River pollution models as an instrument for basin management

River models are considered a useful instrument in order to assess the effects of point and non-point loads on receiving river waters. The problem of load allocation and definition of wastewater treatment limit can be conducted on the basis of use of predictive models, by evaluating real verification of effects. The structure of models, the methodology for their validation and calibration are discussed, and the use of the obtained predictive tool is shown; applications are presented with reference to equilibrium between benefits from improved water quality, with lower externalities, and increased treatment cost. Also the problem of load reduction sharing between different subjects is presented, and attribution criteria are discussed.