90
been fl owing down the escarpment have been
carrying increasing amount of silt which is
deposited as delta fans in the lake. At times,
this could alter the pattern of interaction
between the lake, its shoreline vegetation and
the animals which live there. The lake water is
too concentrated to sustain fi sh. However, it
does contain fi sh, except in the springs, around
its edge. The lake water also does not attract
large number of piscivorous birds.
6.6.12 Lake Rukwa
It is the most southerly situated lentic body in the
string of shallow saline lakes in East Africa. This
lake lies in an entirely separate rift of its own.
The lake occupies two basins, namely,
(a) The northern basin is so shallow that it
sometimes dries out completely.
(b) The southern basin is no where >6.5 m
deep. The water is not very highly saline. Hence,
it can usually support some normal species of
plants and animals. Aquatic fauna is more
diverse than in Lake Nakuru. Phytoplankton is
dominated by diatoms and not by BGA. Lake
Rukwa has some infl uence on the grazing game
animals. Migration of the animals into and out
of the Rukwa Valley coincides with fl uctuations
in the level of the lake. The patterns of expansion and contraction in the range of distribution
of large wild herbivores are easily accommodated by the natural ecosystem. However, they
may well be disrupted, if human settlement
occurs in areas which the animals only need at
irregular intervals when the lake levels are high.
This lake also sustains the largest breeding colony of great white pelicans ( Pelecanus onocrotalus ) . However, this pelican colony is also
vulnerable to fl uctuations in lake level. The
pelicans seem to be remarkably faithful to
their traditional nesting ground in spite of the
vicissitudes.
6.6.13 Lake Tahoe
Vide Sect. 6.2.3 .
6.7
Man-Made Lakes
Incidental consequence of quarrying and mining
subsidence could lead to the formation of artifi -
cial lakes. However, the largest lakes are formed
by damming a river valley forming a reservoir
of water behind the dam. Some parts of the
world, like South Africa, South America and the
Great Plains of North America, do not have
many natural lakes. In these areas, the number
and size of such reservoirs equal or exceed that
of natural waterbodies. However, most of these
reservoirs are small. They have been constructed
to fulfi l local purposes, like serving as water
stock for community water supply. But the
larger ones are built generally to supply water
and power to industries. It may be noted here
that, of late, it has been a matter of debate about
the extent to which the big dams could meet the
inadequacies for which they were built except
that they have been of major social, economic
and ecological consequence and have been a
bone of contention amongst many communities
and nations. Rather, these mega-dams, in addition to be an economic extravaganza, have been
responsible for altering pristine and virgin riverine ecosystem and transforming the coveted
lotic fauna into lacustrine, a change which is
irreversible and a damage which is irreparable.
Nevertheless, the number and scale of reservoir
projects have signifi cantly increased during the
last few decades. As such, the man- made lakes
are now signifi cant features of the landscape,
and their functioning is also a matter of national
and international importance. Big dams and
associated reservoirs are generally built to supply electricity, but at the cost of nature, how far
they could fulfi l this objective is a question in
many countries today. Often, the associated reservoirs are used to store water to be released
during the ‘lean’ season of reduced river fl ow, or
sometimes, the reservoirs are used to regulate
the fl ow of a river in order to control fl oods. To
the contrary, sometimes, due to the release of
huge volume of water during the rainy season,
the stored water of reservoirs, rather than controlling or managing fl oods, has been causing
6 Lakes of the World
been fl owing down the escarpment have been
carrying increasing amount of silt which is
deposited as delta fans in the lake. At times,
this could alter the pattern of interaction
between the lake, its shoreline vegetation and
the animals which live there. The lake water is
too concentrated to sustain fi sh. However, it
does contain fi sh, except in the springs, around
its edge. The lake water also does not attract
large number of piscivorous birds.
6.6.12 Lake Rukwa
It is the most southerly situated lentic body in the
string of shallow saline lakes in East Africa. This
lake lies in an entirely separate rift of its own.
The lake occupies two basins, namely,
(a) The northern basin is so shallow that it
sometimes dries out completely.
(b) The southern basin is no where >6.5 m
deep. The water is not very highly saline. Hence,
it can usually support some normal species of
plants and animals. Aquatic fauna is more
diverse than in Lake Nakuru. Phytoplankton is
dominated by diatoms and not by BGA. Lake
Rukwa has some infl uence on the grazing game
animals. Migration of the animals into and out
of the Rukwa Valley coincides with fl uctuations
in the level of the lake. The patterns of expansion and contraction in the range of distribution
of large wild herbivores are easily accommodated by the natural ecosystem. However, they
may well be disrupted, if human settlement
occurs in areas which the animals only need at
irregular intervals when the lake levels are high.
This lake also sustains the largest breeding colony of great white pelicans ( Pelecanus onocrotalus ) . However, this pelican colony is also
vulnerable to fl uctuations in lake level. The
pelicans seem to be remarkably faithful to
their traditional nesting ground in spite of the
vicissitudes.
6.6.13 Lake Tahoe
Vide Sect. 6.2.3 .
6.7
Man-Made Lakes
Incidental consequence of quarrying and mining
subsidence could lead to the formation of artifi -
cial lakes. However, the largest lakes are formed
by damming a river valley forming a reservoir
of water behind the dam. Some parts of the
world, like South Africa, South America and the
Great Plains of North America, do not have
many natural lakes. In these areas, the number
and size of such reservoirs equal or exceed that
of natural waterbodies. However, most of these
reservoirs are small. They have been constructed
to fulfi l local purposes, like serving as water
stock for community water supply. But the
larger ones are built generally to supply water
and power to industries. It may be noted here
that, of late, it has been a matter of debate about
the extent to which the big dams could meet the
inadequacies for which they were built except
that they have been of major social, economic
and ecological consequence and have been a
bone of contention amongst many communities
and nations. Rather, these mega-dams, in addition to be an economic extravaganza, have been
responsible for altering pristine and virgin riverine ecosystem and transforming the coveted
lotic fauna into lacustrine, a change which is
irreversible and a damage which is irreparable.
Nevertheless, the number and scale of reservoir
projects have signifi cantly increased during the
last few decades. As such, the man- made lakes
are now signifi cant features of the landscape,
and their functioning is also a matter of national
and international importance. Big dams and
associated reservoirs are generally built to supply electricity, but at the cost of nature, how far
they could fulfi l this objective is a question in
many countries today. Often, the associated reservoirs are used to store water to be released
during the ‘lean’ season of reduced river fl ow, or
sometimes, the reservoirs are used to regulate
the fl ow of a river in order to control fl oods. To
the contrary, sometimes, due to the release of
huge volume of water during the rainy season,
the stored water of reservoirs, rather than controlling or managing fl oods, has been causing
6 Lakes of the World