• Summary
• Text account
• Data table and detailed info
• Map
• Reference and further resources

Site description
Situated c.80 km north of Richards Bay, Lake St Lucia is a subtropical coastal estuary with a long narrow channel to the sea. Located on the north-eastern KwaZulu-Natal coastal plain, the system is bounded by the Umfolozi river and its associated swamps in the south, and by the Mkuze river and Ozabeni in the north. The lake system is about 70 km long, and, excluding The Narrows, between 3 km and 18 km wide for most of its length. It is the largest estuarine system in Africa, with a water surface area that varies from 225–417 km². The mean depth is less than 1 m, and the water turbidity is high because the substrate is mainly fine silt. Hydrological conditions in the lake vary seasonally and in the long-term, with long periods of hypersalinity that result in large changes in the composition and abundance of plant, invertebrate and bird species.

Mangrove-fringed tidal banks extend into the estuary, where the mangroves Avicennia and Bruguiera are common, as is saltmarsh rush Juncus. Islands, estuarine mudflats and shallows are frequent. Aquatic vegetation (Potamogeton, Ruppia and Zostera) develops in the lake after prolonged periods of low salinity. Tall beds of reed and sedge, primarily Phragmites, Sporobolus, Scirpus, Cyperus and Typha, dominate the marginal vegetation. Surrounding these, above the water-table, are fringes of open vlei grassland. The grasslands and swamp flood seasonally, during longer-term wet cycles, to surround the patches of bush and forest on higher ground. The dry sand-forest around False Bay is never flooded, and dominants include Terminalia, Newtonia, Balanites, Dialium, Sclerocarya, Acacia and Strychnos. On the eastern shores, the coastal sand-dunes hold dune forest that runs parallel to the seashore in a band between one and three kilometres wide. The western shores hold the Dukuduku State Forest, a particularly dense and extensive patch of coastal forest, with trees of Trema, Ficus, Albizia and Ekebergia. There are also freshwater pans, vleis, reedbeds and sedge swamps. Extensive pine Pinus plantations occur around much of the estuary.

To the north of St Lucia, the Mkuze river, which forms the northern and eastern borders of Mkuzi Game Reserve (IBA ZA043), forms a massive wetland complex after it leaves the reserve, before it drains into the northern portion of Lake St Lucia. It contains large beds of reed Phragmites and papyrus Cyperus, marsh with sedges and grass, nutrient-rich pans with good floating, fringing and emergent vegetation, swamp-forest of Ficus, Voacanga, Ilex, Urera and Syzygium, and dense, short coastal grassland (interspersed with muddy creeks and narrow channels). To the north of the main swamp are Muzi, Mpempe and Mdlanzi pans, which are long, narrow cut-off lakes with predominantly bare shorelines. Tall woodland or thicket surrounds these pans where the water-table permits. Further east, in the Ozabeni area, the soil becomes progressively more sandy, and open grassland dominates. Surrounding the marginal vegetation are fringes of open vlei grassland. Apart from isolated clumps, the only real forest in this area is a broad strip of swamp-forest associated with the Mbazwane Stream. The whole Mkuze Swamps and Ozabeni area holds a very diverse mosaic of wetland vegetation and appears to be largely undisturbed.

Key biodiversity
See Box and Tables 2 and 3 for key species. The St Lucia system supports over 350 bird species and is the most important breeding area for waterbirds in South Africa, with at least 48 breeding species recorded. Owing to its subtropical position, several bird species reach the southern limits of their ranges at St Lucia. Owing to the variability of the system, the lake may often hold very important numbers of a species in some years and almost insignificant numbers in others. At times, Lake St Lucia holds extremely large numbers of Pelecanus rufescens, P. onocrotalus, Platalea alba, Anas smithii, A. undulata, Recurvirostra avosetta and Phoenicopterus minor. Phoenicopterus ruber bred here in 1972, when some 30,000 birds and 6,000 nests were recorded owing to an increase in food, produced by a period of low salinity that followed a long hyper-saline period. St Lucia also holds the only breeding population of Ephippiorhynchus senegalensis in KwaZulu-Natal and is one of only three breeding sites for Mycteria ibis in KwaZulu-Natal. The lake can hold over 80% of South Africa’s breeding population of Sterna caspia. The colony of Pelecanus onocrotalus is the only known breeding colony in south-east Africa. Large numbers of Palearctic migrant waders occur in summer.

Forests on the eastern shores of Lake St Lucia hold Circaetus fasciolatus. In winter the coastal forest also holds small numbers of the globally threatened Zoothera guttata. In wet years, the flooded grassland between St Lucia and Cape Vidal supports Macronyx ameliae. Three restricted-range species are common here—Apalis ruddi, Nectarinia neergaardi (100–150 breeding pairs) and Hypargos margaritatus—and all occur in sand-forest thickets surrounding the lake.

The Mkuze swamps and Ozabeni areas are less well known. However, the area is thought to be excellent for waterbirds, particularly rails (Rallidae). Swampy backwaters with overhanging vegetation are home to Gorsachius leuconotus, Podica senegalensis and Scotopelia peli. The open flood-plain and flooded grasslands with dunes hold Anthus brachyurus, Turnix hottentotta, Caprimulgus natalensis, Centropus grillii and Macronyx ameliae. Although seldom recorded, Botaurus stellaris almost certainly occurs widely in the very extensive reedbeds.

Non-bird biodiversity: As befits a World Heritage Site, St Lucia has a wealth of Red Data and endemic species. Endemic to the IBA are the plants Kalanchoe luciae, Rhus kwazuluana and a new species of Aloe, and five species of butterfly. The mammal Diceros bicornis (CR) has been reintroduced.

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Recommended citation
BirdLife International (2020) Important Bird Areas factsheet: Lake St Lucia and Mkuze Swamps. Downloaded from http://www.birdlife.org on 31/10/2020.