Due to their toxicity and their large-scale uses, pesticides are often pointed out as being among the main causes of the decline in biodiversity, and even of effects on human health. Monthly contamination by pesticides has been monitored continuously since 2008 in the Orgeval watershed. Pesticide concentrations are between 1 and 1000 ng.L-1 according to application periods. This is the case for S-metolachlor for which maximum contamination is observed in May-June. The Orgeval is thus a site of interest for the validation of new approaches to characterize contamination such as the use of passive samplers and to compare them with direct measurements (grab or integrated sampling). This work will allow us to find new strategies to determine effect markers on fish communities. Key points ✓ Monthly integrated sampling remains the best method to understand the contamination of small rivers by pesticides. ✓ Passive sampling is interesting of trace measurements but still requires calibration. ✓ Next studies will be conducted to measure biomarkers on fish.