Crymlyn Bog

Crymlyn Bog (Welsh: Cors Crymlyn) is a nature reserve and a designated Site of Special Scientific Interest of international significance, near Swansea, south Wales.

It is the largest area of lowland fen in Wales and lies immediately to the eastern side of Kilvey Hill just north of the industrial area of Crymlyn Burrows.

Plantlife found in the bog is more typical of that found in East Anglia. Habitats range from swamps, carr (fen), water meadows and tall reed beds to waterlogged scrub consisting mainly of willow, where wetter areas merge with woodland. There are a number of plants found in the wetland that are rare in Great Britain. Examples of these include the slender cotton grass and lesser water plantain. In 2003, surveys of Crymlyn Bog, Pant-y-Sais Fen and the inter-connecting wetlands identified the area as one of only three locations in the UK at which the fen raft spider is found. The extent of the population is unknown but the quality of habitat at the site is considered good enough for the population to be stable.

The reserve is a haven for birds. Predatory visitors like the hen harrier, buzzard, hobby and the occasional marsh harrier visit the site regularly. The site provides an important refuge for a range of wetland birds like the bittern, water rail, sedge and reed warblers, bearded tit and grey heron, which can often be seen or heard there.

There is a visitor centre in the bog, which is frequented by nature and bird watching enthusiasts.