Studies and diurnal variations of primary productivity in Sunderdam reservoir was conducted to evaluate the productive potentiality and the nature of community metabolism in the reservoir. Remarkable high values of gross and net productivity was recorded during winter months while minimum values in monsoon month. Abiotic factors like light intensity, water temperature, nutrients (Phosphate, Silicate and Nitrate) and biotic factors like phytoplankton density etc. influenced the productivity values. Production and Respiration (P/R) ratio was evaluated more than one (P/R >1), which referred to autotrophic nature of the reservoir. Besides, Net Daily Metabolism (NDM) revealed positive value in different seasons (0.169 — 0.307) confirmed the community metabolism was dominated by production and emphasized the importance of autochthonous input to the reservoir.