OKYRHOE (or Ocyrhoe) was a Naiad Nymph of Kolkhis (Colchis) at the eastern end of the Black Sea. She was loved by the sun god Helios.

R. E. Bell, Women of Classical Mythology (sourced from Pseudo-Plutarch On Rivers 5) :
"By Helios she was the mother of Phasis. Once after he was grown, Phasis surprised his mother with a lover and killed her. In despair he threw himself into the Arktouros River and drowned. Afterward the river was called the Phasis."

Sources:

• Women of Classical Mythology - English Encyclopedia of Mythology C20th AD

Other references not currently quoted here: Pseudo-Plutarch On Rivers 5