Thermal electric generating stations have a potential to alter the biotic and abiotic conditions in adjacent water bodies. Federal regulations require electrical utilities to monitor for such changes as insurance against deterioration of aquatic ecosystems. The cost of many monitoring efforts could be reduced by more precise applications of the scientific method (hypothesis testing), improved statistical design, and a focus on measures of cost-effectiveness. A multidisciplinary team of scientists and engineers from the University of Washington has developed such a conceptual framework to guide the design of power plant aquatic monitoring programs. This framework is organized into four hierarchical levels to accommodate the quality of information in a user's possession. Algorithms within the hierarchy help the monitoring program designer identify and prioritize mechanisms likely to cause ecological change, ecosystem components that might demonstrate a response, hypotheses of impact, and an appropriate sampling design for hypothesis testing. The entire framework has been programmed for interactive computer application.