The present study deals with the phytoplankton dynamics, biomass and physicochemical features in freshwater reservoir, Tillari, western India. The reservoir experience seasonal stratification and mixing associated and changes in the biogeochemical aspects especially the phytoplankton community and chlorophyll a. Depth affected the behavior of the phytoplankton associations. Buildup in phytoplankton biomass was observed in the upper strata of the water column (epilimnion) during the monsoon period (June-July) and winter (December) as a result of nutrient enrichment from the hypolimnion. Among nutrients, nitrate was associated with buildup of Chl a during summer in the epilimnion (r2 = 0.7). A total of about 91 phytoplankton species were identified with major contribution by charophytes and chlorophytes. The dominant phytoplankton species belonged to genera Staurastrum, Cosmarium, Aulacoseira, Nephrocytium and Shroederia. Charophytes made a remarkable presence during the whole study period in the well oxygenated epilimnion as well as in the hypolimnion with relatively low oxygen. Diatom, the major silica sinking group was relatively less abundant. Keeping the importance of the reservoir in view, the understanding phytoplankton community from this poorly explored reservoir with respect to influencing factors is a very vital baseline information. Thus, to design and evaluate the management strategies for the reservoir, continuous monitoring and processes studies is warranted.