The Site is a 40-kilometre long area of intertidal waters with mudflats. The former Oosterschelde en Markiezaat Ramsar Site was in 2014 divided into two Ramsar Sites, the larger Oosterschelde and the smaller Markiezaat (Site no.2211), following Natura 2000 boundaries. This led to an increase in their combined area of 810 hectares. Oosterschelde is an important component of the West Paleartic Flyway, with international importance due to the wintering, staging and breeding of a large number of waterbirds. The Site supports threatened birds such as the sandwich tern (Thalasseus sandvicensis) and pied avocet (Recurvirostra avosetta). It is an important spawning ground for many fish including garpike (Belone belone), sole (Solea solea) and plaice (Pleuronectes platessa). Aquatic mammals such as the harbour porpoise (Phocoena phocoena) and harbour seal (Phoca vitulina) regularly use the Site. The marshland plays an important role in flood mitigation. Human activities are related to tourism and the fishing and shellfish industries. Potential threats to the ecological character of this wetland include the disturbance of birds by these activities and a reduction in the tidal volume and flow caused by the construction of dykes, dams and other barriers.