The Orange river mouth is located on the arid Atlantic coast at South Africa’s border with Namibia. The nearest towns are Alexander Bay in South Africa and Oranjemund in Namibia. This site is a 13 km long section of the Orange river, including its flood-plain and terrestrial matrix, running from the ocean to Pachtvlei, just east of the Sir Ernest Oppenheimer Bridge. The delta-type river mouth consists of a series of braided troughs interspersed with sandbanks, channel bars and small islands, with a tidal basin and a saltmarsh on the south bank. The Orange river drains the largest catchment in South Africa, with an area of 549,700 km² and a mean annual run-off of 12,000 million cubic metres.The major vegetation-types include islands dominated by Scirpus, Phragmites and Sporobolus. The peripheral marshes are dominated by various herbs, sedges and grasses. The upper flood-plain vegetation consists primarily of Lycium, Tamarix and Juncus, which gradually give way to terrestrial vegetation. On the lower flood-plain the soils have a high salinity as a result of evaporation and the peripheral marshland is dominated by salt-tolerant Sarcocornia.
See Box and Table 3 for key species. The Orange river mouth is considered to be the sixth most important coastal wetland in southern Africa in terms of the overall number of wetland birds that it supports, which can be as high as 26,000 individuals, from a total of 56 such species recorded. Numbers drop off considerably in winter, suggesting that the large majority of the birds are migratory or indulge in local movements. The Orange river mouth is used by birds primarily for breeding or as a stop-over on migration. At times the area supports more than 1% of the world populations of Phalacrocorax capensis, Tadorna cana, Anas smithii and Larus hartlaubii. The wetland and adjacent coastal dunes also support substantial numbers of Sterna balaenarum. Substantial proportions of the southern African populations of Podiceps nigricollis, Oxyura maccoa, Charadrius pallidus, Sterna bergii, and Sterna caspia are periodically supported at the Orange river mouth. Circus ranivorus occur along marshy sections of the riverbank and in the surrounding lucerne fields. The mouth supports a few resident Haematopus moquini and, in summer, large numbers of migrant Palearctic waders.Near Pachtvlei, the terrestrial vegetation surrounding the wetland supports Francolinus capensis, Cercomela tractrac and two recently recognized larks, Certhilauda barlowi and C. curvirostris. The latter two species have restricted ranges (covering less than 50,000 km² each) that overlap, indicating that the Secondary Area of avian endemism recognized in this part of the Karoo (the restricted-range species Certhilauda burra occurs at three nearby IBAs: 025, 026, 027) should be upgraded to the status of Endemic Bird Area (EBA) when the global EBA classification is next revised.
Non-bird biodiversity: The system holds several endemic and threatened fish species, including Barbus hospes (LR/nt) and Austroglanis sclateri (DD). Several endemic and localized amphibians and reptiles occur in the terrestrial vegetation surrounding the estuary, and consideration should be given to securing a conservation area including the terrestrial matrix. Three highly range-restricted endemic frogs, Cacosternum namaquense, Breviceps macrops and B. namaquensis occur in the dunes and rocky outcrops adjacent to the mouth, particularly in the Alexkor restricted mining area to the south. Endemic mammals in the surrounding habitat matrix include Bathyergus janetta (LR/nt).
Pressure/threats to key biodiversity
After years of continuous habitat degradation as a result of several factors, including adjacent diamond-mining activities, flow regulation of the river and its catchment, and poor management of the mouth, the future is finally looking more positive for the Orange River Mouth Ramsar Site. The unprotected mouth (currently managed on an ad hoc basis by Alexkor, a diamond-mining company) and its saltmarsh are soon to be declared a provincial nature reserve and will be afforded the protection of a full-time nature conservator. A management plan will be developed, and rehabilitation options will be explored. A substantial proportion of the wetland falls within Namibia, where it is managed by Namdeb (Oranjemund), another diamond-mining company. Negotiations are currently under way to acquire the property for a trans-national conservation area. The southern African west coast is characterized by a lack of large, significant wetland systems. The Olifants river mouth (IBA 078), some 300 km south of the Orange, is the nearest wetland holding significant waterbird habitat. To the north, Walvis Bay (IBA NA013) lies c.700 km away. The Orange river mouth is thus of primary importance as one of the few major stop-over wetlands for migratory waders along the arid east Atlantic flyway, as well as being one of the few permanent wetlands for nomadic or moulting waterbirds.The Orange river system, South Africa’s largest, has become highly regulated by virtue of 23 major dams and numerous weirs within its catchment. Water abstraction and regulation have resulted in changed flow patterns, from a pronounced seasonal flow, primarily during summer, to a nearly even flow distribution. The total annual flow has also been reduced by half. To add to this, the functioning of the Orange river will be altered dramatically with the full implementation of the Lesotho Highlands Water Scheme. Worst-case scenarios project periodic drying up of the Orange river that would have extremely negative consequences for the functioning of the river system and its mouth. The saltmarsh on the south bank of the river has been degraded by a dyke, which was built to allow Alexkor personnel access to the beach. Furthermore, material from the Alexkor dumps has been blown across the saltmarsh, and through abrasion, clogging and other factors, has killed much of this vegetation. These anthropogenic impacts have resulted in the wetland having been placed on the Montreux Record (in September 1995), which is a register of sites administered by the Ramsar Bureau, that have suffered considerable detrimental action as a result of human activities. Alexkor have promised to rehabilitate the area and restore the saltmarsh, although it is unlikely that it will return to its former state.