The Site is a stagnant freshwater lake with submerged vegetation in the catchment of the river Rhine, which was separated from IJsselmeer by the closing of Houtribdijk in 1976. The two separate Ramsar Sites “Ijmeer” and “Markermeer” were merged into a single Site and aligned with the Natura 2000 boundary, increasing the total measured area by 131 hectares. The Site is of international importance for a large number of breeding and non-breeding birds, supporting regularly more than 20,000 wintering waterbirds, including protected species such as the gadwall (Anas strepera) and the Eurasian Wigeon (Anas penelope). Large resting groups of common pochard (Aythya ferina), tufted duck (Aythya fuligula) and Eurasian coot (Fulica atra) gather in relatively small areas. The lake is also an important spawning, nursery and feeding ground for fish and molluscs, and plays an important role as a freshwater reservoir for irrigation. Human activities include boating, tourism, extractive operations, commercial fisheries, shipping traffic, water management, conservation and research. A large-scale restoration project is currently being undertaken, the Marker Wadden project, in which sand, clay and silt from the Markermeer are being used to create an archipelago of 10,000 ha in total.