Gweunydd Blaencleddau is a large wetland complex in a shallow south-west valley around the headwaters of the Eastern Cleddau river.

Gweunydd Blaencleddau is situated at the head of the Eastern Cleddau river, 1.67 miles (2.69 km) south-west of Crymych and covers an area of 149.6 hectares (370 acres) of shallow south-west trending valley between 190 m and 275 m above sea-level.

It is a mixture of wet heath and damp grassland and has significant populations of the marsh fritillary (Euphydryas aurinia) and the southern damselfly (Coenagrion mercuriale).

[1][2] A Special Area of Conservation has also been established around this north-eastern tributary of the Eastern Cleddau river.

[3] The site is designated for habitats including calcium-rich springwater-fed fens - Alkaline fens; the southern damselfly (Coenagrion mercuriale); marsh fritillary butterfly Euphydryas (Eurodryas, Hypodryas) aurinia; purple moor-grass meadows - molinia meadows on calcareous, peaty or clayey-silt-laden soils (Molinion caeruleae); wet heathland with cross-leaved heath Rhostiroedd gwlyb - Northern Atlantic wet heaths with Erica tetralix; very wet mires often identified by an unstable 'quaking' surface - transition mires and quaking bogs; and blanket bogs.