Current European water law inspires research, within which it is necessary to investigate numerous phenomena, with the aim to place responsible authorities in the conditions for the correct application of the norm. The attention is addressed mainly to the attainment of good water quality status, according to Water Framework Directive (WFD). This paper briefly presents a methodology used for implementation of watershed approach, with an aim of defining water quality in the lake’s immissary as a result of all different pollution-generating activities within the watershed. This paper describes therefore research lines of monitoring and modelling efforts to characterize nutrient loads in watershed scale. Following this integrated approach, it has been possible to identify satisfactory solutions to develop watershed project.