Biomass and Photosynthetic productivity of phytoplankton in relation to the physical andrnchemical conditions of the water column in Lake Kuriftu were studied from August, 2005rnto April 2006. All the physical, chemical and biological parameters measured variedrnspatially and temporally. The Lakeâ€™s transparency (ZSD) was always less than 0.6 m withrnsmaller values coincident with periods of rainfall and negatively correlated (r=-0.36)rnwith phytoplankton biomass. The chemistry of the lake was basically similar to the diluternEast African lake waters, with maximum pH and total alkalinity values of 8.8 and 3.1rnmeq/l respectively. The inorganic nutrients, which were of moderately high levels variedrntemporally as a function of hydrological, hydrographic and biological conditions of thernlake. The phytoplankton community which was consistently dominated by cyanobacteriarnexhibited low species diversity. Phytoplankton biomass measured as chlorophyll a variedrnfrom 18.35 to 45.18 mg Chl a m-3 at the near-shore station and from 17.24 to 55.6 mg Chlrna m-3 at the central station. The light-saturated rate of photosynthesis (Amax), which wasrnpositively and strongly correlated with phytoplankton biomass, ranged from 571 to 1136rnmg O2 m-3 h-1. Biomass-specific rate of photosynthetic productivity at light saturationrn(Pmax) ranged from 18.78 to 33 mg O2 (mg Chl a)-1h-1, while the hourly integralrnphotosynthetic production (Î£A) which was positively and strongly correlated withrnbiomass and Amax, varied between 0.686 and 1.05 g O2 m-2 h-1. The factors responsible forrnthe observed spatio-temporal variations in the physical,chemical and biological featuresrnof the lake are discussed.