This chapter exhibits a robust water qualityWater quality assessment of the water samples collected from 12 sampling sites of Mahananda (7) and Balason RiverBalason river (5) for 3 consecutive flood and non-flood seasons. The sampling sites are selected based on the intensity of human interventionHuman intervention and in accordance with this, only 4 were selected on the hilly region (2 each for Mahananda and Balason). After prior analysis of the West Bengal Pollution Control Board (WBPCB)West Bengal Pollution Control Board (WBPCB) data, it is identified that the pollution is biotic and accordingly a total of 13 parameters are selected. To perform the water quality analysis, 3 water qualityWater quality indices are chosen, namely the Overall Index of Pollution (OIP)Overall Index of Pollution (OIP), the Organic Pollution Index (OPI)Organic Pollution Index (OPI) and the Canadian Council of Ministers of the Environment Water Quality Index (CCMEWQI). The CCME WQICCME WQI was further analyzed for human consumption, bathing and fish liveabilityFish liveability. Results showed that all the pollutants mostly have a higher concentration on the unconfined reaches, especially the Mahananda RiverMahananda river flowing through the Siliguri Municipal CorporationSiliguri municipal corporation (SMC). No sampling points are observed with consumable water, the rivers flowing through the hilly region and adjacent to that are suitable for bathing and except for one sampling site situated at SMC, all other sampling sites were observed with liveable conditions for fish.