Monsoon Havoc Escalates as Landslide Dams Arunachal River, Triggering Flash Flood Alert in Assam

The relentless monsoon has unleashed a fresh crisis in India’s Northeast after a massive landslide in Arunachal Pradesh’s Lower Siang district blocked the flow of the Siji river, creating a temporary natural dam that authorities fear could collapse at any moment and trigger a devastating flash flood downstream.

The landslide, triggered by incessant rainfall, has obstructed the river near the Siji-Magi Block Point, a short distance upstream of Likabali town on the Arunachal-Assam border. The blockage has resulted in the formation of an artificial lake, with rapidly accumulating water significantly increasing pressure on the debris barrier.

Officials have warned that if the makeshift dam gives way, an intense wall of water could surge downstream without warning, posing a serious threat to lives, homes, livestock, bridges, roads and other public infrastructure along the river’s course.

Authorities issue emergency alerts as downstream communities brace for danger

The district administration has placed residents of Likabali and villages situated along the Siji river, which flows into Assam as the Gai river, on high alert. Authorities have advised people to stay away from riverbanks, avoid unnecessary movement near the water, and remain prepared for immediate evacuation should conditions deteriorate.

Residents have also been asked to closely monitor any sudden rise in water levels, unusual sounds or visible weakening of the debris blockage and immediately inform the nearest administrative or police authorities.

The warning comes as Assam continues to battle worsening flood conditions. In neighbouring Dhemaji district alone, floodwaters have affected four revenue circles, Jonai, Sissiborgaon, Dhemaji and Gogamukh, impacting 15,483 people across 69 villages.

The destruction has extended well beyond inundated settlements. A railway bridge over the Simen river has collapsed, an iron bridge has been washed away, while embankments protecting stretches of National Highway 52 have suffered extensive erosion, disrupting connectivity across the region.

Rescue efforts continue as rains cripple connectivity across Arunachal

The wider humanitarian situation in Arunachal Pradesh remains grim. Rescue teams are continuing their search for three people, including a minor, who have remained missing since flash floods struck a hydropower project colony in Keyi Panyor district on June 24. Two bodies have already been recovered from the disaster site.

Elsewhere, torrential rainfall and cloudburst-induced flooding have left a trail of destruction across multiple districts. In East Siang district, nine major road links have either been washed away or rendered impassable by landslides and mudslides. Only two of the eleven critical routes monitored by authorities have so far been reopened.

The worst damage has been reported on the Pasighat-Runne-Takilalug Road, where floodwaters washed away one side of the Letong Bridge, while the strategically important Pasighat-Yagrung-Ledum-Tene Road remains closed indefinitely. Several other key routes connecting Pasighat with Pangin, Mariyang-Yingkiong and Mebo-Dambuk-Bomjir continue to remain blocked.

The India Meteorological Department has warned of rainfall exceeding 200 mm in parts of Arunachal Pradesh, prompting fresh advisories against non-essential travel.

Amid the widespread devastation, the Border Roads Organisation has provided one rare positive development. Personnel restored the crucial Kimin-Potin Road within just 36 hours after multiple landslides, flash floods and road breaches had severed connectivity. The route serves as a critical lifeline for five higher-altitude districts, where heavy rain had buried roads under mud, uprooted trees, boulders and washed-away sections, leaving several strategic locations completely isolated.