An attempt was made to study the microbial population of Veeranam lake water, Tamil Nadu. Water samples were collected monthly at five locations and analysed for the microbial population by MPN technique during the year from July 2011 – June 2012. The samples showed the presence of bacteria, fungi and actinomycetes. The monthly average values were taken for statistical analysis. The percentage distribution of microorganisms varied from 75.04 to 77.36% bacteria, 0.79 to 2.05% fungi and 21.23 to 24.17% actinomycetes. The concentration of bacteria and actinomycetes were lower during the premonsoon and gradually increased in monsoon, post monsoon and summer and the fungi concentration were maximum during postmonsoon and gradually reduced in monsoon, premonsoon and summer. It indicates that the water for drinking is pre-treated before consumption.