KREOUSA (or Creusa) was the Okeanid Naiad Nymph of the source of the River Peneios (Peneus), probably somewhere in the Pindos Mountains of Thessalia (Thessaly) (northern Greece). She was the mother of Hypseus, the first Lapith king, by the River-God Peneios.
OKEANOS & GAIA (Pindar Pythian Ode 9)
[1.1] HYPSEUS (by Peneios) (Pindar Pythian Ode 9)
[1.2] HYPSEUS, STILBE (by Peneios) (Diodorus Siculus 4.69.1)
CREU′SA (Kreousa). A daughter of Oceanus and Ge. She was a Naid, and became by Peneius the mother of Hypseus, king of the Lapithae, and of Stilbe. (Pind. Pyth. ix. 30; Diod. iv. 69.)
Source: Dictionary of Greek and Roman Biography and Mythology.
Pindar, Pythian Ode 9 ep1 (trans. Conway) (Greek lyric C5th B.C.) :
"He [Hypseus] was the king of the proud Lapithai, a hero of the seed of the great god Okeanos, child of the second generation, whom in the famous dells of Pindos once the Naias Nymphe, daughter of Gaia (Earth), Kreousa (Creusa) bore, sharing the joys of love with the river-god Peneios (Peneus)."
Diodorus Siculus, Library of History 4. 69. 1 (trans. Oldfather) (Greek historian C1st B.C.) :
"He [the River Peneios, Peneus] lay with the Nymphe named Kreouse (Creusa) and begat as children Hypseus and Stilbe, and with the latter Apollon lay and begat Lapithes and Kentauros (Centaurus)."
- Pindar, Odes - Greek Lyric C5th BC
- Diodorus Siculus, The Library of History - Greek History C1st BC
Other references not currently quoted here: Ovid Amores 3.6.31