Monitoring chemical pollution is a critical issue for the preservation of aquatic ecosystems and water quality. PFOS, a perfluorinated compound, highly persistent in the environment, is one of the highest-priority pollutants in the context of the WFD – Water Framework Directive – and must be monitored in aquatic environments, particularly in fish. Further to developing a methodology for monitoring contaminants in rivers focused on gammarids, small crustaceans sensitive to changes in their environment, the INRAE and the OFB have developed and tested an approach using these crustaceans to predict the contamination of fish. A feasibility study(1), published in ″Environmental Sciences Europe″, reveals that measuring the concentration of PFOS in captive gammarids accurately predicts that the environmental quality standard threshold of the compound has been exceeded.