Vertical slot fishways are hydraulic structures that enable fish to overcome obstructions in rivers. Depending on the target species for which the facility is intended, it is necessary to adapt the pool design to their needs. In order to do this, the first step should be to characterize the flow in the fishway. In this paper, the hydraulic characteristics of 16 designs of vertical slot fishways are studied using both a physical scale model and a numerical model which solves the depth averaged shallow water equations coupled with a k-ε turbulence model. A calibration or rating curve is developed for each design in terms of the dimensionless discharge and flow depth. Moreover, the water depth and velocity fields, and the circulation patterns in the pools are also studied. The experimental and numerical results are compared in order to validate the numerical model. The results provide useful information about how fishways can be modified in order to enhance fish passage. The agreement between the numerical and the experimental results suggests the possibility of using the numerical simulations as a complementary tool in the design of vertical slot fishways.