Lake Malawi

Lake Malawi, also known as Lake Nyasa in Tanzania and Lago Niassa in Mozambique, is one of the African Great Lakes and the southernmost major lake of the East African Rift. Shared by Malawi, Mozambique and Tanzania, it is one of the world’s largest freshwater bodies: by volume it ranks among the deepest global lakes, while by surface area it is also one of the largest in Africa. The lake is renowned for its extraordinary biodiversity, especially its cichlid fish populations, and for its ancient geological history linked to the tectonic evolution of the East African Rift.

Biodiversity and Ecological Significance

Lake Malawi contains the greatest diversity of freshwater fish species of any lake on Earth. More than 700 species of cichlids have been identified, most of them endemic. This remarkable variety has made the lake a model system for evolutionary biology, particularly in studies of adaptive radiation. The Mozambican section of the lake was declared a reserve in 2011, and a large portion of the southern lakeshore in Malawi is protected within Lake Malawi National Park.
Lake Malawi is classed as a meromictic lake, meaning that its deep and shallow waters do not mix. Chemical and thermal gradients maintain stable stratification, giving the lake a persistent boundary between oxygenated upper waters and deeper anoxic layers. This structure has important implications for the distribution of aquatic life and for the lake’s long-term preservation of sediments and climatic records.

Geography and Hydrology

The lake extends over a substantial north–south distance. It lies within a rift depression where the African Plate is gradually dividing. The northern basin is extremely deep, while the southern half is shallower but still substantial. Its largest tributary is the Ruhuhu River, and its sole outlet is the Shire River at the southern end, which eventually joins the Zambezi River in Mozambique.
More than eighty per cent of the lake’s water loss occurs through evaporation, with outflow via the Shire River accounting for a comparatively small proportion. The Shire River is vital for regional hydropower generation, irrigation and the broader ecology of the Zambezi basin. In recent years, concerns have been raised about climate change impacts, declining lake levels and projections of increasing regional temperatures.
Lake Malawi is located approximately south-east of Lake Tanganyika, another major rift lake. Its southern end contains the Lake Malawi National Park, a UNESCO-listed site.

Geological History and Lake Evolution

Lake Malawi is an ancient lake formed within the East African Rift, a divergent tectonic boundary. Earlier estimates placed its age at around 1–2 million years, but more recent research indicates that the basin began forming about 8–6 million years ago, with deepwater environments established around 4–5 million years ago.
Throughout its history the lake’s water levels have experienced dramatic fluctuations. At times it has nearly dried out, leaving isolated saline lakes confined to the deepest depressions. During periods around 100 000 to 16 000 years ago, and again at intervals in the Late Pleistocene and early Holocene, the lake’s levels fell as much as several hundred metres below present levels. Conversely, high-water phases have raised levels significantly above today’s shoreline. The modern water chemistry, including its alkaline conditions, has existed consistently only in the last 60 000 years.
These drastic fluctuations have influenced species diversification, particularly among the lake’s cichlids, whose genetic divergence corresponds with repeated cycles of low-water periods.

Water Characteristics

Lake Malawi’s water is warm and alkaline, with surface temperatures typically between approximately 24°C and 29°C. Deep-water temperatures are more stable, remaining near 23°C. The thermocline generally occurs at moderate depth, and oxygen levels drop sharply below this point, restricting most fish species to the oxygenated upper layers.
Water clarity is high: visibility in the open lake can reach up to several tens of metres, though this varies by season. During the rainy months, increased river inflows reduce clarity, especially near river mouths.

European Exploration and Colonial Era

The first recorded European visitor to the lake was the Portuguese trader Cândido José da Costa Cardoso in 1846. The Scottish missionary-explorer David Livingstone reached the lake in 1859 and named it Lake Nyasa. He famously referred to it as the “Lake of Stars”, inspired by the glimmering lanterns of fishing boats at night, and as the “Lake of Storms” due to the violent winds common on its surface.
In August 1914 Lake Malawi was the site of an early naval engagement of the First World War. The British gunboat Gwendolen successfully disabled the German vessel Hermann von Wissmann near Liuli, an event reputed to be the British Empire’s first naval victory of the war.

International Borders and Disputes

The division of the lake’s surface between Malawi and Tanzania has long been contested. Tanzania maintains that the border should lie along the lake’s median line, whereas Malawi asserts that all waters not belonging to Mozambique fall under its jurisdiction. Both sides refer to historical agreements stemming from the Heligoland Treaty between Britain and Germany. Although disputes have arisen periodically—particularly in the 1960s, 1990s and again in the 2010s—no final settlement has been reached. Oil exploration activities have at times heightened diplomatic tensions.
The Malawi–Mozambique border is more clearly defined. A 1954 agreement between British and Portuguese authorities established a median-line boundary within the southern portion of the lake.

Regional Importance

Lake Malawi is central to the economies and societies of the surrounding countries. It supports fisheries, transport, hydropower and tourism. Its unique biodiversity attracts scientific interest from around the world, and its sediment records preserve valuable information about past climates. As part of the East African Rift system, the lake also serves as a natural laboratory for studying tectonic processes, evolutionary mechanisms and large-scale environmental change.