(Feature Image: Shintaphu Lake. Source: The Bhutanese. It is not clear whether the image is old or post Oct 2026 GLOF)
A glacial lake outburst flood (GLOF) was reported from Shintaphu Lake in Bhutan’s Gasa district on the evening of Oct. 29, 2026. The disaster triggered flash flood alerts in downstream areas of Bhutan and India. Bhutan’s National Centre for Hydrology and Meteorology (NCHM) is stated to be monitoring the situation. The cause, volume of water released and full extent of the damage are still being assessed.
About Shintaphu Lake: Shintaphu is a high-altitude glacial lake near Wakila Mountain in the Lungo area of Laya Gewog, Gasa district. It lies at the headwaters of the Mo Chhu (river). The lake is officially listed among Bhutan’s 17 potentially dangerous glacial lakes and requires continued monitoring. Bhutanese specialists studied the lake between May and June 2023. The assessment covered the main and upper lakes, surrounding terrain, moraine barriers and the glacier feeding the lake.
The lake is spelt Sintaphu in NCHM’s technical records and marked as Shangtaphu in Google Earth (GE) imagery. GE imagery from April 2019 shows two lakes near the glacier snout. The larger, lower lake covers approximately 23.53 hectares area while the smaller upper lake covers about 8 hectares.
According to the International Centre for Integrated Mountain Development (ICIMOD), the lake contained an estimated 6–7 million cubic metres of water before the outburst, equivalent to approximately 2,400–2,800 Olympic-sized swimming pools. The actual volume released is still under assessment.
River System: Water from Shintaphu Lake enters the Mo Chhu which flows south through Gasa and Punakha districts. At Punakha, the Mo Chhu joins the Pho Chhu to form the Punatsangchhu. The river enters India as the Sankosh and is also known as the Gangadhar in parts of the Assam plains. It eventually joins the Brahmaputra in Dhubri district of Assam. The total length of river from Shintaphu to Brahmaputra is about 220 km.
This transboundary river connection prompted flood alerts in downstream areas of West Bengal and Assam. Communities near vulnerable sections of the Sankosh were advised to remain alert and move away from riverbanks where necessary.
Impact in Bhutan: Floodwater washed away a section of the Punakha–Gasa Secondary National Highway near 31.85 km forcing its closure. Travelers were advised to postpone non-essential journeys and check for alternative routes.
The flood reached Taktsemakhang at around 8:15 pm on Oct. 29, about 20 km downstream the GLOF origin point. It damaged a section of the road serving Laya and disrupted access to the remote highland community. People in vulnerable downstream locations were moved to safer places, and warning sirens were activated.
So far, there no death or injuries reported in the incident. The cause of the outburst, the volume of water & debris released and the full extent of the damage were still being assessed.
Artificial Lake: As per updates in the morning of Oct. 30, the flash flood debris have blocked the mouth of the Shingchala Chhu near Taktsemakhang, forming a new artificial lake. The site is about 20 km downstream of Shintaphu Lake. The lake is reported to be increasing in size. Authorities alerted people in downstream districts including Punakha, Wangdue, Tsirang and Dagana about the possibility of another flood.
Bhutan’s Prime Minister Lyonchhen Dasho Tshering Tobgay has personally inspected the blockage on Oct. 30. As per him the lake is not highly dangerous and Govt is considering controlled blasting to drain it safely.
A video footage of the inspection shows water continuing to flow through a section of the debris blockage, indicating that the river has not been completely blocked. However, the stability of the blockage and the risk of a sudden release remain important concerns.
Hydro Power Projects: The Punatsangchhu river basin hosts two major India–Bhutan joint-venture hydropower projects including 1200 MW Punatsangchhu-I and 1020 MW Punatsangchhu-II. Both the projects are vulnerable to potential GLOF-related risks.
Punatsangchhu-II, located in Wangdue Phodrang district, was fully commissioned in Aug. 2025 after much delay. Following the Oct. 29 GLOF, the project reportedly suspended power generation and opened its spillway gates as a precautionary measure to manage the flood surge and debris. However, no official assessment of damage to its infrastructure has been reported.
Punatsangchhu-I project is under construction in Wangdue Phodrang Dzongkhag. Approved in 2008, it was initially scheduled for commissioning in 2015. However, the project has faced repeated delays due to geological challenges and disasters at dam site in 2013, 2016 and 2019. Work on the project was suspended in 2019 and resumed after a gap 7 years in April 2026. No specific information on GLOF-related damage or disruption at Punatsangchhu-I has been reported so far.
The powerhouse of the 64 MW Basochhu Hydropower project is also located near the confluence of the Basochhu and Punatsangchhu rivers in Wangdue Phodrang district. No official information on the impact of the GLOF on this project is available at the time of writing.
Impact in India: In the early hours of 30 October 2026, the Central Water Commission (CWC) issued a special flood advisory following reports of the GLOF. It warned of a possible sudden rise in the Sankosh River, with potential impacts in Alipurduar district of West Bengal and Dhubri district of Assam. The advisory estimated that floodwater could reach the Indian border within 6–8 hours. The CWC advised local authorities to remain alert, monitor river levels and take necessary precautionary measures.
Authorities in West Bengal and Assam has subsequently alerted residents in vulnerable areas along the Sankosh. In Alipurduar, residents of some riverbank villages have been reported leaving their homes with their cattle following evacuation orders issued late on Oct. 29. The Assam government also placed Dhubri district on alert and said it was closely monitoring the situation.
Flood Monitoring Station: The CWC operates three flood monitoring stations along the Sankosh River including two level monitoring sites and one level forecast site. The Sankosh LRP is located in Alipurduar district, West Bengal while Golokganj (level forecast) and Baladoba are in Dhubri district, Assam.
As of 18:00 hour, Oct. 30, there is marginal rise in water level at Sankosh LRP site and the water level is stable at remaining two sites in Dhuburi district. The details of the site and water level can be seen in table below.
| SN | Site | District | HFL/ Date | Flood level | Remark |
| 1 | Sankosh LRP | Alipurduar | 49.25 m/ 09.07.2017 | 44.54 m/ 17:00 hr/ 30.10.2026 | 0.62 m rise between 07:00 to 10:00 hr on 30.10.26 |
| 2 | Golokganj | Dhuburi | 30.95 m/ 08.09.2007 | 27.1 m/ 17:00 hr/ 30.10.26 | 1.84 below warning level. |
| 3 | Baladoba | Duburi | 30.70 m/ 08.09.2007 | 25.43 m/ 18:00 hr/ 30.10.26 | 5.27 m below HFL |
The readings of CWC’s three sites indicate that the water level in the river is quite normal and presently there is no cause of concern. It is not clear whether the GLOF surge has reached or passed through these sites. It is also unclear whether the CWC’s estimated 6–8-hour arrival window was accurate. The status of the artificial lake and its potential impact on downstream areas in Bhutan also remain uncertain.
There are several important questions about this GLOF event. It is not yet clear whether Shintaphu lake has breached completely or partially or it simply overflowed. The trigger and volume of water & debris released, the stability of the original lake and the full extent of damage to roads, infrastructure, Hydropower projects, livestock and property in Bhutan also remain to be established. The size and stability of the newly formed artificial lake at Taktsemakhang and the risk of another sudden release, require particular attention.
It is also important to assess how effectively Bhutan’s monitoring and early-warning systems performed and whether and to what extent the GLOF has affected hydropower infrastructure and operations in the Punatsangchhu basin. Field investigations, hydrological monitoring data and satellite imagery will be essential to establish the sequence of events and assess the full impact of the GLOF.
SANDRP
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