In this study, a GIS-based Integrated Coastal Zone Management (ICZM) system which was designed and established for all stakeholders in the newly rehabilitated area, Halic (also known as Golden Horn) in the oldest part of Istanbul is introduced. The study also proposes enhancement methods in order to ensure the sustainability. Halic has experienced severe pollution until the recent years. This pollution of the Golden Horn and various proposals for amelioration had been the subject of much research and national policies ever since the 1960's. However, Halic cleaned up completely after a rehabilitation project was instigated by the Istanbul Metropolitan Municipality and Istanbul Water and Sewage Administration (ISKI). During the project and several others carried out later, enormous amounts of spatial and non-spatial data involving land and water were produced and used. The full efficiency of the produced data was not achieved, since data and systems were isolated. Hence, the main objective of this study is to establish a computer based information system for the area of Halic and its surroundings to integrate collected data in a spatial database for ICZM. The system includes several different kinds of data and information involving land and water environments such as census, topography, water quality, hydrology, bathymetry, infrastructure, documentation of cultural and historical values. The developed system is designed for managing these enormous amounts of data as well as sharing by the different level of users.