Summary The Nyl River forms a 70 km long, 16 000 ha grass floodplain, one of the largest in South Africa. It runs from 10 km south of Mookgopong north to Mokopane. This is the largest wetland of its kind in South Africa and it is basically a grass-dominated, seasonally inundated floodplain which can hold thousands of waterbirds.
Site description The Nyl river forms a 70-km-long grassland flood-plain, one of the largest in South Africa. It runs from 10 km south of Naboomspruit north to Potgietersrus. The area, known as Nylsvley, is located in extensive undulating to flat terrain between 1,050 and 1,080 m. The flood-plain starts to widen at the western edge of Nylsvley Nature Reserve and it attains its greatest width, of five to six kilometres, on the farms downstream from there: Vogelfontein, Weltevreden, Zyferkraal, Du Toits Kraal (the last three embraced by the Mosdene Private Nature Reserve), Groenvaley and Zandpan. At its northern end, on the farm Vaalkop, it narrows and assumes the character of a normal river. The only prominent hills occur at Maroelakop (1,140 m) and Stemmerskop (1,090 m), both are on Nylsvley Nature Reserve and are in close proximity to each other. The system derives its floodwaters from rain that falls in the nearby foothills of the Waterberg range (IBA ZA006).This is the largest wetland of its kind in South Africa and it is basically a grass-dominated, seasonally inundated flood-plain, which in years of poor rainfall may not be flooded at all. It requires rainfall of at least 10% above the annual mean to produce significant inundation. The dominant grass in flooded areas is Oryza longistaminata, which may grow up to 2 m tall and provides cover, food and nesting material for many wetland birds. Many other grass species occur. Dominant sedges include Cyperus, Schoenoplectus and Eleocharis. Large stands of reed Phragmites are also found.Bushes and trees, many of Acacia, are scattered throughout the flood-plain and provide nesting sites for herons, bitterns and egrets. On some of the high-lying areas the vegetation comprises broadleaved savanna and grassland, with trees (up to 9 m tall) of Acacia, Burkea, Terminalia and Combretum. The well-drained low termitaria support Acacia thickets.
Key Biodiversity See Box for key species. The area has a list of 426 bird species, about 46% of the species found in southern Africa. The flood-plain occasionally erupts with activity, holding up to 80,000 birds during high rainfall years. Egretta vinaceigula, Ardeola rufiventris, Sarothrura boehmi and Porzana pusilla breed erratically, whenever conditions are suitable. A relatively large Crex crex population occurs here in the austral summer. The wetland also occasionally supports extremely large numbers of Casmerodius albus, Ardeola ralloides, Nycticorax nycticorax, Platalea alba and Netta erythrophthalma. Tyto capensis is fairly common in the flooded grasslands and Glareola nordmanni occasionally occur in large numbers in the drier grassland surrounding the flood-plain. Almost every species of South African duck is found here from time to time, some in very large numbers. The surrounding woodland holds several restricted-range and biome-restricted species.
Non-bird biodiversity: The reserve holds the mammal Hyaena brunnea (LR/nt).