During Monsoon season, especially from June to September, the volume of water in the river and its tributaries rises heavily due to continuous rainfall in Sikkim.
Its confluence with Teesta River is immediately downstream of Rangpo town, the confluence point is known as Indrakil Prayag.
At the town of Rangpo, there is a bridge across River Rangpo, the bridge is called Atal Setu Bridge or Rangpo IBM Bridge and it is the longest bridge of Sikkim.
Course
The river originates from Lake Menmecho near Dzuluk in Gangtok district of Sikkim. It flows down towards the villages of Pakyong District like Latuk, Rolep, Losing, Chochenpheri, Chujachen and reaches the town of Rongli, where it is joined by a river called Rongli Khola. It further flows through villages of Sudunglakha, Mulukay, Bering, Tareythang, Tarpin where the river is fed my many tributaries like River Richu, River Donok, River Ralang, River Pachey, River Khaarey and it reaches the town of Rorathang, where it is joined by one of its largest tributary- Reshi River. From here the river forms border between Pakyong District of Sikkim and Kalimpong District of West Bengal, flowing through villages like Bhasmay, Kashyong, Kumrek, Lower Mansong, Chanatar etc and other small rivers like Kumrek Khola, Pool Khola, etc., join in and the river finally reaches the town of Rangpo, where it joins river Teesta.
