The Ocean Thermal Energy Conversion (OTEC) is a marine renewable energy system that uses the temperature difference between the cold deep waters and warm surface waters to produce electricity. DCNS, a world-expert in naval defence and an innovator in energy has conducted technical, juridical and environmental feasibility studies of a plant offshore Martinique under an agreement with the Regional Council. In this context, DCNS realised a preliminary Environmental Impact Assessment in order to prepare public debate to be done further. Due to innovation of such a project, a specific methodology has been done for that. First step was to study bibliography in details, for site assessment of course, but also for impacts of other projects in the world that should present relevant similarities with OTEC (coastal thermal power plants for example). This bibliographic study dealt with thematic synthesis for each topic of physical, biological and human field that could be impacted by the project (total of 28 topics). The aim was to define priorities for specific assessments that have been done further: acoustic impacts, biogeochemical impacts of artificial upwelling, biofouling impacts, etc. Some of these topics are now on course with specific scientific research programs that have been launched at the end of this study. For each new topic, a specific methodology has been used or adapted for OTEC. These methods are made step by step, with a preliminary approach followed by a specific research program when it is necessary. Noise prediction has been done with a specific tool used for ship construction industry and a 3D propagation modelling. Biofouling has been assessed by a bibliographic approach and will be précised further with experimental moorings. Biogeochemical and biological impacts due to artificial and localised upwelling are now being studied in details with a double skill approach (physical modelling and plankton analysis), after preliminary water chemicals' analysis and modelling.