The tidal tloodplain of the Zwin between Knokke (Belgium,Flanders) and Cadzand(Netherlands) is a border-crossing relic of the sound that once connected the medieval ports of Damme and Sluis with the North Sea and gave Bruges its golden age. Historic land reclaim, that only ended in 1872, reduced the Zwin to a tidal lagoon with a superficies of only 200 hectares, comprising salt marshes, mudtlats, tidal gullies and coastal dunes. Once an important sanctuary for coastal bird-species, the Zwin is in both concerned European Union member states included in the European Natura 2000 network. Since the years 1980, accelerated silting up of the lagoon and gullies and encroachment of the salt marshes with Elymus athericus have resulted into a significant loss of biodiversity. The accelerated silting up is caused by the lack of dynamics in relation to the too small scale of the remaining sea-inlet. After the necessary hydrodynamic modelling and an Environmental Impact Assessment were carried out, it was decided that the tloodplain of the Zwin should be enlarged with 120 hectares by moving the searetaining dike inland. The Agency for Nature and Forest (Flanders) has, together with the Province of Zeeland (Netherlands), also elaborated an arrangement-plan for the presently existing tidal site. This arrangement-plan prescribes rejuvenation of the salt marshes by cutting off sods and grazing by cattle and livestock as well as restoration of a tidal lagoon and expansion of the main sea-inlet by excavations.