The changes in phytoplankton and physico-chemical characters of LakeManzala were studied during the period from January 2003 and March 2004. Water samples collected from ten stations representing four sectors. The physico-chemical is highly loaded of different source of pollution. Phytoplankton standing crop and diversity were highly affected by the high amount of pollution effluents into the Lake. The species composition of the main algal groups showed distinct variations. The dominance of algal groups at the Lake was in the following order Bacillariophyta (54.75 %), Chlorophyta (39.31 %) and Cyanobacteria (4.83 %) were the most dominant groups. However, Dinophyta (0.73 %) and Euglenophyta (0.37 %) were not detected during summer season. Diatoms species dominate in all sectors all year around.