The Nepal-China border is once again at risk of flooding after China warned Nepal that a newly formed barrier lake upstream could breach within three days, potentially sending another powerful wave of water downstream.
A glacier collapse on August 26 caused a deadly flood in Nepal’s Bhotekoshi river, while a separate mudslide buried China’s Gyirong Port crossing on the same day. With both countries already dealing with the aftermath, the possibility of the new lake bursting has raised concerns about another major flood downstream.
WHAT TRIGGERED THE BHOTEKOSHI FLOOD IN NEPAL?
Nepal’s Department of Hydrology and Meteorology (DHM) said the flood was not triggered by rainfall. Satellite imagery suggests that a massive section of glacier, believed to have broken off from the northern face of Langtang Lirung at an altitude of around 5,200 metres, plunged nearly 1,200 metres into the Lhende river, a tributary of the Bhotekoshi.
The falling ice and rocks blocked the narrow valley, effectively creating a natural dam. When the blockage gave way, it unleashed a powerful torrent carrying mud, ice and boulders towards Rasuwa, Nuwakot, Dhading, Gorkha and Chitwan.
WHAT CAUSED THE DISASTER ON THE CHINESE SIDE?
That same morning, a separate mudslide occurred near Gyirong Port in China’s Xizang region, an important trade route between China and Nepal. Chinese state broadcaster CCTV reported that mud reached depths of more than five feet in some areas, disrupting roads and communication links.
By Thursday morning, three people had been confirmed dead and 558 were still missing on the Chinese side. Chinese President Xi Jinping directed authorities to launch a comprehensive search and rescue operation. However, officials have not officially established whether the mudslide and the Bhotekoshi flood were connected.
COULD ANOTHER FLOOD HIT NEPAL?
China’s Ministry of Water Resources reported that a barrier lake had formed near the meeting point of the Chhochen Khola and Purepu Tsangpo rivers. By Thursday morning, the lake contained around 2 million cubic metres of water and had already begun overflowing.
Officials estimate that another 3 million cubic metres of water could enter the lake over the next three days, creating a significant risk that the barrier could collapse.
Chinese engineers are conducting flood simulations to prepare for a possible breach. Meanwhile, Nepalese authorities have urged people living along the Bhotekoshi, Trishuli and Narayani rivers to avoid riverbanks until further notice.
HOW LARGE WAS THE FIRST FLOOD WAVE?
According to DHM data, the flood entered Nepal at around 9 am on Wednesday before reaching its peak at Devghat in Chitwan later that afternoon. The flow there was estimated at nearly 5,850 cubic metres per second.
Approximately 20 million cubic metres of additional water passed through Devghat. That volume was several times greater than the amount involved in the 1985 Dig Tsho glacial lake outburst flood in the Everest region. The flood travelled nearly 170 kilometres downstream within just a few hours.
WHY ARE SUCH FLOODS BECOMING MORE FREQUENT IN THE HIMALAYAS?
The latest incident is the second major flood on the same stretch in just 14 months. A similar event occurred in July 2025 and was associated with a lake located above a glacier.
According to the International Centre for Integrated Mountain Development, the number of glacial lakes across the Himalayas has increased from roughly 1,900 to more than 2,600 since 2005. As the Himalayan region is warming faster than the global average, the growing number of unstable glacial lakes is increasing the risk of sudden and destructive floods on both sides of the Nepal-China border.
