This study is aimed at assessing the effect of seasons on quality of lake water in relation to changes in fish, plankton abundance and environmental variables. Standard methods were used to analyze monthly fish, plankton and water samples collected from Ikwori Lake during wet and dry seasons for 24 months (January 2008 to December 2009). All measured water parameters except dissolved oxygen (3.3 ± 0.10mgl-1), total dissolved solids (103.2 ± 2.22mgl-1), acidity (4.44 ± 3.91mgl-1), color (60.33 ± 8.38pt. co) and pH (5.8 ± 0.119) showed significant seasonal variation. The highest values of the parameters occur between February and March (dry season) and lowest between May and August (wet season). In addition, total phytoplankton (cells/litre), were significantly more during the dry season than the wet. Out of 16 fish species sampled, 7 species were restricted to dry season, only one i.e. Polypterus senegalus was recorded in the wet while 8 species occurred in both seasons. Seasonal differentiation in the richness and diversity indices of all species sampled revealed higher values for the dry season than the wet. Therefore, the influence of season is important in the management of water quality, plankton and fish production of the aquatic system.