Since recent decades, nutrient-related eutrophication, originating from agricultural use of fertilizer and population enhancement, can be considered worldwide as the main disturbance for coastal lagoons. Since coastal lagoons are very shallow and enclosed, their functioning is tightly linked to meteorological conditions. The aim of this study is to compare different rainfall levels and eutrophication response on coastal lagoons of the Languedoc-Roussillon (Western Mediterranean coast), subject to different nutrient loads from their watershed, in order to check the possibility to distinguish the effects of watershed management or rainfall conditions on water quality (waste water treatment plant improvement, decrease of fertilizer spreading).