The presence of the blue – green algae, as the most abundant genera, indicates that the water is not potable except after proper treatment. The blue – green algal blooms gave a dark green paint – like appearance in water, which is indicative of eutrophiction. The nitrogen and phosphorus levels were higher than normal levels for potable water. According to Williams and Tonnessen (2000), the increased nitrate and phosphorous concentrations have been the drive increasing phytoplankton levels. This is because they are both basic necessities for phytoplankton activities. The two most common consequences of nitrogen and phosphorus saturation of surface waters are eutrophication and acidification (Stoddard, 1994). This high acidity is evident at almost all the paddy sites. McKnight et al. (1994) suggested that acidification of the Green Lake may result in a shift in phytoplankton productivity and community composition.