The algae composition and physico-chemical parameters of Awon Reservoir were investigated for a period of four months (wet and dry seasons), this was done to examine the effect of seasonal variation on phytoplankton. The algae comprised a total of twenty-two species belonging to four divisions: bacillariophyta, chlorophyta, euglenophyta and cyanophyta.Navicula meniceculus, Gyrosigma scalproides, Closterium archerianum and C. dianae were the dominant species. The physico-chemical parameters determined were higher in the dry season than wet season. The values of physico-chemical obtained fell within the maximum allowable limit set by United Environment Protection Agency.