A glacial lake outburst flood (GLOF) at Shintaphu Lake in Gasa district, Bhutan, has triggered a flood alert across north Bengal, with the West Bengal government evacuating residents along the Sankosh River to relief camps on 30 October 2026. The sudden discharge of glacial water is raising fears of significant inundation in districts bordering Bhutan.

How the GLOF Unfolded

On Thursday evening, a large volume of water surged out of Shintaphu Lake, a glacial water body in Gasa district. The outflow damaged infrastructure near the Gasa Shachu hot spring and caused the Mo Chhu River — one of the two largest tributaries of the Sankosh — to rise sharply. A stretch of the Punakha-Gasa road was reportedly washed away, disrupting traffic, while an irrigation project in Punakha suffered partial damage. The full extent of damage within Bhutan is not yet known, according to preliminary reports.

Although an alert was issued on Thursday night, the Sankosh's water level had not risen significantly by Friday morning. By afternoon, however, water levels began climbing sharply across several stretches, prompting heightened concern on both sides of the border.

What the Government Said

State Minister Nisith Pramanik confirmed that water from the burst lake was flowing downstream through the Mo Chhu River and heading toward the Sankosh River. 'Residents living along the Sankosh River and its tributaries have been alerted. They have been advised to move to a safe place immediately to ensure their safety,' Pramanik said.

The minister added that floodwater was expected to reach the plains within 5 to 6 hours of the alert, 'creating a high risk of significant flooding in the area.' He confirmed that the State Disaster Management Team had been activated, the National Disaster Response Force (NDRF) had been notified, and disaster management volunteers had been deployed on-site.

Evacuations and Ground Situation

Residents along the Sankosh in north Bengal districts bordering Bhutan were evacuated to relief camps. Many spent the night on the national highway out of fear. On Friday morning, with the river appearing calm, several residents of Kumargram block in Alipurduar district attempted to return home. However, as the Sankosh's waters turned increasingly muddy — a sign of elevated sediment load from upstream — many reversed course and returned to the camps.

Why Shintaphu Lake Is a Known Hazard

Shintaphu is among 17 lakes in Bhutan officially identified as high-risk due to glacial instability. This is not the first time it has unleashed downstream chaos: on 26 August 2021, a sudden rise in the lake's water level caused the Mo Chhu to overflow, change its course, and wash away the Gasa Shachu hot spring. The recurrence underlines the escalating threat of GLOFs in the eastern Himalayan region as glaciers destabilise under rising temperatures.

The Torsa, Jaldhaka, Sankosh, and Raidak rivers all enter north Bengal from Bhutan, making the region structurally vulnerable to any upstream glacial event. The Sankosh — known as the Puna Tsang Chhu in Bhutan — originates in northern Bhutan, flows through Assam and West Bengal, and eventually joins the Brahmaputra. A substantial surge in the Mo Chhu therefore propagates downstream, amplifying flood risk well into the Bengal plains.

What Happens Next

Authorities are closely monitoring river levels across the affected districts. The situation in Alipurduar and neighbouring areas will remain critical over the coming hours as the full quantum of released water works its way downstream. With the monsoon season still active and glacial outburst risk undiminished, this episode is likely to renew calls for a robust early-warning system linking Bhutanese hydrological stations directly to Bengal's disaster management network.