ESWAT--Extended Soil and Water Assessment Tool--was developed to allow for an integral modelling of the water quantity and quality processes in river basins. The diffuse pollution sources are assessed by considering crop and soil processes and--together with the point sources--further transformed by an in-stream water quality module. An autocalibration procedure allows for the optimisation of the process parameters. The optimisation uses a global optimisation criterion, whereby several objective functions can be considered or combined and whereby several output variables can be taken into account simultaneously. The model and the calibration procedure are applied to the river Dender in Belgium.