The impact of humans on aquatic systems is covered in French high schools in the "Premiere" level (ages 16 to 17) by students studying economics and social sciences. We designed experiments to teach critical thinking about water pollution and how citizens can act to minimise it. The experimental session, which lasts three consecutive days, takes place in a non-profit public training centre for experimental science located within a research institute. The classroom is divided into groups of four to seven students, and each group is tutored by a PhD student. High school students are presented with results from publications on fish mutations, develop hypotheses, perform experiments and discuss their results, just as researchers do in their daily work. Students learn to ask and answer the following questions on the biological, chemical, economic and social aspects of water pollution: What are the origins of biological and chemical pollutants in an aquatic ecosystem? How can the population be made aware of aquatic pollution? How can the willingness of the local population to pay for the protection of their regional ecosystem be evaluated? At the end of the experimental session, each group of students prepares a poster presentation and discusses with an external expert. (Contains 6 figures, 3 tables, and 3 notes.)