River Rangpo is a river in the Indian state of Sikkim. A tributary of the Teesta River, it originates from Menmecho Lake near Dzuluk and flows through Rongli and Pakyong subdivision villages in Pakyong District towards Rorathang, Kumrek and Rangpo. The river demarcates the border between Pakyong District of Sikkim and Kalimpong district of West Bengal from Rorathang to Rangpo. At the town of Rangpo, the river joins river Teesta. The Rangpo is the third largest river of Sikkim after Teesta and Rangeet. Atal Setu Bridge the longest roadway bridge of Sikkim is over River Rangpo.

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.