Background
The River Lyon is the main tributary of the upper
Tay and should be the engine house for salmon fisheries
in that area. However, the local feeling seems
to be that the Lyon is not the river it once was
and it is considerably less productive in terms
of salmon catches that some other Tay tributaries.
Like some other Tay tributaries the Lyon has
been significantly harnessed for hydro power
and there has for long been local concern that
this has reduced the productivity of the river.
A significant section of spawning area was lost
when a dam chopped off over 10km of its headwaters
and the flow is now controlled by a dam.
Within a few years of the construction of the
dams in the late 1950s local proprietors were
complaining about differences in the river, for
example the increased abundance of “slime” on
the stones.
Downstream effects of dams
For decades now it has become appreciated in
various parts of the world that the ecology
of rivers can be damaged downstream of dams.
While a considerable amount of research has
been conducted in North America especially
and even in England, almost nothing has been
done in Scotland. This research has found that
plant life, insect life and fish life are often
affected as a result of things like temperature
change, chemical changes and changes in the
flow regime.
Research on the Lyon
Concerned that similar impacts might be occurring
on the Lyon, several years ago the Board initiated
some studies on the river. Initially the Board
performed some of its own investigations which
revealed significant areas of concern, especially
regarding insects. Then to establish better information
on the effects on invertebrates an independent
study was conducted by researchers from the University
of Aberdeen. This was funded jointly by the Tay
Board, Tay Foundation and Scottish and Southern
Energy plc.
What’s
gone wrong with the River Lyon? Read about it here.
Aberdeen University study confirms an impact of
hydro dams. Access results here. |
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Over 10km of some of the best spawning grounds
on the Lyon were cut off as a result of the
construction of dams in the headwaters.
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In addition to the now flooded mainstem of
the Lyon the cut-off waters included the Meran
above and the Abhainn Ghlas below.
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Even downstream from the dams the insect
community has been altered. Such effects have
also been found in other parts of the world.
How many other Scottish rivers are affected
like this?
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Dense algal mats can cover the bed at certain
times of the year and the stones are dark because
of an iron / manganese precipitate. Such metals
are dissolved in the anaerobic water at the
bottom of the reservoir, from which the river
flow is drawn.
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The temperature of the water emerging from
the dam during the late spring and early summer,
a critical time for many biological events,
is much colder during fine weather than it
would naturally be.
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