This freshwater lake used to be a brackish estuary in the Rhine and Maas (Meuse) delta but was separated from the North Sea in 1970 by the Haringvliet dam. In 2014 the Site was aligned with the Natura 2000 site, resulting in an increase in its area of 74 hectares. Hollands Diep is an especially important area for breeding waterbirds such as the Eurasian spoonbill (Platalea leucorodia) and barnacle goose (Branta leucopsis), and a valuable spawning, nursery and feeding ground for national threatened fish species such as barbel (Barbus barbus) and other migratory fish including silver salmon (Salmo salar). The Site plays an important role in flood regulation and sediment trapping. The lake and the adjacent land are used for forestry, farming, commercial fishing, shipping, water management, conservation and research. Factors adversely affecting the Site’s ecological character include industrialization, urbanization and pollution leading to eutrophication.