The first seven years after closing off the area, Lake Grevelingen was completely cut off from the North Sea. The salt water slowly turned into fresh water due to rain and an influx of water from polder pumping station. Damming the area was a huge change for the nature in the Grevelingen, which meant that some plants and animals dependent on a saltwater environment disappeared. New areas of dry land where the rain washed the salt out of the soil experienced a large-scale disappearance of plants that need a saltwater environment to live, such as sea blite, sea lavender, glasswort and the sea aster.
Pioneer plants then appeared on the bare ground, which ripened the soil and filled it with nutrients. After a while, other plants also established themselves, such as plants found in wet dune valleys like centaury, grass of Parnassus and yellow wort. Dense thickets mainly of sea buckthorn are found particularly in the dryer areas at a higher elevation.
To prevent the entire area from being overgrown, various locations such as the south part of Slikken van Flakkee and the natural islands of Hompelvoet, Dwars in de Weg, Veermansplaat and Stampersplaat have cows and horses that graze there, and certain areas are mowed on a regular basis. These open areas often feature exceptional plants, such as several kinds of orchids.
Southern marsh orchid