Old Man of the River
The Old Man of the River is a lesser god of the Rhoynar. He is the son of Mother Rhoyne, and his form is that of a giant turtle. According to Rhoynar beliefs, the Old Man of the River fought the Crab King for dominion of all life below the flowing water.
A Feast for Crows
In Dorne, Garin explains the history of the orphans of the Greenblood to Myrcella Baratheon, including their devotion to Mother Rhoyne. When Ser Arys Oakheart says that he had heard the Rhoynar worshipped a turtle god, Garin explains that the Old Man of the River is a lesser god, the child of Mother Rhoyne.