Lake Malawi
Lake malawi is a very important lake to the natives living aroud the lake. More than 10 000 tons of fish is caught every year, mostly Utaka (haplocromian cichlids),cambo (Tilapian cichlids) and the lake sardin usipa.
The lake is the nineth largest in the world with a length of 600 km and a maximum width of 80 km. It is 700 m deep in the deepest part and it cowers an area of 31 000 km2.
The lake is surrounded by three countries. Most of the lake (the western and southern parts) belong to Malawi, the north eastern part belongs to Tanzania and a large part of the eastern shore belongs to Mozambique.
In spite of the depth of the lake (700 m), water layers beyond 200 meters arevoid of dissolved oxygene. This phenomenon is common in tropical lakes without extreme season changes (spring, fall) that cool the water layers onthe surface and make the water circulate.
The water temperature is fairly stabile between 23oC and 28oC.
The water chemistry is (as in all rift valley lakes) interesting. The pH variesbetween 7.8 and 8.5. The difference in pH is caused by the level of CO2 dissolved in the water. The pH is higher in turbulent water where it is better aerated. In calm bays, the level of dissolved CO2 is higher and therefore the pH is lower here.
The conductivity (a measurement of the amount of dissolved minerals in thewater) varies between 200-260 mS (microSiemens).
The sight in the water is good (often more than 20 m) except when the algaebloom. The waterlevel varies with the seasons, but in the latest 10 years the waterlevel has drastically decreased.
These drastic changes of waterlevel is actually one of the reasons why the large number of species have evolved (more than 600 cichlid species known today).
The waterlevel has varied a lot during the years. 25 000 years ago theshore was 400 meters below the present one. The age of the lake is not fullystated yet, but it is probably between 5 and 20 million years old.
The coastline consists of three different types. The rocky areas coverabout one third of the coast (this is the home of the mbunas).
Most of the remaining parts of the shore are covered with sand. The third biotope are where larger rivers flow in. These areas of mud and weed work as aborder between geografical variants and different cichlids species (rockliving cichlids have difficulties in crossing these areas).
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