COUNTRYSIDE COUNCIL FOR WALES
SITE OF SPECIAL SCIENTIFIC INTEREST: CITATION
ANGLESEY LLYN GARREG-LWYD
National Grid Reference: SH315 881
Site Area: 17.7 ha
Llyn Garreg-lwyd is selected as an example of tall fen dominated by common reed Phragmites australis.
This shallow basin mire formed on the site of an old lake has developed on the Gwna green schists of the Mona complex overlain by boulder clay. The fen has a particularly high water table with varying amounts of standing water and extensive mats of floating vegetation. A small stream flows through the mire and into a lake which is dammed at the lower end.
The northern part of this site is dominated almost exclusively by common reed Phragmites australis with few associates. Bottle sedge Carex rostrata is locally dominant in the southern part of the fen with bogbean Menyanthes trifoliata, water horsetail Equisetum fluviatile, unbranched bur-reed Sparganium erectum and yellow flag Iris pseudacorus. Greater spearwort Ranunculus lingua, a locally uncommon species, is abundant in the south of the site. Fen meadow communities with abundant sharp-flowered rush Juncus acutiflorus, meadowsweet Filipendula ulmaria, greater birds-foot trefoil Lotus uliginosus and common marsh-bedstraw Galium palustre, occur on the periphery of the fen.
This wetland is also of ornithological interest supporting a range of breeding birds which includes sedge warbler, reed bunting and reed warbler. Bittern has bred here in the past.