Water pollution is the main cause for diminishing of local small rivers in India. Excessive water pollution causes an increase in the biological oxygen demand (BOD) and chemical oxygen demand (COD), which affects the life of aquatic flora. Daha River, a 96 Kilometer small river in the north Bihar region of India originates from Sasamusa in Gopalganj district. In this study, we have monitored the water quality of this river by using macroinvertebrates present in the water system as a biological indicator. In the random sampling of water from Daha River provided evidences that the water condition of the Daha River is highly polluted due to sugar industry effluents, agricultural activities, and municipal waste which are the main troubling agents of the physiochemical property of this river, increasing the BOD of water and the increasing number of macroinvertebrates. This study provided scientific evidence to attract the concern of several government organizations to save this river as well as important aquatic flora and fauna present in the water body of this river.