The present study deals with the diversity and distribution of aquatic insects from Sothuparai Reservoir. It is located at the foothills of the Western Ghats. The aquatic entamofauna were sampled systematically and randomly using standard protocols. The aquatic insects act as an indicator species to monitor the environmental pollution. Ephemeropteran were most diverse and its presence indicative of good water quality. The abundance of organic pollution tolerant Baetis were found in downstream, nearer to human settlements. The physico chemical variations of water taken into account for the study were found to be influencing the distribution of aquatic insects. It is suggested that routine bio monitoring of the reservoir using aquatic insect indicators will facilitate better conservation and management.