Lake Malawi
Lake Malawi, also known as Lake Nyasa in Tanzania and Lago Niassa in Mozambique, is an African Great Lake and the southernmost lake in the East African Rift system, located between Malawi, Mozambique and Tanzania.
It is the fourth largest freshwater lake in the world by volume, the ninth largest lake in the world by area and the third largest and second deepest lake in Africa. Lake Malawi is home to more species of fish than any other lake in the world, including at least 700 species of cichlids. The Mozambique portion of the lake was officially declared a reserve by the Government of Mozambique on June 10, 2011, while in Malawi a portion of the lake is included in Lake Malawi National Park.
Lake Malawi is a meromictic lake, meaning that its water layers do not mix. The permanent stratification of Lake Malawi's water and the oxic-anoxic boundary are maintained by moderately small chemical and thermal gradients.
Geography
Lake Malawi is between and long, and about wide at its widest point. The lake has a total surface area of about. The lake is at its deepest point, located in a major depression in the north-central part. Another smaller depression in the far north reaches a depth of. The southern half of the lake is shallower; less than in the south-central part and less than in the far south.The lake has shorelines on western Mozambique, eastern Malawi, and southern Tanzania. The largest river flowing into it is the Ruhuhu River, and there is an outlet at its southern end, the Shire River, a tributary that flows into the Zambezi River in Mozambique. Evaporation accounts for more than 80% of the water loss from the lake, considerably more than the outflowing Shire River. The outflows from Lake Malawi into the Shire River are vital for the economy as the water resources support hydropower, irrigation and downstream biodiversity.
Concerns have been raised over the future climate change impacts of Lake Malawi due to the recent decline in lake levels and the overall drying trend. The climate in the lake region is already experiencing changes, with the temperatures predicted to increase throughout the country.
The lake is about southeast of Lake Tanganyika, another of the great lakes of the East African Rift.
The Lake Malawi National Park is located at the southern end of the lake.
Geological history
Malawi is one of the major Rift Valley lakes and an ancient lake. The lake lies in a valley formed by the opening of the East African Rift, where the African tectonic plate is being split into two pieces. This is called a divergent plate tectonics boundary. Malawi has typically been estimated to be 1–2 million years old, but more recent evidence points to a considerably older lake with a basin that started to form about 8.6 mya and deep-water condition first appeared 4.5 mya.The water levels have varied dramatically over time, ranging from almost below current level to above. During periods the lake dried out almost completely, leaving only one or two relatively small, highly alkaline and saline lakes in what currently are Malawi's deepest parts. A water chemistry resembling the current conditions only appeared about 60,000 years ago. Major low-water periods are estimated to have occurred about 1.6 to 1.0–0.57 million years ago, 420,000 to 250,000–110,000 years ago, about 25,000 years ago and 18,000–10,700 years ago. During the peak of the low-water period between 1390 and 1860 AD, it may have been below current water levels.
Water characteristics
The lake's water is alkaline and warm with a typical surface temperature between, while deep sections typically are about. The thermocline is located at a depth of. The oxygen limit is at a depth of approximately, effectively restricting fish and other aerobic organisms to the upper part. The water is very clear for a lake and the visibility can be up to, but slightly less than half this figure is more common and it is below in muddy bays. However, during the rainy season months of January to March, the waters are more muddy due to muddy river inflows.European colonisation
The Portuguese trader Candido José da Costa Cardoso was the first European to visit the lake in 1846. David Livingstone reached the lake in 1859, and named it Lake Nyasa. He also referred to it by a pair of nicknames: Lake of Stars and Lake of Storms. The Lake of Stars nickname came after Livingstone observed lights from the lanterns of the fishermen in Malawi on their boats, that resemble, from a distance, stars in the sky. Later, after experiencing the unpredictable and extremely violent gales that sweep through the area, he also referred to it as the Lake of Storms.On 16 August 1914, Lake Malawi was the scene of a brief naval battle during World War I. The British gunboat, commanded by a Captain Rhoades, received orders from the British Empire's high command to "sink, burn, or destroy" the German Empire's only gunboat on the lake, the, commanded by Captain Berndt. Rhoades's crew found the Hermann von Wissmann in a bay near Sphinxhaven, in German East African territorial waters. Gwendolen disabled the German boat with a single cannon shot from a range of about. This brief conflict was hailed by The Times in England as the British Empire's first naval victory of World War I.
Borders
Tanzania–Malawi dispute
The partition of the lake's surface area between Malawi and Tanzania is under dispute. Tanzania claims that the international border runs through the middle of the lake. On the other hand, Malawi claims the whole of the surface of this lake that is not in Mozambique, including the waters that are next to the shoreline of Tanzania. Malawi currently administers these waters. Both sides cite the Heligoland Treaty of 1890 between the United Kingdom and Germany concerning the border. The wrangle in this dispute occurred when the British colonial government, just after they had captured Tanganyika from Germany, placed all of the waters of the lake under a single jurisdiction, that of the territory of Nyasaland, without a separate administration for the Tanganyikan portion of the surface. Later in colonial times, two jurisdictions were established.The dispute came to a head in 1967 when Tanzania officially protested to Malawi; however nothing was settled. Occasional flare-ups of conflict occurred during the 1990s and in the 21st century. In 2012, Malawi's oil exploration initiative brought the issue to the fore, with Tanzania demanding that exploration cease until the dispute was settled.
