Looking after the Bosherston Lakes

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The Bosherston Lakes were created by man, and are constantly being reclaimed by nature. The Cawdors built a series of dams and sluices between 1780 and 1860, but these structures and the lakes they formed depend on constant maintenance.

Two World Wars and the break-up of the estate in 1976 meant that the lakes went through a period of neglect, and have changed considerably in the last 30 years. Climate change is also having a profound effect, as will sea level rise in the future.

Water levels

The Bosherston Lakes get their water supply in two ways.

Streams flow directly into the Eastern Arm, and springs fed by an underground water supply feed the Central and Western Arms. Both the streams and the springs are dependent on rainfall, and water levels can vary by up to two metres between summer and winter.

Silt

The streams that flow into the lakes bring with them huge amounts of silt. This is basically topsoil that is washed off fields upstream by heavy rain. It brings with it fertiliser and manure, which raise the levels of nutrient in the lakes. This is bad for many of the special plants and animals which live in the lake.

What we can do

We can remove silt that has built up in the lakes over the last 200 years, and we have done this in some sections of the lake. This works well but is expensive.

Better still is to stop the silt reaching the lake in the first place. To do this we work with our partners and neighbours, looking at how the land is used in the surrounding area.

Sea level

The lakes are very close to sea level, and on rare occasions sea level can even be higher that that in the lakes. Sea levels are predicted to rise by a metre or more during this century.

It's no use just building a higher dam, because sea water is already able to enter the fresh water supply through holes in the limestone along the coast. The parts of the lakes nearest the sea are likely to become more saline in the next hundred years.

Climate change

The lakes are already two degrees warmer in summer than they were 20 years ago. This means changes to the plant and animal life in the lakes.

One sign of this is the increase in the amount of floating green algae during the summer months. We are working hard to decide how best to manage the lakes for the future.