65
never completely mixed. The Lake Tanganyika
is younger (1.5–6 million years) than Lake
Baikal (50–75 million years). The lake is more
than 600 km long and has two major basins and
a smaller middle one. The Ruzizi River enters
at the north end of the lake, carrying rather
saline water from Lake Kivu. The other infl ows,
except the Malagarasi River, are rather short
and precipitous as they drain the adjacent
mountain ranges. The lake water generally
shows high conductivity (600 μS cm
1 ). The
present outfl ow which drains to the Zaire River
has not always been open ever since the fi rst
European explorers had arrived.
Lake Tanganyika contains many endemic
species. There are 60 species of molluscs in
contrast to 27 in Lake Malawi. Out of these, 30 of
the gastropod species of Lake Tanganyika are
endemic. Other endemics include two species of
aquatic snakes (cobra and krait). The aquatic
insects include the caddis fl y. It is interesting to
note here that similar species of caddis fl y had
also been reported from Lake Baikal and Lake
Titicaca in Andes. In Tanganyika, many molluscs
have thick shells and long spines, and the shape
of the shell looks like those of molluscs found
in the seashore. These characteristics are now
thought to be adaptations to similar environmental
conditions rather than evidence of a past connection between Lake Tanganyika and the sea.
Earlier connections have some indications that
Lake Tanganyika was remnant of the sea or it
could once have connection with the sea. When a
jellyfi sh was found in the open water, the case
seems to be proved, although there are many
objections to this view. However, some authors
had supported the idea of a marine origin for the
fauna of Lake Tanganyika. Further, the openwater fi sh fauna of Tanganyika was said to be
dominated by small clupeids, which are now
called Tanganyika sardines.
The algae in the open water of Lake Tanganyika
provide an excellent illustration of the difference
between standing crop and production. Standing
crop is the weight per unit area measured in dry
weight, or amount of carbon, present at one
particular time. Primary production is the amount
of new living material, measured as carbon fi xed
by photosynthesis per unit of time. In Lake
Tanganyika, the standing crop was low while primary production was high. Zooplankton in the
open water are also generally scanty. Diatoms are
usually abundant.
Yield of fi sh is very high as compared to primary production. The food chain could be very
effi cient. Non-mixing of the lake, in addition to
high transparency, could be the reasons for less
productivity.
6.1.4 Lakes in Uganda
6.1.4.1 Lake George (Wetland)
It is a shallow FW lake (0°,30°, 01′ E, altitude
913 m, area 250 km
2 , volume 600 million m
3 ,
max. depth 3.0 m approx., mean depth 2.4 m)
spanning the equator of Uganda in Africa. The
lake has a catchment area of 9,955 km
2 .
Mpanga River is the principal infl ow, while
Kazinga Channel is the main outfl ow. There
are two rainy and two dry seasons each year.
The location of Lake George at the foot of the
Ruwenzori Mountains also ensures that it
receives plenty of river infl ow all year-round.
Water from the eastern side of these mountains
pours down their steep slopes in innumerable
fast-fl owing streams that fl ow only a very short
distance over levelled ground to enter the
extensive papyrus swamps at the north end of
the lake. Water from the eastern escarpment of
the rift also drains to the lake. Water leaves the
lake via the broad shallow Kazinga Channel
which is 35 km long. It enters the much larger
and deeper Lake Edward. This drains north to
Lake Mobutu Sese Seko (formerly Lake Albert)
and the River Nile.
Lake George is remarkably stable in its physical
conditions and could reasonably be considered to
lack seasonal variation. Another major seasonal
factor of the lakes is wind. But Lake George is
partially shielded by the bulk of the mountains to
the northwest and by the escarpment close to the
lake. Sometimes, the wind is very strong enough
to stir the bottom mud under the water.
