Believed to have been established around 1200 AD, Dolgarrog is said to have got its name from a flying dragon called Y Carrog. This mythical beast preyed on livestock and Dol-y-carrog was the favourite meadow on which it swooped down from the heights above to carry off sheep. So serious were the losses that the farmers went on a dragon hunt armed with bows, arrows and spears.
One farmer, Nico Ifan, refused to go, claiming a dream had forewarned him the Carrog would cause his death. His fellow farmers laid a poisoned sheep's carcass on the heights above Eglwysbach across the river. The unsuspecting Carrog seized the bait, was caught and beaten to death.
Nico Ifan then came along to gloat over the dead dragon and cursed and kicked the corpse, whereupon the poisoned barbed wing of the Carrog pierced his leg thus fulfilling the death warning in his dream.
On 2 November 1925, the failure of two dams caused a flood that swamped the village of Dolgarrog, killing 16 people. The disaster was started by the failure of the Eigiau Dam, a gravity dam owned by the Aluminium Corporation. The water released from the reservoir flooded downstream, and overtopped the Coedty Dam, an embankment dam. This dam also subsequently failed, releasing the huge volume of water that flooded Dolgarrog.
Many more villagers could have been killed had they not been in the local theatre watching a film that night.
The disaster at Dolgarrog led the British parliament to pass the Reservoirs (Safety Provisions) Act in 1930 that introduced laws on the safety of reservoirs. This has since been updated, and the current one is the Reservoirs Act, 1975.