Llyn y Fan Fach from Llanddeusant

Llyn y Fan Fach lies in a glacial cirque beneath Bannau Sir Gaer, the Welsh name for the Carmarthen Fans, and Fforest Fawr Geopark names it as the source of the Afon Sawdde. The dam is the part with a paper trail. Cadw listed it at Grade II in 2022, recording that Llanelli Rural District Council obtained an Act of Parliament in 1912 to turn the lake into a reservoir for Llanelli, that work began in 1914 with 175 Irish labourers, and that from September 1916 around 200 conscientious objectors, sent by the Home Office, completed it. The concrete dam raised the water by 10 feet, and Dŵr Cymru Welsh Water now keeps the scheme as a reserve supply.

The legend is older. In the folk tale a young man from Blaen Sawdde, near Llanddeusant, marries a woman who rises from the lake on condition that he never strikes her three times; when he does, she returns to the water, and their sons become the Physicians of Myddfai. It is folklore, not record.

Walking Britain starts from the Llyn y Fan Fach car park, SN 798 238, and follows the track south up the valley, passing the filter beds after a kilometre before turning up the Afon Sychlwch to a path onto the escarpment edge. It then runs along the cliffs to the summit of Picws Du, 749m by Wikipedia’s figure, and over the Bannau Sir Gaer crags, before dropping to the dam and the track back. A route published in The Times describes the Picws Du barrow as Bronze Age and says the Beacons Way splits here into higher and lower paths, the lower being by far the safer choice in bad weather. It also warns that the last stretch of road to the car park is a rough track and names Llangadog as the nearest station.

Walking Britain gives 8.6km, 485m of ascent and about four hours, graded moderate. The loop suits walkers who want a lake and a ridge without the numbers on Pen y Fan, since The Times route says this corner sees far fewer visitors. It is not a walk for anyone uneasy beside sheer drops, because the ridge path runs along the escarpment edge; the track to the dam stops short of that, and the Four Waterfalls Walk near Ystradfellte follows rivers rather than a ridge.