This project's objective was to control the pollution of Izmir Bay. It consists of a Main Pipeline, Main and Secondary Collectors, Pump Stations, a Separate Sewage System, Water Intake Structures from the River and a Wastewater Treatment Plant. Project flowrate of the plant is 7 m3/s and 2/3 of the total capacity has been completed. Gùzelbahce Wastewater Treatment Plant, another part of the project, will treat the wastewater of the Southwest part of the lzmir City. It has signed a contract and they must finish it in a year. Revision studies were also done on the sewage collection system. lzmir Sewage System and Cigli Wastewater Treatment Plants are introduced in detail, and some structures to be built are described. Environmental impacts of treatment plants on lzmir Bay and the surrounding region and usage of treatment plant effluent for some useful purposes like irrigation and process water are also discussed.