The next step is to look for the outlet of the catchment at the delineated stream and then calculate the catchment of this outlet.
1. Follow the delineated stream downstream to find the approximate location where the Rur (Roer in Dutch) enters the Meuse (Maas in Dutch) river. Use the OSM Standard and streams vector layer to find this location.
2. In the Processing Toolbox go to GRASS | Raster (r.*) | r.water.outlet.
3. In the r.water.outlet dialogue choose flowdirabs as Name of input raster map. For the Coordinates of outlet point click and choose the point on the delineated stream. Zoom in close enough.
4. Save the Basin as catchment.tif.
5. Click Run. Close the dialogue after processing.
6. Click right on the catchment layer in the Layers panel and choose Zoom to layer.