River-woman
From Tolkien Gateway
The River-woman was a mysterious person - apparently some kind of water-spirit - associated with the Withywindle in the Old Forest. She was the mother of Goldberry, who was for this reason known as the "River-daughter". After Tom Bombadil had been pulled into the river by the swimming Goldberry she swam "back to her mother's house in the deepest hollow".[1]