This paper presents the use of evolutionary computation for simulating reservoir release rates that are central to developing hydrologic reservoir routing models for Lake Shelbyville and Carlyle Lake. The two lakes, which are located in the Kaskaskia River watershed in Illinois, are multipurpose reservoirs operated by the U.S. Army Corps of Engineers to meet flood control, water supply, navigation, recreation, and conservation needs. To date, the reservoir storages apportioned for water supply and navigation needs have not been fully utilized. The objective of the current study is to develop a model for examining the potential impacts of increased water supply and navigation uses on lake levels during severe drought conditions. The reservoirs have their own operating schedules that include ranges of seasonal release rates based on reservoir pool elevations. In this study, storage routing and multi-objective evolutionary algorithms were coupled to simulate reservoir release rates on weekly basis using long-term historical records of daily inflows, storages, reservoir pool elevations and outflows. The simulated weekly release rates for the two lakes complement their respective reservoir routing models and the modified reservoir routing models will ultimately be coupled with previously developed Kaskaskia River watershed model. The resulting coupled model will be able to provide simulations of storages and reservoir pool elevations for the two lakes under varying climate and water use conditions, in addition to simulating flows at different location in the Kaskaskia River watershed. The multi-bjective evolutionary algorithm used in this study was effective in simulating the reservoir release rates and its application was instrumental in developing the modified reservoir routing models for Lake Shelbyville and Carlyle Lake.