Tethys

Tethys is the daughter of Uranus and Gaia. She was an archaic Titaness and aquatic sea goddess.

Tethys was both sister and wife of Oceanus, the earth-encircling, fresh-water stream. By him she was the mother of the Potamoi (Rivers), Oceanids (Springs, Streams & Fountains) and Nephelai (Clouds). Tethys was imagined feeding her children's streams by drawing water from Okeanos through subterranean aquifers. Her name was derived from the Greek word têthê, "the nurse" or "grandmother." She is the mother of Amphitrite, and therefore Poseidon's mother-in-law.

The war against the Titans
During the first war against the Titans, Tethys raised Hera as her foster child.