A fuath (plural fuathan; Scottish Gaelic pronunciation: [fuə]) or vough (phonetic transcription), literally meaning "hate" in Scottish Gaelic, designates a class of malevolent Highland Gaelic mythological water spirits, inhabiting the sea, rivers, fresh water, or sea lochs.
As a generic term the fuath can include the beithir (behir), peallaidh and ùruisg. The "fuath" in collected Gaelic folklore is substituted by the term "kelpie" in the English translation and commentary portions of John Francis Campbell's Popular Tales of the West Highlands. More broadly, this name is even given to highland or nature spirits.
Their appearance ranges from covered in shaggy, yellow fur to just having a mane down its back, webbed toes, tails with spikes, and no nose. They are prone to wearing green, whether it be a dress, robe, or kirtle, as it is the colour of faeries.
They sometimes intermarry with human beings (typically the female), whose offspring will share a mane, tail, and/or webbed digits. Their banes include sunlight and cold steel, which will kill them instantly. They grow restless upon crossing a stream.
In "The Brollachan" (Popular Tales II, Tale #37), a fuath is represented as being the mother of the brollachan (or brollichan), as a creature with eyes and a mouth but no shape, and limited ability of speech. When Murray or "Ally" of the mill stoked the fire with fresh peat, it caused severe burns to the brollachan lying there, prompting a fuath who was the brollachan's mother to appear, demanding vengeance for her son. But the misshapen brollachan, when asked about the identity of the culprit, could only answer "me" and "you," and the fuath abandoned. Campbell draws the parallel with the story of the Cyclops, who when attempting to name the man who blinded him could only say that it was "No man" who harmed him, because that was the pseudonym that Ulysses had given.