The Water Monsters
Every significant lake in Ireland has a monster in it. The péist lives in the deep water and kills whatever comes too close to the shore. Each lake has its own creature, its own name, its own story.
The Caoranach of Lough Derg
The Caoranach — the mother of demons — was a vast scaled serpent with a mouth wide enough to swallow a man whole. She was fast in the water and faster on land than anything her size had any right to be. She had lived in Lough Derg in County Clare since before memory. When Patrick drove the monsters of Ireland into the sea, the Caoranach fought back harder than the rest. She chased him. He ran. She followed him back to the lake and he turned and killed her in the water. The blood she shed turned the lake red. That is what Lough Derg means: the red lake.
The Monster of Lough Ree
A monk named Mochua was crossing Lough Ree on the Shannon in a small boat when the creature surfaced beside him. It had a long neck rising straight out of the water, a wide flat head, and a body large enough to overturn the boat if it chose to. It watched them without moving. They did not move either. Eventually it went back down. Mochua and his companions rowed for the shore without stopping. The lake sits between Roscommon, Westmeath and Longford, and the creature has been reported there across many centuries.
The Ollphéist
The Ollphéist — the great worm — had no legs and moved like an enormous serpent, its body as thick as a house and long enough that its tail was still in the mountains while its head was already at the sea. When Patrick began clearing the monsters from Ireland, the Ollphéist tore through the land trying to escape, its body carving a deep trench through the earth as it went. That trench filled with water. It is the River Shannon — the longest river in Ireland, dug by a monster trying to reach the sea before Patrick could catch it. It made it. It is still out there somewhere in the Atlantic.
Key facts about Péist
- Name: Péist (singular), Péisteanna (plural) — “worm, serpent, monster”
- Type: Supernatural lake and river monsters
- Habitat: The lakes and rivers of Ireland — every major lake has its own creature
- Notable creatures: Caoranach of Lough Derg; monster of Lough Ree; the Ollphéist
- Division: Ancient — known in Ireland for over a thousand years
Link/cite this page
If you use any of the content on this page in your own work, please use the code below to cite this page as the source of the content.
Link will appear as Na Péisteanna: https://irishgodsandgoddesses.net - Irish Gods & Goddesses, March 22, 2026