What is ‘special’ about Llyn Llywenan SSSI?

Llyn Llywenan has 2 special features.

As well as the features listed above, Llyn Llywenan has other species and habitats that are key components of the special interest. These include an assemblage of wintering birds, a black-headed gull colony, breeding wildfowl including gadwall, and willow scrub. 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 Llywenan to look like?

What management is needed on Llyn Llywenan SSSI and why?

Although Llyn Llywenan is an excellent place for wildlife/geology 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 Llywenan if they are not properly managed. These are the ones we regard as most important:

Water quality: Any increase in nutrients (such as phosphates and nitrates) is likely to have an adverse effect on the lake and its wildlife. It may promote growth of a narrower range of plant species at the expense of the desired species. It may also promote algal “blooms” which smother natural plant populations, de-oxygenate the water and in extreme cases lead to loss of fish or other animal species. No agricultural fertiliser of any kind should be applied within 10m of the lakeshore. Silage and farmyard manure should not be stored within 20m of the lakeshore or of any inflowing stream. Care must also be taken in applying herbicides and pesticides in the vicinity of the lake.

Water quantity/level: This lake experiences significant draw-down each summer, due to its very small catchment. Whilst this is a natural process, any drainage or extraction of water which significantly increases this draw-down may have adverse effects. In particular, the remaining shallow water-body may become unacceptably warm and/or deoxygenated. This lake has been regulated by a dam in the past, but today this has fallen into disuse. Any proposal to restore this dam to a functional state should be the subject of consultation with CCW.

Angling and Fishery Management: Fish can affect the ecology of a lake by eating plants (altering the plant cover or composition) zooplankton or invertebrates or other fish or by stirring up nutrients in sediments. This lake has been managed at different times for eel, tench and trout fisheries. The long-term aim should be to enable a sustainable fishery to be established with natural recruitment by enhancement of the habitats available to fish, both in the lake and in streams and rivers with direct links to the lake. Stocking of trout, particularly brown trout, may be acceptable but no carp, bream or other voracious feeders or bottom feeders should be introduced. Any change in fishery management should be discussed with CCW.

Use of fishing boats is unlikely to have adverse effects providing that care is taken to avoid accidental pollution from engines. Engines should be well maintained to minimise risk of oil/fuel leaks caused by mechanical failure and to limit noise levels as far as possible. Speed should be limited to prevent damage to lake shore and vegetation by “wash”.

Predators and control: There has been a perceived problem with cormorants eating fish at this lake. They may be killed only under special license. Efforts must be made to show that no other way of dealing with the problem exists and that shooting cormorants is likely to be effective.

Shooting: This lake has been managed as a commercial shoot for many years. Low hides/butts have been constructed with narrow paths leading to them. These may be maintained but the operation should not intensify through increased number of guns or shooting days. Supplementary feeding of duck may introduce nutrients to the lake and should be avoided.

Natural succession/infilling: This lake is extremely shallow and likely to experience significant siltation in the coming decades/centuries. This is a natural process and should be allowed to take its course; the resultant wet woodland and swamp communities will be of interest in their own right, albeit different in nature to the existing lake and swamp. Dredging of the site would be highly disruptive and would merely postpone the inevitable. Opportunities for new, replacement water bodies should be sought in the vicinity.

Care should be taken to limit silt inputs to the lake; ploughing within the catchment should leave a buffer zone on the margins of any tributary or along the lake shore to prevent soil being washed into the lake. Stock should be allowed only limited access to the lake where essential for drinking water, since they can exacerbate siltation and nutrient enrichment. The remainder of the lake shore should be stockproofed.

Invasive non-native species: Plants such as water fern Azolla filiculoides, swamp stonecrop Crassula helmsii or Japanese knotweed Fallopia japonica can spread extremely rapidly and out-compete native species. These species are present on Anglesey and could be introduced by root fragment, fronds or other plant material. Any equipment, including machinery, fishing tackle and even boots and waders, brought on site should be thoroughly cleaned beforehand, regardless of whether they have been in contact with any invasive species. Measures should be taken to eradicate any accidental introductions as soon as possible.


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 Region

Llys y Bont,

Ffordd y Parc,

Parc Menai,


Gwynedd, LL57 4BN,

Telephone: 01248 672500

Fax: 01248 679259