A water monster found specifically in Welsh folklore tradition. Also known as the Addanc or Abhac, it preyed on unwary travellers. Early references, dating back to the Middle Ages, are vague about its shape and size, but later it came to be described as a giant beaver. The reason for this may be that the name Afanc comes from a local dialect word for beaver. On the river Conway in north Wales there is a whirlpool known as Llyn yr Afanc, and local stories tell of the capture of the monster, which was bound by iron chains and dragged from its home to a lake, Llyn Cwm Ffynnon.

The creature is also associated with Lake Bala, where a version of the Noah's Flood story is told. A man named Dwyfan suspected that the monster was going to cause a flood and built an ark to house all the animals he could find. The flood did indeed come, caused by the thrashing of the Afanc. Dwyfan and his wife Dwyfach were the sole survivors and they founded the British race. This story probably originated in the flash floods for which the area is famous. Later, it was said that the Arthurian hero Peredur (Percival) slew the Afanc in single combat, but stories were still told of it as late as the 19th century.