Intersex is the condition whereby both testicular and ovarian tissues are observed within the same gonad. The phenomenon traduces the exposure to endocrine-disrupting chemicals and can predict adverse reproductive effects for wild fish and populations. The occurence of intersex is documented in several aquatic ecosystem around the world but few data is available in French rivers. Also, due to the ecological relevance of this parameter, a large monitoring campaign is performed. For this purpose, wild Cyprinid fish were electrofished in rivers characterised by various levels of contamination and impact in fish population. Gonads were dissected and prepared for histological analysis. During microscopic observations, fish gender is noticed and sex-ratio is determined. For intersex fish, the ovotestis severity index previously developed in European flounder and recommended by OSPAR is calculated. Preliminary results of this large monitoring campaign will be presented. First results obtained in 13 sites show that intersex is observed in 8 rivers where 4 to 38% of fish are affected. To complete, two sites exposed to industrial presures, levels of occurence up to 50% are observed. Complementary works are in progress to analyse intersex occurence in other sampled sites (n=15) and to explore relationships between intersex and environmental pressures or fish assemblage quality.