Eutrophication has become an important environmental problem in coastal waters and its effects have increased due to the inflow of organic compounds and nutrients as well as the alterations in nutrient ratios. Besides the impact of streams, Izmir Bay, particularly the inner part of the bay, receives mainly continous domestic and industrial inputs of phosphate. Occasionally, these inputs can reach extreme levels. Consequently continous phosphorus enrichment has been occurring. Nevertheless, the fate of phosphate its effect on the phytoplankton biomass and the species dominancy in this biomass are poorly known. The seasonal patterns of phosphate, chlorophyll-a and abundance distributions of phytoplankton were determined in Izmir Bay between 1993 and 1994 in order to document the relationship between phosphate and phytoplankton. In spring, the increase in phytoplankton abundance associated with the phosphate decline suggested that the phosphorus uptake by phytoplankton was a major process responsible for the phosphate removal. It seemed that the bulk of inorganic phosphate in summer i.e. June 94, results from the resuspended anthropogenic sediment load in the water column in the inner part of the bay, which is a semi-enclosed coastal basin. Owing to inadequate light conditions caused by high turbidity in this basin, it was assumed that the high amount of phosphate could not be recycled, but rather transported to the middle part of the bay where it enhanced the formation of phytoplankton bloom.