Lake Malawi is an African Great Lake, located on the Tanzania-Mozambique-Malawi border and known as Nyasa in Tanzania and Lago Niassa in Mozambique. Lake Malawi is Africa’s third-largest and the world’s ninth-largest lake by surface area, covering 29,600 sq. km. It is the world’s sixth-deepest and Africa’s second-deepest lake by maximum depth. However, it is the world’s fifth-largest freshwater lake by total volume. The lake has the highest fish species of any lake in the world. It is an example of a meromictic lake whose water layers do not intermix.
Lake Malawi is 560-580 km long from north to south and has a maximum width of 75 km. The lake is located at an elevation of 468 m above sea level and has an average depth of 292 m. It is 706 m deep at the deepest point, a north-central point lying in a major depression. The extreme northern part also lies in a depression, with the depth reaching 528 m. The southern portion is the lake’s shallow end, which reaches a depth of between 200 and 400 m. Lake Malawi has a volume of 8,400 cubic kilometers.
This meromictic lake has three water layers of varying densities and temperatures. The surface layer has a temperature between 24°-29°C,while the deeper layers are colder, with a temperature of 22°C. The thermocline layer is at a depth of 40-100 meters, while oxygen is limited to a maximum depth of 250 meters. Thus, obligated aerobes are restricted to the upper part.
Although Lake Malawi receives inflow from several rivers and streams, the Ruhuhu River is the largest river emptying into the lake. The Ruhuhu River rises in the Kapengere Range in Tanzania’s Ruvuma Region and flows for about 160 km before draining into eastern Lake Malawi. The Lake’s main outlet is the Shire River, which drains the lake on the south and feeds the larger Zambezi River. However, up to 80% of the lake’s water is lost through evaporation.
Lake Malawi is one of the largest Rift Valley lakes and an ancient lake in the East African Rift, a rift zone with an active continental plate. The lake is about two million years old, though its basin may have started forming over 8.6 million years ago. Over the years, the water level has varied between 600 and 10 m. At some point, the lake almost completely dried out, leaving small saline lakes in some of its deepest parts. The period of low water level was between 1.6 and 1.0 million years ago and the lake may have completely dried out during this period.
Lake Malawi lies on the Tanzania-Malawi-Mozambique border and has a shoreline on eastern Malawi, western Mozambique, and southern Tanzania. Parts of the Tanzania-Malawi and Malawi-Mozambique border and the tripoint is located in the lake. While Tanzania claims its boundary with Malawi lies in the middle of the lake, Malawi insists the whole of the lake’s portion not in Mozambique is part of its territory. The conflict resulted from the 1890 Heligoland Treaty between the British and Germans, with the British placing the waters of the entire lake in Nyasaland. The Malawi-Mozambique border, defined in 1954 by the Portuguese and British, is a line passing through the middle of the lake. This boundary is undisputed.
Lake Malawi has the world’s highest number of fish species, and fishing is a major economic activity around the lake. However, the fish population is threatened by pollution and overfishing. Popular fish species include the chambos, Lake Malawi sardine, and kampango catfish. The majority of the fish in the lake are cichlids, numbering 700-1,000 species, all of which are endemic except four species; eastern river bream, redbreast tilapia, largemouth, and Oreochromis shiranus. The cichlids are divided into haplochromines and tilapia. The non-cichlids include airbreathing catfish, cyprinids, mochokid catfish, and the spotted killifish. Invertebrates in the lake include 28 freshwater snail species, 9 bivalves, blue crabs, glassworms, and atyid shrimp, among other species.