River Kopili, regarded as one of the most important Southern bank tributaries of the mighty river Brahmaputra, is facing a tremendous pollution threat from its riparian areas, especially in its upper stretches due to anthropogenic activities. The Central Pollution Control Board (CPCB) in one of its report has placed the Kopili river in 4th rank among the 56 most polluted river of North-East region. The results of the present study showed that water quality index [1] of the river ranges from poor to unsuitable quality of water for drinking in almost all the five sampling stations. The water quality found to be deteriorated during winter season with an average WQI value of 81.88 as compared to pre-monsoon and monsoon season with an average value of 67.13 and 80.12 respectively. According to the water quality index, station 4 and 5 are recorded to be the most polluted stations among the study area. Thus, all the above analysis showed that the riverine ecosystem is moderately polluted, which may degrade further if proper management of the riverine ecosystem is not initiated timely, which is the need of the hour to sustain the environmental integrity of the river Kopili.