Polychlorinated biphenyls (PCBs) are a family of synthetic chemicals consisting of carbon, hydrogen, and chlorine atoms. PCBs have been produced commercially since 1929 in hundreds of industrial applications. Their continued production in the United States was phased out in the late 1970s, and strict disposal guidelines were regulated as adverse health effects associated with exposure to PCBs was discovered. PCB contamination is still prevalent in many areas of the country, including the Ohio River basin. The Environmental Protection Agency (EPA) regularly monitors for the presence of PCBs in the environment. The primary health risk to humans associated with some PCB-contaminated sites, such as the Hudson River, is through eating contaminated fish. As such, a common method for monitoring an environment for PCB contamination is to analyze fish. This article shares an experiment intended to mimic the monitoring of fish samples collected from a watershed suspected to contain a source of PCB contamination. Students use a fictional map of a watershed along with small samples of fish fillets to screen for the presence of contamination. At the end of the experiment, the entire class pools their results to draw conclusions. This lesson uses active, collaborative, inquiry-based learning techniques that help students become more engaged learners.