The occurrence, abundance and diversity of the phytoplankton community in a paddy – field wetland complex are influenced by nutrient concentrations, rainfall patterns, location and the nature of the physical environment. This also tends to affect water quality in the ecosystem. The biota differs greatly with the changes in the physico – chemical conditions in aquatic ecosystems. According to Reid (1961), the successful development and maintenance of a population of organisms depends upon harmonious ecological balance between environmental conditions and tolerance of the organisms to variations in one or more of these conditions. The pH in the study area was more acidic but for the 1988 (22 years old site), it was basic. This could be as a result of the rainfall pattern and the agricultural activities in the area.