Water resources management has shifted from flow regulation applications designed to protect public health to applications that include restoration of natural flow regimes and protection of aquatic ecosystems. The ecological flow regime uses a regime-based approach that considers hydrologic variability instead of focusing on identifying flows or flow targets for aquatic ecosystems. It determines environmental flow by embracing the multitude of species within an ecosystem rather than emphasizing a single species. In addition, the ecological flow regime recognizes that flow magnitude, duration, frequency, timing, and predictability must be incorporated into any flow management strategy. This paper provides a multi-objective approach to integrating ecosystem and human needs in water resources management. The ecological flow regime analysis provides a surrogate for ecosystem needs in analyzing the trade-offs with human water usage. The non-dominated sorting genetic algorithm (NSGA II) is used to find the Pareto set of operating rules for evaluation of reservoir operation for the Dahan River basin in Taiwan. It provides decision makers with the trade-offs between shortages in water available for human needs and ecological flow regime maintenance. Copyright ASCE 2005.