阿凡克是一個生活在康威河亞.阿凡克池沼( 阿凡克 水池 )的大妖怪。他非常強壯，當他在心情不好時，他就會打破了水池讓水流出，制造水災，這給康威山谷人民帶來了很大的災難， 農作物毀于一旦，牛、房子都被水淹沒。人們必須采取措施去阻止阿凡克，可它似乎堅不可摧。山谷的年輕人用每個他們可以利用的武器去攻擊它- 矛、箭和劍 - 但人造武器無法傷害他……

The Afanc is a gigantic monster that lives in Llyn-yr-Afanc (The Afanc Pool) in the River Conwy.

He's so strong that when he's in a bad mood, he breaks the banks of the pool, causing floods that bring disaster to the people of the Vale of Conwy. Crops are ruined, cattle are drowned and houses swamped with water.

Something must be done to stop the Afanc but he seems to be indestructible. The young men of the Vale attack the beast with every weapon available to them - spears, arrows and swords - but no man-made weapon can harm him.

The old men of the Vale hold a meeting and decide that if force won't work, the Afanc must be enticed out of his pool somehow and taken to a lake far away beyond the mountains. They start preparations straight away: strong iron chains are forged, and they send for Hu Gardan and his two long-horned oxen - the strongest oxen in Wales - to come to Betws-y-coed.

The Afanc is very partial to beautiful young women, and a brave girl volunteers to coax the monster out of the water. Finally, they choose the lake that's to be the Afanc's new home - Llyn Ffynon Las (Glaslyn) in the shadow of Snowdon - and their plan is complete.

Hu Gardan, his oxen and a band of men with the chains hide themselves in the trees near the Afanc's pool. The girl sits by the water's edge and calls to the monster. He comes out of the water and, laying his head on the girl's lap, goes to sleep with one clawed hand on her breast.

The Afanc is bound with the chains while he sleeps and the chains are attached to the oxen. When he wakes, furious because he's been tricked, he tears off the girl's breast with his claw and dives back into the water.

Slowly, the Afanc is dragged out of the water, but it takes the strength of Hu Gardan's oxen and every man there to pull him onto the bank. They drag him up the Lledr valley to Dolwyddelan, then north-west over Moel Siabod to the head of the Gwynant valley.

On the way one of the oxen loses an eye - it pops out with the strain of pulling and the tears it sheds form Pwll Llygad yr Ych, (Pool of the Ox's Eye). But the hardest bit is yet to come - finally, the oxen pull the Afanc up to into Cwm Dyli, past Llyn Llydaw to Llyn Ffynnon Las, (Lake of the Blue Fountain).

There the men loosen the Afanc's chains and he plunges straight into the deep blue water. Unable to break its rocky banks he can never escape.