Present study was conducted in river Varuna in Varanasi. Three types of small scale industries were located which pour their effluents directly into the river. Excepting Site I, which was the control Site all the other Sites were polluted. Site 2 consisted of small scale industries, Site 3 automobile servicing stations and Site 4 as dyeing industries. All the industries released chemical effluents which were discharged into the river Varuna directly. Every chemical effects pH of the medium, which ultimately affect the life of flora and fauna, thus affecting the biodiversity. Therefore, at all the four sites the study of pH variation was conducted for complete one year. As aresult, regular variation in pH of the river water was found. Highest acidity, i.e. lowest pH was recorded at all the sites,during summer, followed by winter. The river water was found to be alkaline during rainy season. Acidity of the water during most part of the study was contributed to the industrial effluents.