"Tethys bore to Okeanos the whirling rivers,
Neilos and Alpheios and deep-eddying Eridanos,
Strymon and Maiandros and fair-flowing Istros,
Phasis and Rhesos and Acheloios of the silver swirls,
Nessos, Rhodios, Heptaporos, and Haliakmon,
Grenikos, Aisepos, and divine Simoeis,
Peneios, Hermos, and fair-flowing Kaikos,
great Sangarios, Ladon, and Parthenios,
Euenos, Ardeskos, and divine Skamandros."
A few lines later in the Theogony, after the names of the Oceanids (who were also the daughters of Okeanos and Tethys and therefore the sisters of the river gods) appear, Hesiod continues with this information about the rivers:
"And there are as many tumbling and rushing rivers,
all sons of Okeanos and queenly Tethys.
It is hard for a mortal to recite the names of all,
but those who live by them know each of their names."
Rivers were often personified, and in this capacity river gods often contributed to myth and legend. It was believed, for example, that river gods often selected mortal women to be their mistresses. In this way, river gods fathered many mythical children - indeed, the river Inachus was thought to be the father of the lovely Greek heroine and princess Io.
Who's Who in Classical Mythology