In the present study, Seasonality and Species diversity of Phytoplankton studies were made on the Karagam Lake of Srikakulam District, Andhra Pradesh from November 2006 to October 2008. The phytoplankton population was represented by a Total taxa of 64 genera were recorded in this study. This includes Chlorophyceae (26 genera- 74 species), Bacillariophyceae (18 genera-41species), Cyanophyceae (17 genera-39 species) and Euglenophyceae (3 genera-8 species). The abundant algal forms belong to Volvocales (9 genera, 12 species), Chlorococcales (7 genera, 16 species), Conjugales (9 genera, 43 genera), Nostocales (9 genera, 18 species) in Karagam lake.