What is ‘special’ about Llyn Alaw SSSI?

Llyn Alaw has 4 special features:

As well as the features listed above, Llyn Alaw has other habitats that contribute to the special interest. These include small areas of woodland and scrub along parts of the lake shores, marshy grassland and scrub at the northern end, mud exposed around the margins of the lake at lower water levels and small islands in the reservoir. This mixture of habitats is important for much of the wildlife including wintering mallard, wigeon, goldeneye, pochard, tufted duck and sometimes pink-footed geese. Common terns and black-headed gulls nest on islands in the reservoir while tufted duck, mallard, great crested grebe and coot also breed here. The exposed muddy shore supports several unusual mosses including Weissia rostellata, Ephemerum sessile and Fissidens monguillonii. The wetland supports varied vegetation including sedges, purple moor grass, reed canary-grass, bulrush (reedmace) and other plants offering shelter and potential nest sites for birds including reed buntings. In autumn large flocks of waders, in particular curlew, lapwing and golden plover, feed on exposed muddy areas.

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 Alaw to look like?

What management is needed on Llyn Alaw SSSI and why?

Although Llyn Alaw 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 Alaw if they are not properly managed. These are the ones we regard as most important:

Water quality: As a moderately nutrient-rich body of water 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 also promotes algal “blooms” which smother natural plant populations, de-oxygenate the water and in extreme cases lead to loss of fish or other animal species. Developments in the catchment should be assessed for their potential to contribute to nutrient levels and options for reduced nutrient loads should be sought where possible. No fertiliser of any kind should be applied within 10metres of the lakeshore or any inflow stream. Silage and farmyard manure should not be stored within 20m of the lakeshore or of any inflow stream. Care must also be taken in applying herbicides or pesticides in the vicinity of the lake.

Water quantity/level: As the lake is shallow and is used as a reservoir it is subjected to significant fluctuations in water level, which exposes large areas of mud rich in invertebrates, an ideal feeding habitat for wading birds. Although this fluctuation should continue, any drainage or extraction beyond current practice may have adverse effects. In particular, the remaining shallow water-body may become unacceptably warm and/or deoxygenated.

Angling and Fishery Management: Fish can affect the ecology of a lake by eating plants (altering the plant cover or composition) zooplankton, invertebrates or other fish or by stirring up nutrients in sediments. This lake is currently managed as a rainbow and brown trout fishery. Stocking of trout, particularly brown trout, may be acceptable and natural spawning should be encouraged in the feeder streams. No carp, bream or other voracious feeders or bottom feeders should be introduced. Bank angling and the use of boats or float tubes should be limited to agreed areas outside the bird sanctuary. Any change in fishery management should be discussed with CCW.

Use of fishing boats in agreed areas, is unlikely to have adverse effects providing that care is taken to avoid disturbance to breeding birds and 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, islands and vegetation by “wash”.

Natural succession/infilling: Natural processes may result in increased siltation. When this happens some aquatic species may be lost but new habitats will be provided for other species.

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 lakeshore to prevent soil being washed into the lake. The lakeshore should continue to be stock proofed.

Scrub and woodland control: Small areas of scrub (including willow and alder) provide nesting places for birds and shelter for other animals. However too much scrub can alter the special qualities of the remaining fen and the lake margins and it may sometimes be necessary to carry out control manually. The small area of conifer plantation should not be allowed to increase.

Invasive non-native species: Species such as water fern and swamp stonecrop can spread extremely rapidly, due to a lack of natural controls and out-compete native species. If possible, any introductions should be eradicated. Such species are present on Anglesey and can 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 even if not known to have been in contact with any invasive species.

Ruddy duck: The non-native North American ruddy duck is increasing in numbers and migrating to Spain where they are interbreeding with the globally threatened white-headed duck. Necessary control measures for ruddy duck at Llyn Alaw should be managed sensitively to safeguard other wildfowl on the lake. Only non-toxic lead free shot should be used.


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

Llys y Bont,

Ffordd y Parc,

Parc Menai,


Gwynedd, LL57 4BN,

Telephone: 01248 672500