<p>Thermal discharges from nuclear power plants (NPPs) pose an important environmental challenge. Elevated effluent temperatures affect aquatic ecosystems and alter chemical processes and accelerate reaction kinetics and reduce dissolved oxygen levels. These effects also alter pollutant solubility and toxicity, and disrupt nutrient cycling—favoring thermophilic species and suppressing sensitive taxa. This review synthesizes current knowledge on the thermal impacts of NPP effluents, with emphasis on their influence on chemical equilibria and pollutant dynamics. A literature-based approach was employed, integrating chemical risk assessment (CRA) with mechanistic frameworks such as adverse outcome pathways to evaluate the combined effects of thermal and chemical stressors. The findings highlight that thermal discharges undermine the self-purification capacity of aquatic systems, increase the risk of eutrophication, and contribute to ecosystem destabilization. Mitigation requires not only regulatory enforcement and the adoption of advanced cooling technologies but also the refinement of CRA models to account for temperature variability, climate interactions, and salinity gradients. These measures are essential for reconciling sustainable energy production with the protection of aquatic biodiversity.</p> Graphical abstract <p></p>