Abstract. The Bistrita River Basin (a length of 283 km, a surface of 7039 km², a mean discharge of 65 m³/s) is one of the most important tributary of the Siret River, which is the second major affluent of the Danube River. Heavily influenced by hydraulic management and highly polluted by agricultural and urban activities in some stretches, the Bistrita river has been studied in the framework of the Diminish Project (LIFE03 ENV/ RO/000539), funded by the Life Environment Program. The project aims to support the implementation of the EU Water Framework Directive and to combat the nutrient pollution by developing an integrated, on-line, GIS-based support system for the management of the water quality in relation with human activities, using socio-economical analysis, at the scale of the river catchments. Based on modeling approaches the decisional system allows to predict which strategy will lead to the most effective reduction of nutrient concentrations within the Bistrita hydrological network and of nutrient loads transported by the Siret River into the Danube.

The consequences of the nutrient pollution are discussed for two basin areas, from two points of view: i) the effects of point and diffuse pollution for surface and groundwater, on the basis of the basin response to the changing pressures over the river catchments (industrial, rural, urban, agricultural changes), ii) the economical valuation of environmental costs and cost-effectiveness of the measures, that can be proposed from socio-economic scenarios, for reaching the "good ecological status" of this river.