Verlorenvlei is a closed coastal estuarine-lake and marsh system of roughly 1700 ha, fed by an intermittent allogenic river. The estuary mouth lies along the Atlantic Ocean, 3 km east of Elands Bay and 25 km south of Lambert's Bay. Verlorenvlei is one of the largest natural wetlands along southern Africa's west coast, and it is one of the few coastal freshwater lakes in South Africa. The Verlorenvlei catchment covers some 1 890 km2 and consists of four main tributaries, the Kruis, Bergvallei, Hol and Krom Antonies rivers, which are primarily derived from the Olifantsrivierberge and Swartberge in the east and the Piketberge in the south. The four rivers drain the extensive flatlands of the sandy coastal plain and flow into the 30 km long Verlorenvlei River. Because of its intermittent connection with the ocean, Verlorenvlei can be regarded as a coastal lake and reed-swamp system. The lake is located north of a ridge of rugged hills with high cliffs near the sea. The main body of the lake is approximately 13.5 x 1.4 km with an average depth of 3 m and a maximum depth of approximately 4.5 m during the wet season. Extensive low-lying sand flats occur to the north and east of the lake, sloping up to a series of low hills that form the catchment boundary. On the southern side, the lake lies against the base of a continuous range of low sandstone hills averaging some 120 m a.s.l, with Muishoekberg (300 m a.s.l.) forming the only prom nent peak.
Verlorenvlei lies within a winter rainfall area; during winter it fills and overflows into the sea near Eland's Bay, but during summer it gradually desiccates, reaching its lowest levels at the end of the dry season. The fluctuations in water level influence wetland flora and fauna distribution patterns. The wetland's variable nature is therefore critical to the functioning of the system. Verlorenvlei is connected to the sea via a shallow, narrow, 2.5- km-long estuary channel, but a rocky sand-covered bar at the mouth and other artificial obstructions make Verlorenvlei a virtually closed system. The mouth is normally blocked and the channel is reduced to a series of stagnant saline pools. During good rains, the lake spills into the channel and some tidal exchange occurs. The lake is regarded as oligotrophic, but the nutrient status will vary depending on the water level. Salinity varies from 11.5 parts per thousand on the eastern side of the railway-bridge to 0.5 parts per thousand at Redelinghuys.
The terrestrial vegetation surrounding the vlei is transitional between karroid and fynbos vegetation, resulting in a high diversity of ecotonal communities. The coastal dunes support strandveld comprising clumps of succulent or evergreen shrubs which are interspersed with smaller shrubs and restios. Saline marshy areas with a dense cover of halophytic vegetation are found immediately inland of the seaward dunes and around the mouth of Verlorenvlei.
Birds
Verlorenvlei supports over 189 bird species; 75 are waterbirds. The wetland regularly supports over 5 000 birds and occasionally it holds over 20 000, including over a thousand waders of at least 11 different species. At least 26% of the Western Cape's Great White Pelican Pelecanus onocrotalus population occur at this site at times. Greater Flamingo Phoenicopterus ruber and Lesser Flamingo Phoeniconaias minor occur here when conditions at the nearby Rocher Pan (35 km south) or Wadrifsoutpan (13 km north) are unsuitable. Relatively large numbers of Little Bittern Ixobrychus minutus and Caspian Tern Hydroprogne caspia also occur regularly.
Most importantly, the area is a moulting ground and summer-refuge for Anatidae, and it regularly supports extremely large numbers of Yellow-billed Duck Anas undulata, Cape Shoveller Anas smithii and South African Shelduck Tadorna cana. Large numbers of Great Crested Grebe Podiceps cristatus, Red-knobbed Coot Fulica cristata, Hartlaub's Gull Larus hartlaubii and White-breasted Cormorant Phalacrocorax carbo are supported at this wetland. There is a high density of African Marsh Harrier Circus ranivorus, which forage over the marsh and reedbank areas. Black Stork Ciconia nigra, which breed in the nearby Olifantsrivierberge and Swartberge in the east and the Piketberge to the south, are often seen foraging in the vlei, which also holds 4–5 pairs of African Fish Eagle Haliaeetus vocifer.
African Black Oystercatcher Haematopus moquini and Chestnut-banded Plover Charadrius pallidus are recorded at the estuary mouth from time to time. The palustrine habitats are diverse and rich and hold populations of secretive rallidae including large numbers of Red-chested Flufftail Sarothrura rufa, African Rail Rallus caerulescens and Baillon's Crake Porzana pusilla. Rallidae are particularly abundant between Matjiesgoeddrif and Redelinghuys where the palustrine vegetation composition and structure are diverse and the area has extensive and excellent habitat for many rallid species and waders. The diverse ecotonal terrestrial vegetation around Verlorenvlei's fringes supports several restricted-range and biome-restricted assemblage species.