What is ‘special’ about Llynnau Y Fali SSSI?

Llynnau Y Fali has 6 special features.

As well as the features listed above, Llynnau Y Fali has other habitats that contribute to the special interest. These include willow carr, unimproved acid grassland, bracken, hedgerows, ditches and small rock outcrops. This diversity of habitats similarly supports a wide range of other species including eleven species of dragonfly and damselfly (including The Hairy Dragonfly (Brachytron pratense) and The Variable Damselfly (Coenagrion pulchelum) and water beetles (Gyrinus spp.) including the rare G. suffriana and the nationally scarce species G. paykulli, and these too are a key component of the special interest of the site. Bittern were last recorded breeding in the mid1980s and still use the site to overwinter. Unless specified below, management of this site should aim to look after these habitats as well as the listed features of interest.

What do we want Llynnau Y Fali to look like?

The site should continue to support a clear-water aquatic plant community characterised by a wide variety of pondweeds while the lakes persist. Reedswamp and fen supporting, amongst other things, marsh fern, while providing suitable habitat for breeding and wintering wildfowl and bittern. The mixture of lakes, ponds, ditches and other water habitats; together with the reedbeds, marshland, scrub and wet grassland, should display the process of natural succession from open water to marshy grassland.

What management is needed on Llynnau Y Fali SSSI and why?

Although Llynnau Y Fali 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 Llynnau Y Fali if they are not properly managed. These are the ones we regard as most important::

Natural succession and siltation: These lakes are shallow and therefore likely to undergo siltation in the coming century. Siltation and the subsequent succession are natural processes that should be allowed. However, excessive siltation due to inappropriate management, such as eutrophication, ploughing, overgrazing or land drainage in the catchment should be curtailed. Livestock should only be allowed limited access to the lake where essential for drinking water, since they can exacerbate sedimentation (and nutrient enrichment). The siltation process will result in swamp and wet woodland communities that will be of interest in their own right, albeit different in nature to the existing lake and swamp. Maintenance of the open water body through dredging would be highly disruptive and inappropriate. Opportunities should be sought for new, replacement freshwater bodies elsewhere in the vicinity to initiate new templates for this natural succession.

Water level: Given the proximity to road, airfield and related facilities, opportunities for raising water levels to extend the wetland are limited. However, the potential for wetland creation within low value habitat on the site may be considered, and adjacent to the site should be encouraged.

Water quality: Excess plant nutrients (notably phosphorus and nitrogen) can have an adverse effect on the lake and its wildlife. It enables growth of a narrower range of competitive plant species at the expense of the diversity of desired species. It may also promote algal “blooms” (particularly by Nitrogen-fixing blue-green algae) which smother natural plant populations and may de-oxygenate the water (leading to fish-kills). In such circumstances a lake can become persistently dominated by algae with the loss of most other plants and animals. Due to the disposal of sewage effluent into Llyn Penrhyn since the 1940s, levels of phosphorus, in particular, are extremely high and remain embedded in lake sediments, continuing to pose a long –term threat to the stability of the lake. All activities which contribute nutrient inputs to the lakes have the potential to exacerbate this problem and should be minimised.

Fish: Fish can alter the balance of lake ecosystems through grazing of plants, predation on zooplankton and invertebrates, competition with other fish, or disturbance of the sediments (leading to turbidity and the mobilisation of nutrients). . Given the precarious balance of these hyper-eutrophic (nutrient enriched) lakes, any alteration in the fish community could lead to catastrophic changes in the ecology of the lakes and loss of their special interest, including their distinctive plant and bird communities. Bottom feeding fish such as bream or tench muddy the water and release nutrients from sediments. Introduction of new fish species or removal of fish, including eels, should be avoided without careful assessment of the consequences.

Water sports: Water based recreation can disturb breeding or wintering birds, and should be avoided at critical times. Water sports may also damage plants and increase turbidity at launching points or through wash-induced wave erosion.

Reedbed management: As well as creating water edge habitat for birds, selective cutting and removal of reed growth can serve to slow down natural succession. Because of this it needs to be balanced with other objectives for the site, and carefully assessed for its impact on other special features.

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 continually improving. 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