In the 12th century, a storm broke through the dunes of the Flemish coast. It formed a tidal channel that reached as far as Bruges. Due to the silting of the channel, now all that remains are a saltmarsh, mudflats and brackish pools. A creek connects nature reserve Het Zwin to the North Sea. The reserve on the Belgian-Dutch border is an important area for roosting, wintering and breeding water birds. In 1986 the site was declared a Ramsar site.