Desalination plants provide a basic need to population, industry and agriculture. This seems sometime to evoke the impression that desalination plants are per se environmentally compatible. Even in fundamental texts environmental aspects are often missing. The objective of this paper is to analyse the imaginable environmental impacts of desalination plants on coastal zone ecosystems. We present a general frame for environmental impact studies derived from the experience gained from work on a distinct desalination plant. Among the impacts originating from a desalination plant are those restricted to the construction phase and those bound to the operation phase. Impacts start with the changed land-use, proceed to visual and acoustic disturbance and extent to the emissions to water and atmosphere and to the potential damages of the target environment. The extent of the damages depends on the sensitivity of the environment. After a discussion of the environmental, the chemical and the biological context, the emissions of desalination plants into the atmosphere and into the sea are examined. The potential hazards from these loads are discussed. At the side of the target environment, typical sub-ecosystems are selected and their sensitivity is assessed. Finally, sub-ecosystems are ranked according to sensitivity forming a scale ranging from a high-energy oceanic coast of low sensitivity to a mangrove coast of very high sensitivity.