Occasionally, there are periods of calm when
stratifi cation may last for several days. Thus,
6.1 Lakes of Tropical Latitudes
never completely mixed. The Lake Tanganyika
is younger (1.5–6 million years) than Lake
Baikal (50–75 million years). The lake is more
than 600 km long and has two major basins and
a smaller middle one. The Ruzizi River enters
at the north end of the lake, carrying rather
saline water from Lake Kivu. The other infl ows,
except the Malagarasi River, are rather short
and precipitous as they drain the adjacent
mountain ranges. The lake water generally
shows high conductivity (600 μS cm
1 ). The
present outfl ow which drains to the Zaire River
has not always been open ever since the fi rst
European explorers had arrived.
Lake Tanganyika contains many endemic
species. There are 60 species of molluscs in
contrast to 27 in Lake Malawi. Out of these, 30 of
the gastropod species of Lake Tanganyika are
endemic. Other endemics include two species of
aquatic snakes (cobra and krait). The aquatic
insects include the caddis fl y. It is interesting to
note here that similar species of caddis fl y had
also been reported from Lake Baikal and Lake
Titicaca in Andes. In Tanganyika, many molluscs
have thick shells and long spines, and the shape
of the shell looks like those of molluscs found
in the seashore. These characteristics are now
thought to be adaptations to similar environmental
conditions rather than evidence of a past connection between Lake Tanganyika and the sea.
Earlier connections have some indications that
Lake Tanganyika was remnant of the sea or it
could once have connection with the sea. When a
jellyfi sh was found in the open water, the case
seems to be proved, although there are many
objections to this view. However, some authors
had supported the idea of a marine origin for the
fauna of Lake Tanganyika. Further, the openwater fi sh fauna of Tanganyika was said to be
dominated by small clupeids, which are now
called Tanganyika sardines.
The algae in the open water of Lake Tanganyika
provide an excellent illustration of the difference
between standing crop and production. Standing
crop is the weight per unit area measured in dry
weight, or amount of carbon, present at one
particular time. Primary production is the amount
of new living material, measured as carbon fi xed
by photosynthesis per unit of time. In Lake
Tanganyika, the standing crop was low while primary production was high. Zooplankton in the
open water are also generally scanty. Diatoms are
usually abundant.
Yield of fi sh is very high as compared to primary production. The food chain could be very
effi cient. Non-mixing of the lake, in addition to
high transparency, could be the reasons for less
productivity.
6.1.4 Lakes in Uganda
6.1.4.1 Lake George (Wetland)
It is a shallow FW lake (0°,30°, 01′ E, altitude
913 m, area 250 km
2 , volume 600 million m
3 ,
max. depth 3.0 m approx., mean depth 2.4 m)
spanning the equator of Uganda in Africa. The
lake has a catchment area of 9,955 km
2 .
Mpanga River is the principal infl ow, while
Kazinga Channel is the main outfl ow. There
are two rainy and two dry seasons each year.
The location of Lake George at the foot of the
Ruwenzori Mountains also ensures that it
receives plenty of river infl ow all year-round.
Water from the eastern side of these mountains
pours down their steep slopes in innumerable
fast-fl owing streams that fl ow only a very short
distance over levelled ground to enter the
extensive papyrus swamps at the north end of
the lake. Water from the eastern escarpment of
the rift also drains to the lake. Water leaves the
lake via the broad shallow Kazinga Channel
which is 35 km long. It enters the much larger
and deeper Lake Edward. This drains north to
Lake Mobutu Sese Seko (formerly Lake Albert)
and the River Nile.
Lake George is remarkably stable in its physical
conditions and could reasonably be considered to
lack seasonal variation. Another major seasonal
factor of the lakes is wind. But Lake George is
partially shielded by the bulk of the mountains to
the northwest and by the escarpment close to the
lake. Sometimes, the wind is very strong enough
to stir the bottom mud under the water.
Occasionally, there are periods of calm when
stratifi cation may last for several days. Thus,
6.1 Lakes of Tropical Latitudes