Deriving from the Gaelic word murúch (mermaid), the Merrow is the Irish equivalent of the mermaid and mermen of other traditions. These beings are said to appear as human from the waist up but have the body of a fish from the waist down. They are more commonly found on the wilder coasts. Despite their gentle, modest and benevolent disposition, fisherman do not like to see them for they are the sign of a coming gale.

There are other names pertaining to them in Gaelic - Muir-gheilt, Samhghubha, Muidhuachán, and Suire. They would seem to have been around for millennia; according to the bardic chroniclers, when the Milesians first landed on Irish shores, the Suire (sea-nymphs ) played around them on their passage.

Mer-men have been described as being exceptionally ugly with pig-like features and long, pointed teeth. Merrow-maids are extremely beautiful and are promiscuous in their relations with mortals. The Irish merrow differs physically from humans in that her feet are flatter than those of a mortal and her hands have soft white webs between the fingers. It should not be assumed that all merrows are kindly and well-disposed towards mortals. As members of the sidhe, the inhabitants of Tir fo Thoinn (the Land beneath the Waves) have a natural antipathy towards humans. In some parts of Ireland, they are regarded as messengers of doom and death.

Some Merrow-maids are capable of attachment to human beings, and there are reports of them inter-marrying and living among humans for many years; however, they eventually return to their former home beneath the sea. Merrows wear a special red cap called a cohullen druith, usually covered with feathers. If they lose this cap or it is stolen, they lose the power to live beneath the waves. Hiding the cap, a fisherman may persuade the Merrow to marry him. Such brides are often extremely wealthy, with fortunes of gold plundered from shipwrecks. Eventually the Merrow will recover her hat, and with it the urge to return to the sea so strong that she leaves her human husband and children behind.

Merrows are also reputed to lure young men to follow them under the waves where afterwards they live in an enchanted state. She is often seen with a comb parting her long green hair on either side. Sometimes they are said to leave their outer skins behind to assume other more magical and beautiful creatures.

Merrow music can often be heard coming from beneath the waves. An old tract found in the Book of Lecain states that a king of the Fomorians, when sailing over the Ictean sea, had been enchanted by the music of mermaids. When he came within reach of these sirens, they tore his limbs asunder and scattered them on the sea.

From Dr. O'Donovan's Annals of the Four Masters - Entered in the year 887 a.d. there is a curious tale of a Merrow cast on the Scottish coast - Alba. She "was 195 feet in length and had hair 18 feet long, her fingers were 7 feet long as was her nose, while she was as white as a swan." Many coastal dwellers have taken merrows as lovers and a number of famous Irish families claim their descent from such unions, notably the O'Flaherty and O'Sullivan families of Kerry and the MacNamaras of Clare. The Irish poet, W. B. Yeats, reported a further case in his Irish Fairy and Folk Tales: "Near Bantry in the last century, there is said to have been a woman, covered in scales like a fish, who was descended from such a marriage".

Most of the stories are about females, however, there are some about Mer-men who captured the soul of drowned sailors and keep them in cages under the sea.

Sources: O'Hanlon, John - Irish folklore: Traditions and Superstitions of the Country. first published 1870. republished by EP Publishing Ltd., 1973. W.B. Yeats, Fairy and Folk Tales of the Irish Peasantry (1888).