The great lakes of Africa

Africa’s three largest lakes are located in East Africa. Deep depressions and rifts have formed here, due to the movement of the African and Arabian tectonic plates over the years. Large lakes have formed in the rifts. Lake Tanganyika and Lake Malawi are deep lakes with wide shores. Lake Victoria is shallow and wide and located outside the rifts themselves. The three lakes have enormous biodiversity, with many hundreds of species of endemic cichlids. In Lake Victoria, it is estimated that a new cichlid species evolves approximately every forty years. A very large proportion of cichlids are threatened with extinction as a result of eutrophication, deforestation, climate change and – above all – the introduction of invasive species in the lakes.

Lake Tanganyika was formed 20 million years ago and is about 1,500 metres deep. It is one of the oldest lakes in the world. Lake Malawi is 2.5 million years old and is extremely rich in biodiversity, with more than 700 species of cichlid fish living in the lake. Many of the fish species are adapted to the lake’s unique environment, and are found only there. Lake Victoria is a much younger lake. It was formed about 400,000 years ago, and is quite shallow. But Lake Victoria is the second largest freshwater lake in the world.

The Nile perch, fishing and biodiversity

The African lakes are important for the life around them. They provide surrounding rivers with fresh, nutrient-rich water. Many people make their living from fishing in the lakes. Birds and other animals also feed on the fish and plankton found there. When the predatory Nile perch was introduced into Lake Victoria in the 1950s, it quickly wiped out many native fish species, and much of the biodiversity was lost. Small fishing villages were replaced by large fishing industries, leading to fish depletion in the lake. But as the numbers of Nile perch declined due to overfishing, some native fish species began to recover. 

Eutrophication, deforestation and climate change

The lakes are also affected by changes in the environment around them. Lake Victoria has had major problems with environmental change. The invasive plant common water hyacinth has been spread to the lake by humans. Due to nitrogen and phosphorus emissions from agriculture and industry, the increased nutrients have caused the common water hyacinth to multiply rapidly. It now covers much of the shallow coastal waters of the lake, and the lake is suffering from eutrophication. 

Deforestation around the Great Lakes has also affected the nutritional balance of the lakes. When the forest is gone, there are no strong roots to help the soil stay in place when it rains. Large amounts of soil are then washed into the lakes. The substances in the soil affect life in the water, contributing to eutrophication. Climate change has also changed the way the wind behaves around the lakes. Winds are important for water currents that mix different nutrient layers in the lakes. Higher water temperatures due to global warming have reduced fish populations in the lakes.