Llangorse Lake (Welsh: Llyn Syfaddon, variant: Llyn Syfaddan) is the largest natural lake in South Wales, and is situated in the Brecon Beacons National Park, near to the town of Brecon and the village of Llangors.
The lake is famous for its coarse fishing (particularly pike), watersports, the afanc (nicknamed 'Gorsey') and the only example of a crannog in Wales. Llangorse lake is also one of the most mentioned sites in Welsh folklore. It is a site of international conservation importance.
Due to Llangorse Lake's long history of human activity it has been known by several different names during its history both in the Welsh language and in English, other names include the lake's original Welsh name, Llyn Syfaddon/Syfaddan, and Brycheiniog Mere, (the English name Llangorse Lake is comparatively recent).