This proceedings publication reviews the present state of the art in applications of radioactive and stable isotopes in achieving a better understanding of environmental processes and in the protection of the aquatic environment. The main topics include: studies of the behaviour, transport and distribution of isotopes in the aquatic environment; climate change studies using isotopic records of the marine environment; global ocean isotopic studies; groundwater dynamics studies; submarine groundwater investigations; modelling of environmental processes; management of freshwater sources in coastal zones; new trends in radioecological investigations concentrating on the protection of marine biota against radioactive contamination; transfers in analytical technologies from bulk analyses to particle and compound specific analyses of environmental samples; development of new isotopic techniques such as ammonium molybdophosphate (AMP) and inductively coupled plasma methods (ICPMS); and their applications in environmental studies.