Phytoplankton assemblages and species succession along Lake Burullus (Southern Mediterranean) is expressed as carbon biomass (mg cm3) using a standard spreadsheet based on the species cell volume cell(-1) carbon relationship. High Chl a levels were measured (maximum 85-126 mg m(-3)) reflecting a dense phytoplankton population (up to 8.3 x 10(3) cell ml(-1) and 5.5 x 10(3) mg cm(-3)) throughout the lake body with maximum concentrations at the western sector of the lake (S1). Adiverse phytoplankton community was determined. Cell count data revealed the dominance of a mixed phytoplankton taxa, however biomass data indicates over-dominance of Bacillariophyceae (up to 98%). Good correlation (r = 0.73, p < 0.05) was found between Chl a and carbon biomass with various cell carbon/Chl a ratio according to variations in community structure. Bacillariophyceae were the most dominant, particularly at the middle (S2) and the western parts (S1) during periods of high nutrient (silicate) and good weather conditions (during spring/summer months). Chlorophyceae were abundant with Scenedesmus sp. mostly dominant, particularly at P-rich sites. Dinoflagellates peaked only during calm and high light summer months (May-July) being at a maximum level at S1. Euglenophyceae were less contributed to total phytoplankton abundance and peaked only; as a transition stage; at S1 during Jannuary and March (winter months). Cyanophyceae were numerous along with maximum peak at S2 affected by the southern drains. Excessive nutrient enrichment into the lake alters the existent structure of phytoplankton community. The water quality index indicated a poor water quality status of the lake.This may led to increase the possibility of toxic algal blooms to invade the lake ecosystem and, in turn, affect the lake fish yield.