We surveyed the River Rupel and River Durme, Flanders, between 10 and 13 April 2006. Both rivers aretransitional waters belonging to the Scheldt estuary. The Durme River is a tributary of the Scheldt River inFlanders. It is a relatively small tidal river. Dredging occurs in certain areas. The valley consists of generallylow-lying terrain, which is currently nearly entirely protected by dykes against the tides. The Rupel connects theRivers Nete, Dijle, Zenne, Demer and Gete with the River Scheldt. It is notorious for being heavily polluted.Fish assemblage data were obtained using fyke nets placed for a period of 24 hours. The nets were placed at lowtide, emptied the next day at low tide and removed. We surveyed three sites in each river using two fyke nets per site. Table 1 and the map in annex provide the co-ordinates of the sites.
Table 2 gives the methodology used.
Table 3 provides the descriptive information of the sampled sites and the abiotic variables (oxygen concentration, conductivity and water temperature) which were recorded during the survey.
Fish data include species, individual total length and weight. Table 4 gives an overview of the collected species according to the methodology used. Table 5 represents morphometric information of the species per location.
Table 6 presents the catch per unit effort per species.

In the River Rupel ten different species were collected. This is due to the incoming Scheldt water. In general the water quality is bad due to the River Zenne.
Although more species and specimens were collected in the River Durme, there were still less species than one would expect in a pristine water of this type. In total 12 species were collected.

In 2006 the purification of the River Zenne should lead to an increase of the water quality. This should have its effect on the River Rupel and the River Scheldt too. Further surveys will allow us to assess the trends in thesevery dynamic systems.
This report is a contribution to the European Interreg IIIb North Sea project Harbasins, aimed at harmonising European river basin management.