The distribution and transport of total suspended solids (TSS) is considered in order to propose the strategy which, when implemented, would lead to compliance with the water quality criterion. Currently, most of the water in Izmit bay has a TSS concentration in excess of the legal maximum of 30 mg/L TSS. Modelling and simulation shows that the majority of the TSS does not originate from the known land based sources but probably represents phytoplankton. Since excessive quantities of N and P are discharged into the bay, sometimes the growth of phytoplankton is limited by the natural silicate content of the water. However, it is found that most of the phosphorus discharged from land based sources is in fact utilized by the phytoplankton. Hence, reduction of the TSS concentration to the legal limit can be achieved by decreasing phosphorus sources. If the majority of total organic carbon emanating from land based sources were removed, this would imply a considerable decrease in phosphorus inflow. It is suggested that waste waters from residential communities and the remaining industry should be treated and released to the layer below the halocline using one outfall in the eastern part and one or several outfalls in the central part of the bay
