De Hoop Vlei is situated within the De Hoop Nature Reserve, 65 km from Bredasdorp in the Western Cape Province. The wetland is partly located in a picturesque gorge with high limestone cliffs, and consists of a coastal lake 16 km long, formed where the mouth of the Sout River is blocked by coastal dunes. The lack of a visible outlet to the sea, and widely fluctuating salinities make this system unique within the south-western Cape.

The wetland is highly productive, with 75 wetland-dependent bird species having been recorded in the area, many of which are found in large numbers. Significant populations of yellowbilled duck Anas undulata, representing 7.1% of the South African population, are found, along with 15% of the world population of Cape shoveller Anas smithii. Both of these species are known to breed in the vlei. The wetland is also well known as one of very few South African breeding sites of the greater flamingo Phoenicopterus ruber. Other bird species such as the white pelican Pelecanus onocrotalus, black stork Ciconia nigra, lesser flamingo Phoenicopterus minor, Caspian tern Hydroprogne caspia, little bittern lxobrychus minutus and chestnutbanded plover Charadrius pallidus also make use of the wetland habitats.