Phlegethon, Lethe, and other river gods (presumably)
River Styx, Underworld
Styx was the goddess of the underworld River Styx, one of the Titan generation of Okeanides. She was a firm ally of Zeus in the Titan Wars, who brought her children Nike (Victory), Zelos (Rivalry), Bia (Force) and Kratos (Strength) to stand alongside the god. Zeus rewarded her by making her streams the agent of the binding oath of the gods.
The River Styx was also a corrosive Arkadian stream, which allegedly flowed forth from the underworld. Styx was sometimes identified with several other chthonian goddesses, including Demeter Erinys the wrathful earth, the oath-protecting Eumenides, and Nyx the darkness of night.
Styx was also the personified Daimon (Spirit) of hatred (stygos).
As Styx was also a goddess, she presumably has the following powers:
Possesses the standard powers of a god.
The ability to control his domain, the River Styx.
The ability to control fire, for he was the god of the river of fire.
Heal anyone who drinks from his river (in some legends).
'The river is polluted, for thousands of years, you humans have been throwing in everything as you come across - hopes, dreams, wishes that never came true. Irresponsible waste management, if you ask me