Standing water – lakes and ponds

Wales has about 500 lakes and large ponds, more than 1000 small ponds. Natural lakes and ponds were mainly created by the action of glaciers during the Ice Age, and so are particularly concentrated in north Wales.

Many of the upland lakes are clear and are comparatively poor in nutrients. An increasing number of lakes and ponds are becoming enriched by minerals like nitrogen and phosphorus, which can cause conservation problems.

Rich in nutrients – eutrophic lakes

Naturally occurring eutrophic lakes are the ‘richest’ lake types. They have fairly high concentrations of nutrients like nitrogen and phosphorus which help plantlife to grow.

Natural eutrophic lakes are rare in Wales, because the right combination of landscape and geology doesn’t happen often. Most examples are in Anglesey, Clwyd and Powys – the largest and best known is probably Llangorse Lake, near Brecon.

Because of the effect of human activity we know that many of the lakes we now consider eutrophic – the most rich in nutrients – were once considered medium-rich.

What are eutrophic lakes?

Eutrophic lakes are usually shallow and have a high diversity of water life. Although few and far between, these lakes are relatively important in Wales because they support a mixture of northern and southern wildlife that are threatened in the UK as a whole. They often have extensive areas of swamp and fen close by and these are threatened habitats in their own right. Many are important wildfowl sites.

Conservation

Eutrophic lakes with submerged broad-leaved pondweeds are protected under the Habitats Directive. Submerged broad-leaved pondweeds are tall-growing species, with beautiful flat see-through leaves. These plants are becoming steadily rarer throughout Europe, because they need lowland lakes with clear water.