Prediction of conservation, instream, or environmental flow regimes is a challenging water resource management process. Fish habitats represent some of the most difficult biological, topographic and hydrodynamic phenomena to evaluate and simulate in detail. However, computational advances may now allow reasonable and accurate hydraulic and biological model results in such challenging circumstances. Numerical models, particularly 2-dimensional hydrodynamic models with habitat simulation features, provide one tool to examine aquatic habitats at various river flows to support management decisions. The purpose of this study was to evaluate the suitability of habitat throughout a range of flows by combining detailed hydraulic modeling with species-specific habitat suitability criteria that can be used to protect or enhance fish life in the Saskatchewan and Assiniboine Rivers, Canada. The two-dimensional finite element model, the RIVER2D (www.river2d.ca), was used to achieve these goals. Five reaches or study sites were investigated, three in the Assiniboine River, one in the North Saskatchewan River, and another in the South Saskatchewan River. The model was used to predict channel hydraulic characteristics, mainly discharges, velocities, depths and water levels. Model results for a wide range of discharges were presented. Model predictions were compared to detailed representative field measurements. The comparisons showed that the model performs reasonably well. The hydrodynamic results, coupled with biologically significant suitability metrics, were used to determine changes in fish habitat areas with discharge, and estimate weighted usable areas for several species. This ichthyohydraulic simulation process provides water management guidance.