This interrupted case study is based on a journal article that describes the rapid adaptation of a population (in this case, steelhead trout) in response to a shift in environmental conditions despite genome‐wide reductions in genetic diversity. First, students learn the basics of natural selection and explicitly link phenotype to fitness as well as fitness to changes in genotype. The discussion then shifts to the evolution of steelhead trout as a result of relocation from salt to freshwater. Students develop hypotheses of expected genomic changes and cultivate skills in interpreting genomic data. The case focuses primarily on population response to changes in habitat, and as such is appropriate for a class focused on response to local habitat changes (e.g., salinity changes in aquatic systems). The case is designed for evolution, ecology, or genomics courses primarily comprised of biology (or related discipline) majors.