A screening ecological risk assessment was performed for regulatory compliance at two Ontario nuclear power generation station sites to establish design requirements for a contaminant-monitoring program and to address the need for non-contaminant stressor management. Site-specific assessments went beyond traditional contaminant risk assessment to include stressors associated with land-use change, cooling water systems and site storm water runoff. Valued terrestrial and aquatic ecosystem components were selected from species lists after stakeholder consultation, and contaminants of concern were selected based on their relative loadings, and with respect to regulatory and literature-based benchmarks. Predictive modeling was used to estimate chemical and radionuclide exposures and likelihood of effects. Potential adverse effects on biota were predicted for aqueous emissions of chlorine and storm water but not for radionuclides. Retrospective analyses of field monitoring were used to determine likelihood of effects from non-contaminant stressors. Individual-level adverse effects were observed for fish losses from cooling water intake. Depending on the site and the biological species, either beneficial or adverse effects from thermal discharge were observed. Follow-up studies include monitoring, laboratory study, computer modeling and mitigation. Field monitoring will generate more precise species-level estimates of intake fish losses, magnitude of fish response to thermal discharge and chlorine concentrations in near-field discharge waters. Laboratory study is determining the effectiveness of intake fish loss mitigation technology. Computer fish population models are being used to design field studies and interpret individual-level effects. Mitigation includes storm water controls and habitat biodiversity management projects to offset past losses from site development and construction. Contaminant monitoring is planned to collect necessary information to verify site specific risk assessment model predictions and confirm model parameters and assumptions. The updated contaminant risk assessment models will be used to adjust site monitoring programs.