Boann/Boand
Irish: BOYN--"cow" or "divine cow"
Modern: "Boyne"

Personification of the River Boyne in Ireland, Boann or Boand is the lover of the Dagda¹ and mother of Oengus mac ind-Og.

The name of her husband changes text to text; in the Dindshenachas, it is Nemed; in "De Gabáil in t-Sída", it is Elcmar, who owns the Brugh.

Legend says that Nechtan had a well of wisdom surrounded by nine hazel-nut trees; the nuts fell into the water and were the source of the wisdom. Only the Nechtan and his three cup-bearers were allowed to draw water from the well. However, one day Boann was curious and drew the water for herself. The well overflowed, and pursued Boann to the sea. The water became a river, and the river was called the Boann, or Boyne. Some legends say that she was turned into a salmon and swam in the river, and that she is the same as the salmon of wisdom.

As the mother of Oengus, she is then identifiable with Modron/Rhiannon in Welsh mythology. Oengus is often identified with Mabon ap Modron, and as such is identifiable with Pryderi. As such, along with the significance of the Newgrange settlement and that she is the wife of the Dagda, she may be a sort of Irish version of the Grail bearer, or at least mother of the Grail hero.

Moreover, the story of the salmon reminds me of how Aphrodite/Venus and her son Eros/Cupid (with whom Oengus is often identified) changed into fish, and became the constellation Pisces. It is doubtful this is relevant, but associations are funny things.

As a river deity, she is similar to (the hypothetical) Danu for the Danube and Sabrina for the Severn.

NOTES:
1. In some sources, she is the wife of Nechtan; others say that the Dagda stole her from Nechtan, while some say that Nechtan and the Dagda are the same person, as the Dagda had several names.