Gombe Stream National Park

The Lake

Lake Tanganyika is Africa's longest and deepest lake, about 675 kms long, 70 kms wide, and as much as 1,440 meters deep in places. Unlike many of the Rift Valley lakes, which lie in closed drainage basins, Lake Tanganyika has an outlet at Kalemie in Zaire through which water flows to the Atlantic. Thus it has never built up a high concentration of minerals. It contains about 0.4 gram of mineral salts per liter, mostly magnesium carbonate and sodium carbonate, with lesser amounts of potassium chloride and calcium carbonate. It is slightly alkaline (pH 8.5) and its temperature is typically 230 C (730 F). Although the surface of the lake is often whipped by storms, there is little circulation in its depths. All of the lake's organisms live in the top 200-meter layer, as below that depth there is no oxygen.

The biological diversity of the lake exceeds that of all others in the Rift system. This is partly because of its great age—20 million years—and partly because of its size and weather patterns. For example, fish that prefer sheltered habitats may find themselves isolated in small bays or rock outcrops, separated by long stretches of steeply sloping wave-churned shingle, which form natural barriers. Over time, fish populations thus separated have evolved into different species.

Most of the lake's 250 species of fish are endemic, i.e. they live nowhere else. There are over 200 species of cichlids alone—these are mostly small deep-bodied fish, often brightly colored, and almost all are unique to this lake. There are some large fish as well: Nile perch, tigerfish, yellowbellies and others. But the most economically important fish is the tiny DAGAA (Stolothrissa tanganyikae), a silvery sardine-like fish measuring 10 cms or less. It is related to the marine herring, and originally may have entered the lake via the Zaire river system from the Atlantic. Dagaa eat plankton and live in immense shoals near the surface in open water.

Special thanks to Thomson Safaris and Tanzania National Parks for contributing Tanzanian information.

Published: 28 Apr 2002 | Last Updated: 15 Sep 2010
Details mentioned in this article were accurate at the time of publication

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