What is ‘special’ about Llyn Llygeirian SSSI?

Llyn Llygeirian has two special features:

As well as the features listed above, Llyn Llygeirian has other habitats that contribute to the special interest. These include fringing reedswamp with bulrush, flowering rush and bottle sedge, willow scrub, trees and marshy grassland. This mixture of habitats is important for much of the wildlife including wildfowl, such as gadwall and whooper swan, other breeding birds, invertebrates and small mammals. Unless specified below, management of this site should aim to look after these habitats and species as well as the listed features of interest.

What do we want Llyn Llygeirian to look like?

Llyn Llygeirian should be a clear-water, moderately nutrient-rich freshwater lake with a diverse range of water plants. These should include uncommon

species such as frogbit, eight-stamened waterwort, six-stamened waterwort, needle spike-rush, spring quillwort and pillwort together with a wide range of more common water plants such as water milfoil, pondweeds and waterlilies.

The lake should be fringed with reedswamp and fen dominated by plants such as common reed, bottle sedge and bogbean. The site should support a diverse range of invertebrates including dragonflies. Areas of marshy grassland and woodland, which offer shelter to other plants, small mammals and nesting birds, should be found around the lake. A natural population of wild ducks should be present throughout the year with additional visiting birds such as gadwall and whooper swans in winter

In the long-term the lake may shrink as natural processes result in siltation, the expansion of swamp and development of wet woodland and other habitats. When this happens some aquatic species may be lost but new habitats will be provided for other species

What management is needed on Llyn Llygeirian SSSI and why?

Although Llyn Llygeirian is an excellent place for wildlife it will only remain so if the necessary management continues. CCW’s aim is to work with you to ensure that this management is carried out.

What does this mean in practice?

There are many factors that could damage the special features at Llyn Llygeirian if they are not properly managed. These are the ones we regard as most important:

Shooting: Llyn Llygeirian has been used for wildfowling in the past. Rearing large numbers of duck on site could cause localised damage by trampling and grazing of waterweeds and more widespread impacts by increasing nutrient levels in the lake. It is inappropriate on this site.

Fishing: Llyn Llygeirian is managed as a brown trout fishery, with approximately 500 trout being released annually. Artificial stocking of the lake with greater numbers or other fish species has the potential to destabilise the ecological balance of the lake and damage the special interest. Any changes to current fishery practices should consider the needs of the plants and animals found in the lake naturally.

Grazing: Grazing is important for the maintenance of marshy grassland with a wide range of different flowering plants. Cattle or ponies are generally the most appropriate stock for such areas. Stocking levels should be determined by the carrying capacity of the land and no supplementary feed should be provided (other than mineral licks). No drainage or reseeding should be carried out within the marshy grassland.

Water quality: Aquatic plants and animals depend on the quality of water in the lake. An increase in nutrient levels (e.g. phosphate and nitrate) may promote growth of species such as bulrush and water lily at the expense of less vigorous species of greater conservation interest. It may also cause algal “blooms” which can de-oxygenate the water, leading (in extreme cases) to fish-kills and, by blocking light can smother other plants and also lead to increased siltation, reducing the lifespan of the lake. Artificial inputs of nutrients (and other pollutants) should therefore be minimised. There should be no applications of herbicides, pesticides, lime or fertilisers of any kind, including artificial fertilisers, slurry, manure and abattoir or creamery waste, in or adjacent to the SSSI or its tributary streams. Farmyard drainage and sewage discharges should not be permitted to flow into the lake. There should also be no supplementary feeding of stock or dumping, spreading or storage of materials such as manure or silage bales on or adjacent to the SSSI.

Water quantity

The sluice on the outfall of Llyn Llygeirian should be maintained to retain water at current levels. No water should be abstracted or diverted from the lake or inflows in such quantities as to cause water levels to be lowered.

Motor boats

Motorboats have the potential to raise sediments and reduce the water quality of the lake thereby affecting plants and animals. There is also a risk from fuel leakage, especially during refuelling operations. The careful use of electric motors may be acceptable.

Invasive non-native plants: plants such as water fern, Japanese knotweed and Indian balsam are not known to occur at present, but have the potential to damage the value of the site. Care should be taken not to introduce these species deliberately or accidentally (e.g., on vehicle tyres or boots). Should they be discovered on site action may be required to control them.


The causeway across the lake (a public right of way) may require maintenance. Care is needed to avoid significant impacts on the lake.


Our knowledge of wildlife is far from complete. It is possible that new features of value may appear and new management issues may arise in the future, whilst other issues may disappear. This statement is written with the best information we have now, but may have to change in the future as our understanding improves. Any information you can provide on the wildlife of your site, its management and its conservation would be much appreciated.

If you would like to discuss any aspect of your SSSI, or have any concerns about your SSSI, please contact your local CCW office.

Your local office is;

Cyngor Cefn Gwlad Cymru/Countryside Council for Wales

North Wales Region

Llys y Bont,

Ffordd y Parc,

Parc Menai,


Gwynedd, LL57 4BN,

Telephone: 01248 672500

Fax: 01248 679259