The Zwin natural reserve, partly under Belgian and under Dutch management, is a relic of a former vast estuary. A breach in the eastern dunes forms the connection with the sea, and determines largely the value of the area. This breach forms a large trench, with several branches, feeding the Zwin plain with seawater. Some specific structures are present: the trench system and pools formed by human intervention, low and high salt marshes, low beaches and dune formations. Due to these differences in soil structure, hight, and water balance, there is a great diversity in the biotic properties of the the area, especially for the avifauna and the vegetation. The ecological potential and value of the area is high as a consequence of these circumstances. Several important management guidelines are explained, that need to be implemented to saveguard the important natural values of this area for future generations.