On 4 October 2023, heavy rains caused the glacial South Lhonak lake in Sikkim, a state in northeastern India, to breach its banks, causing a glacial lake outburst flood. The flood reached the Teesta III Dam at Chungthang at midnight, before its gates could be opened, destroying the dam in minutes. Water levels downstream in the River Teesta rose by up to 20 feet (6.1 m), causing widespread damage.

Teesta River is a 414 km (257 mi) long river that rises in the Pauhunri Mountain of eastern Himalayas, flows through the Indian states of Sikkim and West Bengal and subsequently enters Bangladesh through Rangpur division. In Bangladesh, it merges with Brahmaputra River which after meeting some other major rivers of the Bengal delta finally falls into the Bay of Bengal. It drains an area of 12,540 km2 (4,840 sq mi). In India, the Teesta flows through Mangan District, Gangtok District, Pakyong District, Kalimpong district, Darjeeling District, Jalpaiguri District, Cooch Behar districts and the cities of Rangpo, Jalpaiguri and Mekhliganj. In Bangladesh, it flows through Lalmonirhat District, Rangpur District, Kurigram District and Gaibandha District. It joins the Brahmaputra River at Phulchhari Upazila in Bangladesh. 305 km (190 mi) of the river lies in India and 109 km (68 mi) in Bangladesh. The Teesta is the largest river of Sikkim and second largest river of West Bengal after the Ganges.