The Lachung River is a tributary of the Teesta River situated in the North Indian state of Sikkim. It is a boss tributary of the Teesta, which is a critical waterway in Sikkim alongside Rangeet River. The town of Lachung is perched on the rocky bank of the stream more or less 23 kilometers (14 mi) from Chungthang. It is at Chungthang where the Lachung and Lachen streams meet and offer ascent to the Teesta. The waterway is 2,500 meters (8,200 ft) above sea level. The waterway has its source in a lake, somewhere down in the Himalayas close to the Indo-China fringe. The worn out scopes of the mountain make the spot difficult to reach. From here, the waterway streams down in a south-westerly bearing and joins with another obscure stream at a spot simply above Lachung town. The tributary waterway is additionally a thin one with little water in the winter. The waterway proceeds with its course downwards through the Lachung valley till it meets River Lachen close to Chungthang.