You are hereOilliphéist
In ‘Irish Myths and Legends’ by Ronan Coghlan, we are told that Oilliphéist, is an Irish word meaning ‘dragon’ or ‘great worm’, and that ‘a creature of this sort, hearing that Saint Patrick was coming to drive out its kind, cuts its way through the land, thus forming the River Shannon.’ The Shannon is 224 miles long and the is Ireland's longest river.
There is another part of this tale, that whilst gouging out the Shannon, the Oilliphéist swallowed a drunken piper by the name of O Ruairc (O'Rourke). The piper was probably too drunk to care or be aware of his predicament and continued to play his pipes from inside the beasts stomach. Eventually the Oilliphéist spat him out in order to end his annoyance.