Monitoring trace metals and hydrophobic substances in water is challenging. Therefore, chemical biomonitoring (i.e., monitoring contamination in biota) is often proposed as a relevant approach to characterize the contamination of aquatic systems. Active chemical biomonitoring (i.e., using transplanted organisms from a reference site) allows controlling exposure time, age and size of organisms, therefore providing comparable results. As such active approaches are still an emerging issue for continental waters, we recently implemented an active biomonitoring approach based on the ecologically relevant amphipod Gammarus fossarum. In a first study, Gammarids were translocated into cages to 27 sites in streams/river of the Rhône-Alpes basin. Study sites represented different physico-chemical characteristics and various anthropic pressures. To avoid the influence of biotic factors, only male with the same average body length were exposed and gammarids were fed during the experiment. After one week of exposure, concentrations of 11 metals/metalloids (Cd, Pb, Hg, Ni, Zn, Cr, Co, Cu, As, Se and Ag) and 38 hydrophobic organic substances (including PAHs, PCBs, PBDEs and organochlorine pesticides) were measured. All metals, except Ag, and 33 organic substances among 38 were quantified in G. fossarum, showing that this species is relevant for chemical biomonitoring. The control of biotic factors allowed a direct inter-site comparison of the bioavailable contamination levels. Overall, our results showed the interest and robustness of the proposed approach for assessing trends of bioavailable contamination in continental waters. Furthermore, we built threshold values of bioavailable contamination in gammarids, assuming that any concentration above such a threshold would be considered as representative of the bioavailable contamination at the sampling site. We will also present preliminary results on metals of a subsequent large-scale pilot study implemented in 2012 on more than 130 sites selected from across the French territory, to assess the validity at national scale of predetermined threshold values.