<P> Others, however, are shallow, and hardly reach the steep sides of the valleys in the dry season . Such are Lake Rukwa, in a subsidiary depression north of Nyasa, and Eiassi and Manyara in the system of the Great Rift Valley . Lakes of the broad type are of moderate depth, the deepest sounding in Lake Victoria being under 90 m (300 ft). </P> <P> Besides the African Great Lakes, the principal lakes on the continent are: Lake Chad, in the northern inland watershed; Bangweulu and Mweru, traversed by the head - stream of the Congo; and Lake Mai - Ndombe and Ntomba (Mantumba), within the great bend of that river . All, except possibly Mweru, are more or less shallow, and Lake Chad appears to be drying up . </P> <P> Divergent opinions have been held as to the mode of origin of the African Great Lakes, especially Tanganyika, which some geologists have considered to represent an old arm of the sea, dating from a time when the whole central Congo basin was under water; others holding that the lake water has accumulated in a depression caused by subsidence . The former view is based on the existence in the lake of organisms of a decidedly marine type . They include jellyfish, molluscs, prawns, crabs, etc . </P> <Table> <Tr> <Th> Lake </Th> <Th> m </Th> <Th> ft </Th> </Tr> <Tr> <Td> Chad </Td> <Td> 259 </Td> <Td> 850 </Td> </Tr> <Tr> <Td> Mai - Ndombe </Td> <Td> 335 </Td> <Td> 1100 </Td> </Tr> <Tr> <Td> Turkana </Td> <Td> 381 </Td> <Td> 1250 </Td> </Tr> <Tr> <Td> Malawi </Td> <Td> 501 </Td> <Td> 1645 </Td> </Tr> <Tr> <Td> Albert </Td> <Td> 618 </Td> <Td> 2028 </Td> </Tr> <Tr> <Td> Tanganyika </Td> <Td> 800 </Td> <Td> 2624 </Td> </Tr> <Tr> <Td> Ngami </Td> <Td> 899 </Td> <Td> 2950 </Td> </Tr> <Tr> <Td> Mweru </Td> <Td> 914 </Td> <Td> 3000 </Td> </Tr> <Tr> <Td> Edward </Td> <Td> 916 </Td> <Td> 3004 </Td> </Tr> <Tr> <Td> Bangweulu </Td> <Td> 1128 </Td> <Td> 3700 </Td> </Tr> <Tr> <Td> Victoria </Td> <Td> 1134 </Td> <Td> 3720 </Td> </Tr> <Tr> <Td> Abaya </Td> <Td> 1280 </Td> <Td> 4200 </Td> </Tr> <Tr> <Td> Kivu </Td> <Td> 1472 </Td> <Td> 4829 </Td> </Tr> <Tr> <Td> Tana </Td> <Td> 1734 </Td> <Td> 5690 </Td> </Tr> <Tr> <Td> Naivasha </Td> <Td> 1870 </Td> <Td> 6135 </Td> </Tr> </Table>

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