Lake Malawi

Lake Malawi, also known asLake NyasainTanzaniaandLago NiassainMozambique, (Swahili:Ziwa Nyasa) is anAfrican Great Lakeand the southernmost lake in theEast African Riftsystem, located betweenMalawi, Mozambique and Tanzania.
It is thefourth largestfreshwater lake in the world by volume, theninth largestlake in the world by area and the third largest andsecond deepestlake in Africa. Lake Malawi is home to more species of fish than any other lake in the world,including at least 700 species ofcichlids.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 inLake Malawi National Park.
Lake Malawi is ameromictic lake, meaning that its water layers do not mix. The permanent stratification of Lake Malawi's water and the oxic-anoxicboundary are maintained by moderately small chemical andthermal gradients.
Lake Malawi is between 560 kilometres (350 mi)and 580 kilometres (360 mi) long,and about 75 kilometres (47 mi) wide at its widest point. The lake has a totalsurface areaof about 29,600 square kilometres (11,400 sq mi).The lake is 706 m (2,316 ft) at itsdeepest point, located in a majordepressionin the north-central part.Another smaller depression in the far north reaches a depth of 528 m (1,732 ft).The southern half of the lake is shallower; less than 400 m (1,300 ft) in the south-central part and less than 200 m (660 ft) in the far south.
The lake has shorelines on westernMozambique, easternMalawi, and southernTanzania. The largest river flowing into it is theRuhuhu River, and there is an outlet at its southern end, theShire River, a tributary that flows into theZambezi Riverin 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 350 kilometres (220 mi) southeast ofLake Tanganyika, another of the great lakes of the East African Rift.
TheLake Malawi National Parkis located at the southern end of the lake.
Malawi is one of the majorRift Valley lakesand anancient lake. The lake lies in a valley formed by the opening of theEast African Rift, where theAfrican tectonic plateis 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 (mya),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 600 m (2,000 ft) below current levelto 10–20 m (33–66 ft) above.During periods the lake dried out almost completely, leaving only one or two relatively small, highlyalkalineandsalinelakes 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 (where it might have dried out completely), 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 1860AD, it may have been 120–150 m (390–490 ft) below current water levels.
The lake's water is alkaline (pH7.7–8.6) and warm with a typical surface temperature between 24 and 29 °C (75–84 °F), while deep sections typically are about 22 °C (72 °F).Thethermoclineis located at a depth of 40–100 m (130–330 ft).Theoxygenlimit is at a depth of approximately 250 m (820 ft), effectively restricting fish and otheraerobic organismsto the upper part.The water is very clear for a lake and the visibility can be up to 20 m (66 ft), but slightly less than half this figure is more common and it is below 3 m (10 ft) in muddy bays.However, during the rainy season months of January to March, the waters are more muddy due to muddy river inflows.
ThePortuguesetrader Candido José da Costa Cardoso was the firstEuropeanto visit the lake in 1846.David Livingstonereached 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 duringWorld War I. The BritishgunboatSSGwendolen, 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, theHermann von Wissmann, commanded by Captain Berndt. Rhoades's crew found theHermann von Wissmannin a bay nearSphinxhaven, inGerman East Africanterritorial waters.Gwendolendisabled the German boat with a singlecannonshot from a range of about 1,800 metres (2,000 yd). This brief conflict was hailed byThe TimesinEnglandas the British Empire's first naval victory of World War I.
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.Both sides cite theHeligoland Treaty of 1890between Great Britain 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 ofNyasaland, without a separate administration for theTanganyikanportion 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.
In 1954, an agreement was signed between theBritishand thePortuguesemaking the middle of the lake their boundary with the exception ofChizumulu IslandandLikoma Island, which were kept by the British and are now part of Malawi.
MVChauncy Maplesbegan service on the lake in 1901 as the SSChauncy Maples: a floating clinic and church for theUniversities' Mission to Central Africa. She later served as a ferry and is currently being renovated into a mobile clinic atMonkey Bay. The renovation was expected to be complete during the first half of 2014, but was halted in 2017.MVMpasaentered service in 1935.The ferryMVIlalaentered 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 toKarongaon the northern end, and occasionally to theIringa Regionof Tanzania. The ferryMVMtendereentered 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 ifIlalawas out of service she operated the route to Karonga. The Tanzanian ferryMVSongeawas built in 1988.Her operator was theTanzania Railway CorporationMarine Division until 1997, when it became theMarine Services Company Limited.Songeaplies weekly between Liuli andNkhata Bayvia Itungi andMbamba Bay.The worst Lake disaster was the sinking of theMVVipyain 1946, which resulted in 145 deaths.