Malawi–Mozambique border
In 1954, an agreement was signed between the British and the Portuguese making the middle of the lake their boundary with the exception of Chizumulu Island and Likoma Island, which were kept by the British and are now part of Malawi.Transport
began service on the lake in 1901 as the SS Chauncy Maples: a floating clinic and church for the Universities' Mission to Central Africa. She later served as a ferry and is currently being renovated into a mobile clinic at Monkey Bay. The renovation was expected to be complete during the first half of 2014, but was halted in 2017. entered service in 1935. The ferry entered service in 1951. In recent years she has often been out of service, but when operational she runs between Monkey Bay at the southern end of the lake to Karonga on the northern end, and occasionally to the Iringa Region of Tanzania. The ferry entered service in 1980. By 1982 she was carrying 100,000 passengers each year., but as of 2014 she was out of service. She normally serves the southern part of the lake but if Ilala was out of service she operated the route to Karonga. The Tanzanian ferry was built in 1988. Her operator was the Tanzania Railway Corporation Marine Division until 1997, when it became the Marine Services Company Limited. Songea plies weekly between Liuli and Nkhata Bay via Itungi and Mbamba Bay. The worst Lake disaster was the sinking of the in 1946, which resulted in 145 deaths.Wildlife
Wildlife found in and around Lake Malawi or Nyasa includes Nile crocodiles, hippopotamus, monkeys, and a significant population of African fish eagles that feed off fish from the lake.Fish
Fishing
Lake Malawi has for millennia provided a major food source to the residents of its shores since its waters are rich in fish. Among the most popular are the four species of chambo, consisting of any one of four species in the subgenus Nyasalapia, as well as the closely related O. shiranus. Other species that support important fisheries include the Lake Malawi sardine and the large kampango catfish. Most fishing provides food for the increasing human population near the lake, but some are exported from Malawi. The wild population of fish is increasingly threatened by overfishing and water pollution. A drop in the lake's water level represents another threat, and is believed to be driven by water extraction by the increasing human population, climate change and deforestation. The chambo and kampango have been particularly overfished and they are now seriously threatened. The IUCN recognises 117 species of Malawi cichlids as threatened; some of these have tiny ranges and may be restricted to rocky coastlines only a few hundred metres long.Cichlids
Lake Malawi is noted for being the site of evolutionary radiations among several groups of animals, most notably cichlid fish. There are at least 700 cichlid species in Lake Malawi, with some estimating that the actual figure is as high as 1,000 species. The actual number is labelled with some uncertainty because of the many undescribed species and the extreme variation among some species, making the task of delimiting them very complex. Except for four species, all cichlids in the lake are endemic to the Malawi system, which also includes nearby smaller Lake Malombe and the upper Shire River. Many of these have become popular among aquarium owners due to their bright colors. Recreating a Lake Malawi biotope to host cichlids became quite popular in the aquarium hobby. Most Malawi cichlids are found in relatively shallow coastal waters, but Diplotaxodon has been recorded down to depths of and several are known from pelagic waters.The cichlids of the lake are divided into two groups and the vast majority of the species are haplochromines. The sister species to the Malawi haplochromines is Astatotilapia sp. Ruaha, and these two separated between 2.13 and 6.76 million years ago. The earliest divergence within the Malawi haplochromines occurred between 1.20 and 4.06 mya, but most radiations in this group are far younger; in extreme cases species may have diverged only a few hundred years ago. The Malawi haplochromines are mouthbrooders, but otherwise vary extensively in general behaviour and ecology. Within the Malawi haplochromines there are two main groups, the haps and the mbuna. The haps can be further subdivided into three subgroups: The relatively large, often more than long, and aggressive piscivores that roam various habitats in pursuit of prey, the open-water utaka that feed in schools on zooplankton and typically are of medium size, and finally a subgroup of "aberrant" species that essentially are defined by them not fitting clearly into the other subgroups. Adult male haps generally display bright colors, while juveniles of both sexes and adult females typically show a silvery or grey coloration with sometimes irregular black bars or other markings. The second main haplochromine group are the mbuna, a name used both locally and popularly, which means "rockfish" in Tonga. They are found at rocky outcrops, territorially aggressive and often specialised aufwuchs feeders. The mbuna species tend to be relatively small, mostly less than long, and often both sexes are brightly colored with males having egg-shaped yellow spots on their anal fin.
The second group, the tilapia, comprises only six species in two genera in Lake Malawi: The redbreast tilapia, a widespread African species, is the only substrate-spawning cichlid in the lake. This large cichlid mainly feeds on macrophytes. The remaining are five mouthbrooding species of Oreochromis; four chambo in the subgenus Nyasalapia that are endemic to the Lake Malawi system, as well as the closely related O. shiranus, which also is found in Lake Chilwa. The Malawi Oreochromis mainly feed on phytoplankton, reach lengths up to depending on the exact species, and are mostly black or silvery-gray with relatively indistinct dark bars. Male chambo have unique genital tassels when breeding, which aid in egg fertilisation in a manner comparable to the egg-spots on the anal fin of haplochromines.