The two Cregennan Lakes, between Cadair
Idris and the Mawddach, are the best lakes in Wales with plants growing from a depth of over 8 metres
beneath the surface. This is double the depth of the average lake due to
the clarity of the water, the oxygenation and the lack of nutrients clogging up the natural
order of the system.
The land was given to the National
Trust by a man who lost both his sons in
the first world war. It’s a beautiful scene, but the real magic is beneath the surface with
a progression of different plants, such as water lobelia as you move from the shallows,
through quillworts, pondweeds, bladderworts and eventually to different types
of stonewort. Have a look at the film below to see some dive footage of what it
looks like.
A key thing to look at in determining
the quality of a lake is the level of
nutrients and the level of
dissolved oxygen. Excess nutrients come from sewage or agricultural run-off
and cause algal blooms which
reduce the oxygen levels. In a typical lake in the summer, the waters are
divided into cold water at the bottom with very little oxygen and warm water at
the top with lots of oxygen. But because of the wind and corresponding wave
action at Cregennan, it is constantly mixing up the cold and the warm water. Coupled
with the lack of nutrients, this
means the entire lake is well oxygenated throughout the year.
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