53 species belonging to 26 families were identified in the different paddy field sites. Chlorophyta was the most common class with the most abundant number of species 26.42% followed by bacillariophyta and dinophyta (20.76%) which are more frequent as the paddy – fields grow older (Figure 2). The most abundant families were the Dinophyceae and Nitzschiaceae, while the least abundant was the Ulotrichaceae, Podolampaceae and Cladophoraceae. The most abundant species were Microcystis aeruginosa (in the 1975 site), Anacystis sp. (in the 1977 site), Chlorococcus disperses (in the 1988 site),