Wildlife found in and around Lake Malawi or Nyasa includesNile crocodiles,hippopotamus,monkeys,and a significant population ofAfrican fish eaglesthat feed off fish from the lake.
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 subgenusNyasalapia(Oreochromis karongae,O. lidole,O. sakaandO. squamipinnis), as well as the closely relatedO. shiranus.Other species that support important fisheries include theLake Malawi sardine(Engraulicypris sardella) and the largekampangocatfish (Bagrus meridionalis).Most fishing provides food for theincreasing human populationnear the lake, but some are exported from Malawi. The wild population of fish is increasingly threatened byoverfishingandwater 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 changeanddeforestation.The chambo and kampango have been particularly overfished (the kampango declined by about 90% from 2006 to 2016,O. karongaeandO. squamipinnisby about 94%, andO. lidolemight already be extinct) and they are now seriouslythreatened.TheIUCNrecognises 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.
Lake Malawi is noted for being the site ofevolutionary radiationsamong several groups of animals, most notablycichlidfish.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 manyundescribed speciesand the extreme variation among some species, making the task of delimiting them very complex.Except for four species (Astatotilapia calliptera,Coptodon rendalli,Oreochromis shiranusandSerranochromisrobustus), all cichlids in the lake areendemicto the Malawi system, which also includes nearby smallerLake Malombeand the upper Shire River.Many of these have become popular amongaquariumowners 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,butDiplotaxodonhas been recorded down to depths of 200–220 m (660–720 ft) and several (especiallyDiplotaxodon,RhamphochromisandCopadichromis quadrimaculatus) are known frompelagicwaters.
The cichlids of the lake are divided into two groups and the vast majority of the species arehaplochromines. Thesister speciesto the Malawi haplochromines isAstatotilapiasp. Ruaha (a currently undescribed species fromGreat Ruaha River), and these two separated between 2.13 and 6.76 million years ago (mya).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 aremouthbrooders, but otherwise vary extensively in general behaviour and ecology.Within the Malawi haplochromines there are two main groups, the haps and thembuna. The haps (they were formerly included inHaplochromis) can be further subdivided into three subgroups: The relatively large, often more than 20 cm (8 in) long, and aggressivepiscivoresthat roam various habitats in pursuit of prey, the open-water (although often not far from sand or rocks)utakathat feed inschoolsonzooplanktonand 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" inTonga.They are found at rocky outcrops,territoriallyaggressive (although commonly found in high densities) and often specialisedaufwuchsfeeders.The mbuna species tend to be relatively small, mostly less than 13 cm (5 in) long, and often both sexes are brightly colored with males having egg-shaped yellow spots on theiranal fin(a feature particularly prevalent in the mbuna, but not exclusive to this group).
The second group, thetilapia, comprises only six species in two genera in Lake Malawi: Theredbreast tilapia(Coptodon rendalli), a widespread African species, is the only substrate-spawning cichlid in the lake.This large cichlid mainly feeds onmacrophytes.The remaining are five mouthbrooding species ofOreochromis; four chambo in the subgenusNyasalapia(O. karongae,O. lidole,O. sakaandO. squamipinnis) that are endemic to the Lake Malawi system, as well as the closely relatedO. shiranus, which also is found inLake Chilwa.The MalawiOreochromismainly feed onphytoplankton, reach lengths up to 26–42 cm (10–17 in) 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.
The vast majority of the fish species in the lake are cichlids. Among the non-cichlid native fish are several species ofcyprinids(in generaBarbus,LabeoandOpsaridium, and the Lake Malawi sardineEngraulicypris sardella),airbreathing catfish(BathyclariasandClarias, and the kampangoBagrus meridionalis),mochokid catfish(ChiloglanisandMalawi squeakerSynodontis njassae),Mastacembelusspiny eel,mormyrids(Marcusenius,MormyropsandPetrocephalus), theAfrican tetraBrycinus imberi, thepoeciliidAplocheilichthys johnstoni, thespotted killifish(Nothobranchius orthonotus), and themottled eel(Anguilla nebulosa).
