The `snapshot' sampling methodology was applied to the spatial analysis of phosphorus and nitrogen concentrations and fluxes in the transnational upper Sûre watershed (Belgium–Luxembourg) during stable low discharge summer periods in 1991 and 1992. The results show clear differences in nitrogen concentrations and specific loads between agricultural and forested sub-basins, whereas for phosphorus the dependence on land use is less evident. The simultaneous measurement of stream discharge and nutrient concentrations permitted a quantitative evaluation of the input from point respectively diffuse sources and loads from the tributaries as well as the retention capacity by self-purification or sedimentation of the different phosphorus and nitrogen forms in the various sections of the Sûre river. The results illustrate the utility of the `snapshot' sampling as an important tool for an integrated watershed management.