Verlorenvlei is one of the most important estuarine systems in the Western Cape and one of the largest natural wetlands along the west coast of South Africa. It is also one of the few coastal fresh water lakes in the country. The system comprises a coastal lake and reedswamp connected to the sea by a small estuary. Situated amid dramatic topography, the lake is approximately 13.5 km long and 1.4 km wide and occurs in the zone of transition between the karroid and fynbos vegetation types. This results in the region displaying a high species diversity typical of an ecotone area. Rare plants that have been recorded from this area include Ferraria foliosa, F. densepunctulata, Cerycium venoum (presumed extinct) and Cullumia floccosa.

The wetland is regarded as one of the ten most important wetlands for wading birds in the south-western Cape, being a particularly important feeding area for the white pelican Pelecanus onocrotalus and supporting a number of threatened bird species. It supports over one thousand waders of more than eleven different species, mainly migrants from the northern hemisphere and provides further feeding, nesting and resting facilities to over 75 other species. The lake is a type locality for several species, including the whitebacked duck Thalassomis leuconotus. The only indigenous freshwater fish species occurring in the lake are the Cape galaxia Galaxias zebratus and the rare Barus burgi. Certain rare and threatened mammals such as Cape clawless otter Anonyx capensis have been recorded in the area.