The paper describes the flow through a small water vortex turbine using the Ansys Fluent package. Before simulation and modelling, it was necessary to determine the location of the river that will be invested in the vortex turbine. The Krupa river near the Krupa monastery at the foot of Velebit was chosen as the location. The mean velocity of the river was measured using the floating method and the river flow was calculated based on this. We enter the model with the measurement values and they are set at the input. The shape of the model is designed so that it does not exceed the limits and possibilities of the original location. After the model has been designed, it starts with the simulation where the models are set as Multiphase and SST viscosity model. The model has 234,635 elements, and the number of nodes is 47,398. After the obtained results, optimization was performed with a change in the value of five input variables and one output variable, which was also the goal of the optimization. The optimization gave 3 candidates as the best result, and of those three candidates, the best candidate is number one whose output variable is 25% higher than the original model, which tells us that the optimization was successful. After that, the simulation of the turbine was carried out, with simple geometry where the range of angular speed from 1.05 rad/s to 21.05 rad/s was observed. After the simulation, the results for the torque and the degree of efficiency were obtained and are presented in diagrams.