It's a part of Irish folklore. The mythical Dobhar-chú: a large waterhound resembling both a dog and an otter, which was spotted in several lakes in the west of Ireland.
A headstone in Conwell cemetery in Glenade, Co Leitrim, depicts the Dobhar-chú, and is linked to a tale of a fatal attack on a woman by the creature.
Now scientists have discovered the otter had a formidable relative that was a predator six million years ago. Siamogale melilutra was the size of a wolf and weighed about 50kg.
It also had an unusually powerful bite, which would have allowed it to crush shells or the bones of birds and mammals.
Dr Jack Tseng, from the University of Buffalo, US, who led a study of the prehistoric otter's fossilised skull, said: "We don't know for sure, but we think that this otter was more of a top predator than living species of otters are. Our findings imply that Siamogale could crush much harder and larger prey than any living otter can."