74
The lake never freezes because of its proximity
to the ocean. There is one mixing during the winter.
It stratifi es during summer. The success of sewage diversion scheme showed that eutrophication
is reversible at least in Lake Washington.
6.2.3 Lake Tahoe
It is (located 120° W, 39° N; altitude 1,898 m;
catchment area 1,242 km
2
; lake area 499 km
2 ;
lake volume 156 km
3 ; maximum depth 501 m;
mean depth 313 m; and outfl ow Truckee River)
situated on the border between California and
Nevada. It is one of the deepest lakes in North
America. It has clear water but is extremely
unproductive. The lake has a tourist appeal. But
its glass-like clarity is matched by its ecological
fragility. About 50,000 people now live there
permanently and far more come seasonally. From
1949 to 1960, >11 million fry of kokanee salmon
( Oncorhynchus nerka ) were introduced into the
lake to improve sport fi shing. Regular stocking
continued until 1969. In 1963–1965, 333,000
opossum shrimp ( Mysis relicta ) were also added
to the lake to provide food for fi sh and improve
the catch. Not until 1970 was it noticed that
Daphnia , previously abundant amongst the lake
zooplankton, had almost disappeared. Both lake
trout ( Salvelinus namaycush ) and kokanee
switched from eating Daphnia to Mysis.
While this is speculative, there seems to be
continued increase in the phytoplankton of Lake
Tahoe. It does again highlight the dangers and
complexities of introducing species to lakes
where they do not occur naturally. Nevertheless,
people who should know better continue to suggest further introductions into even the most
precious and fragile ecosystems.
6.2.4 Lakes Mendota, Wisconsin
and Green in the USA
These lakes were studied by some workers
(Rickett 1922 , 1924 ; Lind and Cottam 1969 ).
There used to be an almost continuous girdle of
submerged AM extending from 5.0 to 5.5 m.
Emergent and fl oating AM were few. Some of
the abundant AM are Nymphaea odorata , Lemna
minor , Wolffi a columbiana , etc. Sometimes,
there had been dramatic changes in the distribution and abundance of some of the species.
Green Lake was said to be more transparent than
Lake Mendota.
6.2.5 Lakes in UK: Land
of Many Lakes
There are regions in many places of the world
where zoological or hydrological events have
left a legacy, not of enormous which dominate
the landscape, but of many small lakes applied
relatively close together. Such lake districts are
particularly evident in areas which are affected
by intense glacial activity; and this had occurred
in mountainous country. Such landscapes had,
perhaps, formed combination of lake-fi lled valleys with mountains. This augments the scenic
beauty of the place. Such attractive lake areas
include the following: the lakes in European
Alps, the English Lake District and the glacierformed valleys converted to lakes in the
Southern Alps in New Zealand.
6.2.5.1 The English Lake District
These were said to be brought to the light by the
famous English poet William Wordsworth
through his beautiful poems. Several lakes are
formed often due to certain common factors in
the same geographical regions. However, it does
not mean that they are identical simply because
they owe their origin to a common cause. Indeed,
individual lakes in such a group may differ signifi cantly in size, shape and ecology. A particularly glaring example is provided by the
Windermere Lakes of Cumbria in lake district of
Northern England. These lakes form a region
which is collectively called English Lake District
with their spectacular mountainous surrounding.
The core of the lake district is dome of old
hard rocks from which a number of river valleys
drain out in a radial pattern like the spokes of
bicycle wheel. This pattern was already existing
since the pre-Ice Age (approx. 10,000 years).
6 Lakes of the World
The lake never freezes because of its proximity
to the ocean. There is one mixing during the winter.
It stratifi es during summer. The success of sewage diversion scheme showed that eutrophication
is reversible at least in Lake Washington.
6.2.3 Lake Tahoe
It is (located 120° W, 39° N; altitude 1,898 m;
catchment area 1,242 km
2
; lake area 499 km
2 ;
lake volume 156 km
3 ; maximum depth 501 m;
mean depth 313 m; and outfl ow Truckee River)
situated on the border between California and
Nevada. It is one of the deepest lakes in North
America. It has clear water but is extremely
unproductive. The lake has a tourist appeal. But
its glass-like clarity is matched by its ecological
fragility. About 50,000 people now live there
permanently and far more come seasonally. From
1949 to 1960, >11 million fry of kokanee salmon
( Oncorhynchus nerka ) were introduced into the
lake to improve sport fi shing. Regular stocking
continued until 1969. In 1963–1965, 333,000
opossum shrimp ( Mysis relicta ) were also added
to the lake to provide food for fi sh and improve
the catch. Not until 1970 was it noticed that
Daphnia , previously abundant amongst the lake
zooplankton, had almost disappeared. Both lake
trout ( Salvelinus namaycush ) and kokanee
switched from eating Daphnia to Mysis.
While this is speculative, there seems to be
continued increase in the phytoplankton of Lake
Tahoe. It does again highlight the dangers and
complexities of introducing species to lakes
where they do not occur naturally. Nevertheless,
people who should know better continue to suggest further introductions into even the most
precious and fragile ecosystems.
6.2.4 Lakes Mendota, Wisconsin
and Green in the USA
These lakes were studied by some workers
(Rickett 1922 , 1924 ; Lind and Cottam 1969 ).
There used to be an almost continuous girdle of
submerged AM extending from 5.0 to 5.5 m.
Emergent and fl oating AM were few. Some of
the abundant AM are Nymphaea odorata , Lemna
minor , Wolffi a columbiana , etc. Sometimes,
there had been dramatic changes in the distribution and abundance of some of the species.
Green Lake was said to be more transparent than
Lake Mendota.
6.2.5 Lakes in UK: Land
of Many Lakes
There are regions in many places of the world
where zoological or hydrological events have
left a legacy, not of enormous which dominate
the landscape, but of many small lakes applied
relatively close together. Such lake districts are
particularly evident in areas which are affected
by intense glacial activity; and this had occurred
in mountainous country. Such landscapes had,
perhaps, formed combination of lake-fi lled valleys with mountains. This augments the scenic
beauty of the place. Such attractive lake areas
include the following: the lakes in European
Alps, the English Lake District and the glacierformed valleys converted to lakes in the
Southern Alps in New Zealand.
6.2.5.1 The English Lake District
These were said to be brought to the light by the
famous English poet William Wordsworth
through his beautiful poems. Several lakes are
formed often due to certain common factors in
the same geographical regions. However, it does
not mean that they are identical simply because
they owe their origin to a common cause. Indeed,
individual lakes in such a group may differ signifi cantly in size, shape and ecology. A particularly glaring example is provided by the
Windermere Lakes of Cumbria in lake district of
Northern England. These lakes form a region
which is collectively called English Lake District
with their spectacular mountainous surrounding.
The core of the lake district is dome of old
hard rocks from which a number of river valleys
drain out in a radial pattern like the spokes of
bicycle wheel. This pattern was already existing
since the pre-Ice Age (approx. 10,000 years).
6 Lakes of the World