The aim of the study is to determine effects of Izmir Big Channel Wastewater Treatment Plant on inorganic nutrients such as NO(3)(-)-N, NO(2)(-)-N, NH(4)(+)-N, PO(4)(-3)-P, Si and Chl-a levels in Izmir bay. Variations of inorganic nutrients and Chl-a were investigated weekly during 1 year period in 2003-2004 in Izmir bay. In addition, physico-chemical environmental parameters such as pH, Dissolved Oxygen (DO), water temperature and salinity were measured. The parameters mentioned above have been carried on in different depths of the 3 sampling stations which were located in middle and inner parts of Izmir bay. The concentration ranges of nutrients and chlorophyll-a were from BDL (Below Detection Limit) to 40.94 mu M for NH(4)(+)-N, BDL to 21.35 mu M for NO(3)(-)-N, BDL to 28.99 mu M for NO(2)(-)-N, BDL to 31.43 mu M for PO(4)(-3)-P, 0.16 to 54.12 mu M for Si and BDL to 66.13 mu g L(-1) for Chlorophyll-a. When the results were compared with those obtained before Izmir waste water treatment plant had been operated, concentrations of Chl a and nitrogen forms declined while it was not the case for PO(4)(-3)-P.