Wikipedia
The Dobhar-chú is a creature of Irish folklore and a cryptid. Dobhar-chú is roughly translated into "water hound." It resembles both a dog and an otter though sometimes is described as a half dog, half fish. It lives in water and has fur with protective properties.
Many sightings have been documented down through the years. Most recently in 2003 Irish artist Sean Corcoran and his wife claim to have witnessed a Dobhar-chú on Omey Island in Connemara, County Galway. In his description the large dark creature made a haunting screech, could swim fast and had orange flipper like feet.
A headstone, found in Conwall cemetery in Glenade, County Leitrim depicts the Dobhar-chú and is related to a tale of an attack on a local woman by the creature. The stone is claimed to be the headstone of a grave of a woman killed by the Dobhar-chú in the 17th century. Her name was supposedly Gráinne. Her husband supposedly heard her scream as she was washing clothes down at Glenade lough, County Leitrim and came to her aid. When he got there she was already dead, with the Dobhar-chú upon her bloody and mutilated body. The man killed the Dobhar-chú, stabbing it in the heart. As it died, it made a whistling noise, and its mate arose from the lough. Its mate chased the man but, after a long and bloody battle, he killed it as well.
Note that dobharchú is a modern Irish word for 'otter'. The modern Irish word for water is 'uisce' although 'dobhar' is also (rarely) used. 'Dobhar' is a much older form and cognates are found in other Celtic languages (e.g. Welsh, 'dwr', water). 'Cú' is 'hound' in Irish (see, for example, ' Cúchulainn', the hound of Culainn).The Dobhar-chú is also known as the "dobarcu", and anglicised as "doyarchu" and "dhuragoo".