Lake St. Lucia

Lake St Lucia, also known as Lake Saint Lucia, is an estuarine lake system in northern KwaZulu-Natal, South Africa. Spanning roughly 325 to 350 square kilometers, it is the largest estuarine lake in both Africa and Southern Africa, making up about 80% of the province's total estuarine area. The lake sits at the heart of the iSimangaliso Wetland Park, which became South Africa's first UNESCO World Heritage Site in December 1999, and it has been recognized as a Ramsar Wetland of International Importance since 1986.

The system is famous for its extreme environmental shifts. Salinity can swing from nearly fresh to over 200 parts per thousand (ppt)—almost six times saltier than seawater—making Lake St Lucia a global benchmark for estuarine research. Over 60 years of peer-reviewed studies culminated in the 2013 Cambridge University Press book *Ecology and Conservation of Estuarine Ecosystems: Lake St Lucia as a Global Model*.

**Geography**

*Location and dimensions* Lake St Lucia lies within the iSimangaliso Wetland Park on KwaZulu-Natal's northeastern coast, about 235 kilometers north of Durban. It occupies a drowned river valley formed 8,000 to 10,000 years ago during the Holocene transgression, when rising post-glacial seas flooded incised coastal valleys. The lake stretches 60 to 80 kilometers in length and ranges from 1 to 23 kilometers wide. Despite its large surface area, it averages only 0.9 meters deep, with a maximum depth of about 3 meters. This extreme shallowness relative to its size drives the system's notable environmental variability.

*Lake basins* The lake has three distinct sub-basins, each with different hydrological traits: - **False Bay**: The northernmost basin, which historically became isolated from the sea earliest and recorded the most extreme hypersaline conditions during droughts, with salinity exceeding 150–200 ppt in 2003. - **North Lake**: The central basin, fed by the Mkuze River through a large delta-swamp system. During the 2002–2007 ecological crisis, it dried severely, with water covering only about 10% of its area by July 2006. - **South Lake**: The southern basin, which generally keeps more stable salinity and connects to The Narrows. The Narrows is a winding tidal channel, 15 to 22 kilometers long, linking the lake basins to the estuary mouth.

*Shores* Two protected areas border the lake: - **Western Shores**: The drier western margin, with palmveld and savanna vegetation. This 25,000-hectare area was extensively rehabilitated after commercial forestry was removed between 2005 and 2013, and includes Charter's Creek and Fani's Island. It receives about half the rainfall of the Eastern Shores due to a rain shadow from the coastal dunes. - **Eastern Shores**: Coastal dune forest and grassland between the lake and the Indian Ocean, including Mission Rocks and access to Cape Vidal. It features some of the tallest vegetated coastal dunes in the world.

**Hydrology** Five rivers feed the system from catchments outside the park: the Mkuze, Mzinene, Hluhluwe, Nyalazi, and Mpate. These flow seasonally in summer, contributing about 50% of water input under normal conditions, with direct rainfall supplying the rest. The Mfolozi River, historically the largest freshwater source providing up to 60% of inflow, was artificially separated from St Lucia in 1952—a management decision with major ecological consequences.

*Salinity dynamics* During droughts, Lake St Lucia shows what researchers call a "reverse salinity gradient," documented by Forbes & Cyrus (1993). Normally, salinity drops from the ocean-connected mouth toward northern freshwater inputs. But when the mouth closes during prolonged droughts, the pattern flips: highest salinities occur in the shallow northern lakes due to evaporation, while lowest salinities persist near The Narrows and estuary area. This creates extraordinary salinity swings, from oligohaline conditions below 5 ppt to extreme hypersaline states over 200 ppt—the highest ever recorded, in late 2003 in False Bay. The system alternates between four ecological states: fresh, estuarine, marine (around 35 ppt), and hypersaline, with the marine-estuarine state dominant when the mouth functions normally.

**History**

*Etymology* Portuguese explorer Manuel de Mesquita Perestrelo named the lake "Santa Lucia" on 13 December 1575, Saint Lucy's Day, while charting the Southern African coast. Earlier Portuguese survivors of the São Bento shipwreck (1554) had called the broader area "Rio dos Medos do Ouro" (River of the Gold Dunes).

*Pre-colonial occupation* The Tsonga people have lived in this region for over 1,000 years, with archaeological evidence showing continuous occupation since at least the 13th century. Reverend Henri-Alexandre Junod's ethnographic studies from the 1890s recorded the Tsonga Tembe people's presence, noting that the Tembe capital was located in St Lucia Bay. Traditional fishing practices, such as the 700-year-old fish kraal tradition still used at nearby Kosi Bay, reflect deep cultural ties to these waters.

*Conservation history* After severe wildlife losses from ivory hunting—Robert Briggs Struthers alone shot over 1,000 hippos in the area during the 1850s—parts of St Lucia were declared a Game Reserve in 1895, making it one of Africa's oldest protected areas and the world's oldest formally protected estuary. The St Lucia Park was proclaimed in 1939, expanding protection.