This study deals with the Environmental Impact Assessment (EIA), which is a systematic identification and evaluation of the potential impact of a proposed project or any action that may affect of the environment directly or indirectly in temporary or permanent terms, of off shore oil spill on desalination plants. Sources of off shore oil spill, fates and effects on different environmental items are discussed. The setting conditions and ecological life around Umm Al Nar desalination station, Abu Dhabi, UAE, are discussed. A hypothetic case of oil spill is assumed around the desalination station and the hydrodynamic model was used to predict the direction and concentration of oil around the station with emphasis on the places where seawater was used as feed water to the station. Based on predicted concentrations, the EIA was evaluated via the Rapid Impact Assessment Matrix (RIAM) model. The RIAM model seeks to overcome the problems of recording subjective judgments by defining the criteria and scales against which these judgments are to be made and by placing the results in a simple matrix that allows for permanent records of the arguments in the judgment process. In the EIA, the influence of oil contaminated seawater, when it is used as the feed water to the desalination plant, on the performance of system equipments and production water has been discussed. System units such as heat transfer tubes, temperature control, brine heater, vacuum system and evaporation chamber were utilized for evaluating the system performance. Production water quality was evaluated in relation to chlorination and organo-halogenic compounds, formation of trihalomethane (THM) by chlorination of product water, and corrosion of plant materials. Various remedial measures were proposed and evaluated in view of their technical, environmental (physical, chemical and biological), social and economic aspects.