The River Teesta is said to be the lifeline of the Indian state of Sikkim, flowing for almost the entire length of the state and carving out verdant Himalayan temperate and tropical river valleys. The emerald-coloured river then forms the border between Sikkim and West Bengal before joining the Brahmaputra as a tributary in Bangladesh. Total length of the river is 315 kilometres (196 mi).
The river originates from Cholamo Lake at an elevation of 5,330 m (17,487 ft) above sea level in the Himalayas. This lake lies to the north of the Donkia pass near Shetschen, where the summit of the pass is about eight kilometres north-east of Darjeeling.
Through its course, river has carved out ravines and gorges in Sikkim meandering through the hills with the hill station Kalimpong lying just off the river. Variegated vegetation can be seen along this route. At lower elevations, tropical deciduous trees and shrubs cover the surrounding hills; alpine vegetation is seen at the upper altitudes. The river is flanked by white sand which is used by the construction industry in the region. Large boulders in and around the waters make it ideal for rafting enthusiasts.
During the monsoons this humble river distends its banks; both in size and turbulence. Landslides in this region often dam up parts of the river in this season.