At a genus level, most of these are widespread in Africa, butBathyclariasis entirely restricted to the lake.
Lake Malawi is home to 28 species offreshwater snails(including 16 endemics) and 9bivalves(2 endemics,Aspatharia subreniformisand theunionidNyassunio nyassaensis).The endemic freshwater snails are all members of the generaBellamya,Bulinus,Gabbiella,LanistesandMelanoides.
Lake Malawi is home to a total of four snail species in the genusBulinus, which is a knownintermediate hostofbilharzia. A survey in Monkey Bay in 1964 found two endemic species of snails of the genus (B. nyassanusandB. succinoides) in the lake, and two non-endemic species (B. globosusandB. forskalli) in lagoons separated from it. The latter species are known intermediate hosts of bilharzia, and larvae of the parasite were detected in water containing these, but in experiments C. Wright of theBritish Museum of Natural Historywas unable to infect the two species endemic to the lake with the parasites. The field workers, who spent many hours on and in the lake, did not find eitherB. globosusorB. forskalliin the lake itself.More recently, the disease has become a problem in the lake itself as the endemicB. nyassanushas become an intermediate host. This change, first noticed in the mid-1980s, is possibly related to a decline in snail-eating cichlids (for example,Trematocranus placodon) due to overfishing and/or a newstrainof the bilharzia parasite.
Unlike Lake Tanganyika with its many endemicfreshwater crabsand shrimp, there are few such species in Lake Malawi. The Malawi blue crab,Potamonautes lirrangensis(syn.P. orbitospinus), is the only crab in the lake and it is not endemic.TheatyidshrimpCaridina malawensisis endemic to the lake, but it is poorly known and has historically been confused withC. nilotica, which is not found in the lake.Pelagiczooplanktonicspecies include twocladocerans(DiaphanosomaexcisumandBosmina longirostris), threecopepods(Tropodiaptomuscunningtoni,ThermocyclopsneglectusandMesocyclopsaequatorialis),and severalostracods(including both described andundescribed species).
Lake Malawi is famous for the huge swarms of tiny, harmless lake flies,Chaoborusedulis.These swarms, typically appearing far out over water, can be mistaken for plumes of smoke and were also noticed byDavid Livingstonewhen he visited the lake.The aquatic larvae feed on zooplankton, spending the day at the bottom and the night in the upper water levels.When theypupatethey float to the surface and transform into adult flies.The adults are very short-lived and the swarms, which can be several hundred metres tall and often have a spiraling shape, are part of their mating behaviour.They lay their eggs at the water's surface and the adults die.The larvae are an important food source for fish,and the adult flies are important both to birds and local people, who collect them to makekungucakes/burgers, a local delicacy with a very highproteincontent.
In January 2015, a sediment control tank collapsed at thePaladin Energy-owned uranium mine in Northern Malawi after a high intensity rain storm hit the area. It was revealed that approximately 50 litres of non radioactive material leaked into a local creek. Despite reports in local media ofradioactive contaminationthe government conducted independent scientific tests on the local river system and found that there was no effect on the environment.
The 25 km solo swim across Lake Malawi between Cape Ngomba and Senga Bay has been accomplished on 5 occasions by 16 swimmers
1992:Lewis Pugh9hrs 52 minutes (UK/South Africa)and Otto Thanning (South Africa) 10hrs 5 minutes
2010: Abigail Brown (UK) 9hrs 45 minutes
2013: Milko van Gool (Netherlands) 8hrs 46 minutesand Kaitlin Harthoorn (US) 9hrs 17 minutes
2016: (current record) Jean Craven (South Africa), Robert Dunford (Kenya), Michiel Le Roux (South Africa), Samantha Whelpton (South Africa), Greig Bannatyne (South Africa), Haydn Von Maltitz (South Africa), Douglas Livingstone-Blevins (South Africa) 7hrs 53 mins
2019: Chris Stapley (Eswatini) and Jay Azran (South Africa) 8hrs 40 minutes, Andrew Stevens (Australia) 10hrs 50 minutes, and Ruth Azran (South Africa) 11hrs 8 minutes.That same year, Martin Hobbs (South Africa), became the first person to swim the full length of Lake Malawi (54 days), as well as setting the world record for longest solo swim in a lake