Asterion is a river-god, presumably one of the sons of Oceanus

Oceanus

Oceanus ; , Ōkeanós) was a pseudo-geographical feature in classical antiquity, believed by the ancient Greeks and Romans to be the world-ocean, an enormous river encircling the world....

 and Tethys

Tethys (mythology)

In Greek mythology, Tethys , daughter of Uranus and Gaia was an archaic Titaness and aquatic sea goddess, invoked in classical Greek poetry but not venerated in cult. Tethys was both sister and wife of Oceanus...

. Asterion was one of the three river-gods (the other two being Inachus

Inachus

In Greek mythology, Inachus was a king of Argos after whom a river was called Inachus River, the modern Panitsa that drains the western margin of the Argive plain...

 and Cephisus who awarded the territory of Argolis

Argolis

Argolis is one of the regional units of Greece. It is part of the region of Peloponnese. It is situated in the eastern part of the Peloponnese peninsula.-Geography:...

 to Hera

Hera

Hera was the wife and one of three sisters of Zeus in the Olympian pantheon of Greek mythology and religion. Her chief function was as the goddess of women and marriage. Her counterpart in the religion of ancient Rome was Juno. The cow and the peacock were sacred to her...

 over Poseidon

Poseidon

Poseidon was the god of the sea, and, as "Earth-Shaker," of the earthquakes in Greek mythology. The name of the sea-god Nethuns in Etruscan was adopted in Latin for Neptune in Roman mythology: both were sea gods analogous to Poseidon...

. Poseidon, in anger, made the waters of all three rivers disappear so that they don't flow unless it rains, and are dry in summer.

Asterion had three daughters, Euboea

Euboea (mythology)

Euboea is the name of several women in Greek mythology.#Euboea, a Naiad, daughter of the Boeotian river-god Asopus and of Metope. Poseidon abducted her. The island of Euboea was given her name....

, Prosymn, and Acraea

Acraea

Acraea was a name that had several uses in Greek and Roman mythology.*Acraea was a daughter of the river-god Asterion near Mycenae, who together with her sisters Euboea and Prosymna acted as nurses to Hera...

, who were the nurses of Hera

Hera

Hera was the wife and one of three sisters of Zeus in the Olympian pantheon of Greek mythology and religion. Her chief function was as the goddess of women and marriage. Her counterpart in the religion of ancient Rome was Juno. The cow and the peacock were sacred to her...

.