Small tilapia fish caught in Lake Rukwa, Southwest Tanzania, are deep-fried before being sent to market in Mbeya, the commercial centre of the fertile Southern Highlands region. Lake Rukwa is a long, narrow lake lying in a basin of inland drainage southeast of Lake Tanganyika; it forms part of the Western Rift. The lake is very shallow (maximum depth not much more than twenty feet)) and mildly alkaline. Any change in its water level causes great fluctuations of its size.