dam site.
The government has issued an advisory, asking people to restrain from activities like fishing, swimming, bathing and boating. People have also been asked to keep their cattle away from the river.
Earlier, landslides blocked four other tunnels.
In April last year, the powerhouse protection wall collapsed due to tail race channel construction activities.
Over the past three years, the project site has been hit by four major landslides.
The latest incident has added to the growing concerns over mega dams on rivers in the eastern Himalayan belt.
"The recent led by hydropower projects in the eastern Himalayas has once again raised the larger issue of how environmental risks are explored before developing hydropower projects. For example, the glacial lake outburst incident in Sikkim, where the dam got washed away due to a similar case of the lower Subansiri project, where for years people have raised concern about not only of downstream impact but also environmental risk factors," said Neeraj Vagholikar, a researcher on Environment and Hydropower.
Subansiri, being the largest tributary of the Bramhaputra, influences a larger ecosystem. If it takes time to restore the river flow, its impact could be wide-ranging.