Lake Malawi

• Category: Inland Aquatic Biomes.
• Geographic Location: Africa.
• Summary: Lake Malawi, the southernmost major lake in the Great Rift Valley of East Africa, is recognized as a global biodiversity hot spot.

Lake Malawi (known as Lake Nyasa in many countries) is located in East Africa at the juncture of the countries of Malawi, Mozambique, and Tanzania. It is in the Great Rift Valley, which began evolving at least 1 million years ago when the African tectonic plate split and created volcanic valleys that feature a string of great lakes: Malawi, Tanganyika, Victoria, and four others of lesser scale. The Rift Valley system includes some of the oldest, largest, and deepest lakes in the world; many of these freshwater ecosystems support vast biodiversity and specialized organisms.

The Rift Valley lakes are known for the evolution of hundreds of cichlid fish species. Few, if any, other bodies of water on the planet have as many species of freshwater fish as Lake Malawi. Because Lake Malawi and the other Rift Valley lakes represent ecosystems of such vast and specialized biodiversity, the World Wildlife Fund included the lakes in its Global 200 priority ecoregions for conservation.

Hydrology

Lake Malawi is the second-deepest lake in Africa, and is among the 10 largest lakes in the world. With a maximum depth of 2,316 feet (706 meters) and surface area of approximately 11,430 square miles (29,600 square kilometers), the total lake volume is estimated at 2,015 cubic miles (8,400 cubic kilometers). The water is generally warm, with temperatures near the surface ranging from 75 to 84 degrees F (24 to 29 degrees C). The deeper water runs several degrees cooler—averaging about 72 degrees F (22 degrees C) year-round. Due to the geological makeup of Lake Malawi, it is slightly alkaline (pH 7.7 to 8.6), with a carbonate hardness of 28.27 to 37.51 parts per million.

Located approximately 220 miles (350 kilometers) southeast of Lake Tanganyika, the largest portion of Lake Malawi is located in the nation of Malawi, with about one-quarter of the area belonging to Mozambique; these two countries, along with Tanzania, each claim some shoreline rights and occasionally air disputes over fishing rights in different areas of the lake.

Of hydrologic importance, the largest river that flows into Lake Malawi is the Tanzanian river Ruhuhu, flowing into the east side; the Shire River, a tributary of the Zambezi River, drains the lake from its southern shore. Only two islands—Likoma and Chizumulu—are inhabited. Characteristic of both islands is the abundance of baobab trees (Adansonia digitata), which are commonly referred to as “the upside-down tree” or the “tree of life.” Both islets support several thousand fishers and farmers who grow a variety of food crops including cassavas, bananas, and mangoes.

Biodiversity

Lake Malawi is a rocky lake with few aquatic plant species; however, its banks feature wetlands and forests. The latter are a regionally valued source of timber for building and fuel. Notable trees include Mulanje cedar (Widdringtonia cuppresoides), mlombwa (Pterocarpus angloensis), and mbawa (Khava anthotheca).

Lake Malawi is home to a vast array of wildlife, including the painted hunting dog, which until recently was thought to be extinct; more prevalent are crocodiles, hippopotamuses, monkeys, and a large population of African fish eagles. Lake Malawi is probably best known for its diversity of fish. The tropical waters here are home to more than 1,000 species of fish, including unique types of cichlid, which is a family of which tilapia and sunfish are characteristic members.

In addition to cichlids, Lake Malawi is home to a plethora of other fish, including large populations of species belonging to families including Clariidae, Claroteidae, Mochokidae, Poeciliidae, Mastacembelidae, Centropomidae, Cyprinidae, and Clupeidae. While many such fish provide a major food source for other fauna, these populations are threatened by overfishing and pollution.

Preservation and Threats

Lake Malawi National Park was established specifically to conserve the lake’s globally-recognized biodiversity among fish species and habitat niches. The park encompasses approximately 36.3 square miles (94 square kilometers) at the southern end of Lake Malawi, of which about 3 square miles (7 square kilometers) represents aquatic habitats, protecting some important vegetation types and breeding areas.

Also featured are rocky shorelines, sandy beaches, wooded hillsides, swamps, lagoons, granitic hills, and sandy bays. About half of all fish species within Lake Malawi are thought to occur in the park—including nearly all of the hundreds of mbuna cichlid species.

Unfortunately, because of the small area of the park in relation to the lake, many Lake Malawian animal and plant species are unprotected. The World Heritage Committee of the United Nations Educational, Scientific and Cultural Organization (UNESCO) has recommended that the scope of the park be extended. The integrity of the park relies on the conservation and management of the lake, which falls under the jurisdiction of three sovereign states—Malawi, Tanzania, and Mozambique—which in some ways complicates the matter.

Serious climate change impacts have already been felt in Lake Malawi. These include dry spells and droughts, many of which have seriously affected the spawning and feeding protocols of its denizens. Floods have also increased in frequency, duration, and severity. Dislocation of habitat due to these pressures is adding to the challenge of conserving the lake biome’s richness against other anthropogenic factors. Increased temperatures may also lead to more frequent algae blooms, which decreases oxygen levels in the lake and can result in the death of fish.

Bibliography

Arnegard, Matthew E., et al. “Population Structure and Colour Variation of the Cichlid Fish Labeotropheus fuelleborni Ahl Along a Recently Formed Archipelago of Rocky Habitat Patches in Southern Lake Malawi.” Proceedings of the Royal Society of London 266, no. 1 (1999).

Lloyd, Evan, et.al. "Diversity in Rest-Activity Patterns Among Lake Malawi Cichlid Fishes Suggests Novel Axis of Habitat Partitioning." Journal of Experimental Biology, vol. 224, no.7, 1 Apr. 2021, doi.org/10.1242/jeb.242186. Accessed 11 Nov. 2024.

Network of International Development Organisations (NIDOS). “Malawi Climate Change Fact Sheet.” NIDOS in Scotland, 2009. .

Olson, David M. and Eric Dinerstein. “The Global 200: Priority Ecoregions for Global Conservation.” Annals of the Missouri Botanical Gardens 89, no. 2 (2002).