Corpus of Electronic Texts Edition
The Wooing of Emer by Cú Chulainn (Author: [unknown])

paragraph 36

‘Over the Foam of the Two Steeds of Emain. There was a famous youth reigning over the Gaels. He had two horses reared for him in Sid Eremon of the Tuatha Dea. Nemed, son of Nama, was the name of that king. Then those two horses were let loose from the Sid, and a splendid stream burst after them from the Sid, and there was great foam on that stream, and the foam spread over the land for a great length of time, and was thus to the end of a year, so that hence that water was called Uanub, i.e., foam on the water, and it is Uanub to-day.’