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Site description
This reserve lies between Tableview and Milnerton in the northern sector of the Greater Cape Town Metropolitan Area, 10–15 km north-east of the city centre. A range of natural and semi-natural habitats exists in this fluctuating wetland, which floods in winter and dries out in summer when the estuary mouth closes. These habitats include shallow marine waters, estuarine waters, sand/shingle shores, tidal mudflats, saltmarshes, coastal brackish saline lagoons, rivers, streams and creeks, permanent freshwater lakes and permanent and seasonal freshwater marshes and pools.

Five distinctive wetland plant communities occur: perennial wetland, reed-marsh, sedge-marsh, open pans and sedge pans. The perennial wetland is characterized by scant aquatic vegetation, dominated by Ruppia, Potamogeton and Enteromorpha. The reed-marsh is dominated by Phragmites, invaded in places by Typha. The sedge-marsh is dominated by Bolboschoenus and Juncus. The open pans are sparsely covered in macrophytes, consisting mainly of Limosella and Salicornia, and the sedge pans are dominated by Bolboschoenus in summer and Aponogeton and Spiloxene in winter. Zooplankton multiply rapidly after winter flooding and disappear in summer as the water dries up. In the estuary there is a range of salinities, resulting in a diverse community of zooplankton. The invertebrate fauna is a vital food source for birds and fish, the most abundant fish in the wetland being Liza richardsoni.

Key biodiversity
See Box for key species. A total of 173 species have been recorded at Rietvlei, of which 102 are waterbirds and 76 are present regularly. Breeding has been confirmed for 23 waterbird species and is suspected for a further 13 species. The high diversity of waterbirds is due to the wide range of wetland habitats present and the proximity of Rietvlei to the ocean, which allows both freshwater and coastal species to exploit the system. Fluctuating water-levels are intrinsic to Rietvlei’s biological value. During peak floods, swimming birds of deep, open water abound. Birds of marshy habitats replace these as the water recedes, and waders exploiting shallow mudflats occur in great abundance just prior to the wetland drying up. Rietvlei has been ranked as the sixth most important coastal wetland in South Africa for waterbirds, and it supports an average of 5,550 birds in summer; during good years, however, numbers are boosted above 15,000. Phoenicopterus minor, a species of global conservation concern, occurs at the site, but not in globally significant numbers.

Non-bird biodiversity: Urban development and encroachment by non-native plants threaten the herptiles Cacosternum capense (LR/nt), Hyperolius horstockii, Bradypodion pumilum (CR) and B. occidentale, which all live on the wetland fringes.

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Recommended citation
BirdLife International (2020) Important Bird Areas factsheet: Rietvlei Wetland: Table Bay Nature Reserve. Downloaded from http://www.birdlife.org on 03/12/2020.