The seasonal development of phytoplankton biomass in the Nozha Hydrodrome during the period September, 1986- August, 1987 exhibited two annual peaks. The first in winter resulting from lack of nitrogen and availability of phosphorus, led to the development of N2-fixing alga Anabaenopsis circuiaris which averaged 11.50 and 9.14 mg.1'1 for the surface and near bottom layers respectively. The second peak in spring due to the diatom Cyclotella meneghiniana (10.9 and 11.0 mg.l"1 for the surface and near bottom layers, respectively). The annual averages phytoplankton biomass were 6.26 and 5.78 mg.l'1 for the two layers and lie within the range considered as characteristic of eutrophic waters. Small differences were found in the horizontal distribution and a slight increase was noticed from the western part of the hydrodrome to the east.Results indicate that the biomass of the different classes was altered when compared with its numerical values. While Chlorophyceae was numerically the most important plankter, Cyanophyceae constituted 51.4% of the total algal biomass.The multiple regression analysis between variations in phytoplankton biomass versus some physical and chemical parameters dealing with changes in its community illustrated excellent equations model which can be applied to predict the phytoplankton biomass in the hydrodrome.