A glacial lake outburst flood (GLOF) at Shintaphu Lake in northwestern Bhutan on Thursday evening, 30 October 2025, has triggered flash flood warnings across parts of West Bengal and Assam, with authorities closely monitoring river corridors flowing downstream toward both states. The event originated in Bhutan's Gasa district and has already damaged infrastructure, though no casualties have been reported.

How the Flood Unfolded

The floodwaters swept through Gasa Tshachu, a popular natural hot spring located near the Mo Chhu River, washing away infrastructure at the site. Notably, Gasa Tshachu had suffered near-identical damage previously — on 26 August 2021, a swollen Mo Chhu changed course toward the hot spring during a flash flood. The area had been evacuated before Thursday's surge arrived, which officials credit with preventing any loss of life.

According to reports, the floodwaters crossed Srigang in Kabesa Gewog, roughly eight kilometres from the historic Punakha Dzong, raising alarm among downstream communities. Shintaphu Lake, situated at the headwaters of the Mo Chhu River, is listed among Bhutan's 17 glacial lakes classified as potentially dangerous due to their size, location, and susceptibility to rapid drainage.

Districts on Alert in West Bengal and Assam

Bhutan formally alerted the administrations of West Bengal and Assam about the downstream threat. In Assam, Dhubri district has been flagged as vulnerable. In West Bengal, the at-risk zones include the Darjeeling hills, Alipurduar, and Jalpaiguri. The Cooch Behar administration separately alerted residents living along the banks of the Sankosh River, which originates in northern Bhutan and drains into the broader Brahmaputra river system.

Authorities urged residents to exercise caution while assuring them that precautionary measures were already in place. Amit Kumar Shaw, Superintendent of Police of Alipurduar Police District, appealed for calm on Thursday, saying: 'People are slightly in panic, and my appeal to everyone is that there is no need to panic in any way. We are in alert mode, the administration is fully prompt, and all agencies are actively working, so there is no issue. We hope that within two to three hours, we will reach a resolution and address whatever trouble the public is facing.'

Infrastructure Damage in Bhutan

Beyond the hot spring complex, the GLOF caused broader infrastructure damage inside Bhutan. An official press release confirmed that a solar-powered irrigation lifting system installed earlier this year in the Dochhukha-Dzomlingthang-Ritsa Chiwog area under Guma Gewog in Punakha was partially damaged by the surge in the Mo Chhu. A local leader confirmed the system had stopped functioning, though officials said the full extent of the damage was yet to be determined.

Additionally, flood-borne debris blanketed a section of the Punakha-Gasa Highway in the Dzomlingthang area, potentially disrupting road connectivity between the two districts.

The Climate Context

A glacial lake outburst flood occurs when water stored in a glacially formed lake is suddenly released — typically after the failure of a natural ice or moraine dam. Triggering factors include heavy rainfall, landslides, avalanches, seismic activity, or rapid glacial melt. Rising temperatures linked to human-induced climate change are accelerating glacier retreat across the Himalayas, increasing both the number and size of glacial lakes and heightening the risk of future GLOFs. This is not an isolated incident: the broader Himalayan arc has recorded a significant uptick in GLOF events over the past two decades, with communities in northeastern India, Nepal, and Bhutan repeatedly bearing the consequences.

With floodwaters still moving through the river system, authorities in all three jurisdictions are expected to remain on heightened alert through Friday.