Warm discharges from industrial processes have the potential to impact benthic invertebrate communities and undermine river functioning as well as inform climate change impacts. We evaluated the effects of heated cooling waters from 2 power plants across 2 River Shannon locations (Ireland) in summer and in winter. The overall multivariate community composition differed significantly between heated and unheated river sections in both seasons. In summer, overall invertebrate taxon richness and diversity were significantly lower in heated than in unheated sections. This finding was coupled with a striking decrease in Ephemeroptera, Plecoptera, and Trichoptera (EPT) abundance, taxon richness, and diversity in heated sections. Furthermore, aerial taxon richness and diversity were significantly lower in the heated sections. We also observed that the abundance of grazers was lower in heated sections. Winter patterns were similar to summer, but with lower invertebrate community abundance and decreased functional representation of shredders, gatherers, and predators in heated sections. Such impacts likely have strong implications for river functioning, including depressed connectivity with riparian habitats, and may impair the performance of eutrophication biomonitoring tools that rely on EPT taxa. Our results highlight the impact of warming of thermal plumes and other ubiquitous triggers of heating and may indicate climate change-driven trajectories.