The simulations with the model MACH3 yield knowledge about spreading of pollutants and about exchange rates as it never could be achieved by any scattered measurements. The persistance and transport of matters discharged by rivers, atmosphere, scattered sources, ship accidents, and by dumping can be determined area-covering and three-dimensional. Scenario-computations yield exact informations about the distribution of substances dependent on the actual and mean meteorological and waters-specific conditions. Thus, polluted areas can be detected and sustainable measures for improving the water quality of these polluted areas can be assessed and can be optimized.