As mythological figures the Boeotian river Asopus and the Phliasian river Asopus are much confounded. They are duplicated a second time as supposed mortal kings who gave their names to the corresponding rivers. Indeed, logically, since the children fathered by gods on various daughters of either Boeotian or Phliasian Asopus were mortal in these tales, then the daughters themselves must have been mortal, and therefore either the mother of these daughters (often given as Metope daughter of river Ladon) or their father Asopus must have been mortal, or both of them.
Apollodorus (3.12.6) informs that the river Asopus was a son of Oceanus and Tethys or according to Acusilaus of Poseidon by Pero (otherwise unknown to us) or according to yet others of Zeus by Eurynome, not making it clear whether he knows there is more than one river named Asopus.
Pausanias (9.1.1) cites Plataean tradition that Asopus was ancient king of that region in succession to King Cithaeron who gave his name to the mountain as King Asopus gave his name to the river and that the city of Plataea was named after Plataea daughter of the river Asopus. Pausanias then oddly comments that he thinks that this eponymous Plataea was daughter of King Asopus rather than the river Asopus.
Oroe, a tributary river of Boeotian Asopus is called by Herodotus (9.51.2) and Pausanias (9.4.4) daughter of Asopus. Pausanias says that the Boeotian city of Thespiae was either named from Thespia daughter of Asopus or from Thespius a descendant of Erechtheus who came there from Athens. This Thespius is otherwise unknown to us. Finally Antiope mother of Amphion and Zethus by Zeus is sometimes a daughter of Asopus.
Statius' Thebaid tells of the warrior Hypseus, mortal son of Asopus, who leads the men of Alalcomene, Itone, Midea, Arne, Aulida, Graea, Plataea, Pleteon, and Anthedon. This Hypseus is slain by Capaneus.
Pausanias (1.12.4) writes that during the reign of Aras, the first earth-born king of Sicyonian land, Asopus, said to be son of Poseidon by Celusa (this Celusa otherwise unknown but possibly identical to Pero mentioned above?), discovered for him the river called Asopus and gave it his name. Diodorus Siculus (4,72) similarly presents Asopus (here son of Oceanus and Tethys) as a settler in Phlius and wife of Metope daughter of Ladon, presumably here and elsewhere the Arcadian river Ladon.
Pausanias (2.15.3) mentions his daughter Nemea, eponym for the region of the same name (possibly the mother of Archemorus in Aeschylus' lost play Nemea). Pausanias (5.22.1) and Diodorus Siculus (4.73.1) also mention a daughter Harpina and state that according to the traditions of the Eleans and Phliasians Ares lay with her in the city of Pisa and she bore him Oenomaus who Pausanias says (6.21.6) founded the city of Harpina named after her, not far from the river Harpinates.
Daughters of Asopus (Asopides)
We find first in Pindar's odes (Nem 8.6–12; Is 8.17–23; Paian 6.134–40) the sisters, Aegina and Thebe, here the youngest daughters of Boeotian Asopus by Metope who came from Stymphalia in Arcadia. Both are abducted by Zeus, one carried to the island of Oenone later to be named Aegina and the other to Dirce's water to be queen there.
Corinna, Pindar's contemporary, in a damaged fragment, mentions nine daughters of Boeotian Asopus: Aegina, Thebe, and Plataea abducted by Zeus; Corcyra, Salamis, and Euboea abducted by Poseidon; Sinope and Thespia (who has been dealt with above) abducted by Apollo; and Tanagra abducted by Hermes. Asopus cannot discover what has become of them until the seer Acraephen (otherwise unknown) tells him that Eros and Aphrodite persuaded the four gods to come secretly to his house and steal his nine daughters. He advises Asopus to yield to the immortals and cease grieving since he is father-in-law to gods. This hints that perhaps for Corinna Asopus himself is not a god. Asopus takes Acraephen's advice.
Of these daughters, Thebe, Plataea, Thespia and Tanagra are properly Boeotian; Euboea fits reasonably into the Boeotian sphere; but Salamis and Aegina are regions that would perhaps fit better with the Phliasian Asopus; Korkyra (= Corfu) is definitely Corinthian rather than Boeotian; and Sinope is surely the colony of Sinope on the Black Sea (originally founded from Miletus).
It is notable that tradition as it comes down to us does not record any children arising from a union of gods with Thebe, Plataea, Thespia or Tanagra and only Diodorus (4.72.1) mentions the otherwise unknown sons Phaiax son of Poseidon by Corcyra and Syrus sprung from Apollo by Sinope and that this child of Sinope is opposed by a conflicting tradition that Sinope tricked Zeus, Apollo and Halys and remained a virgin.
Later texts mostly speak of Zeus' abduction of Aegina, presented as a solitary abuction. Asopus is often clearly the Phliasian Asopus (so indicated by Pherecydes) but not always so. Asopus chases after Zeus and his daughter until Zeus turns upon him and strikes him with a thunderbolt, whence ever after Asopus is lame and flows very slowly, a feature ascribed to both the Boeotian and Phliasian Asopus. In these tales Asopus discovers the truth about the abduction from Sisyphus, King of Corinth in return for creating a spring on the Corinthian Acropolis. This spring, according to Pausanias (2.5.1) was behind the temple to Aphrodite and people said its water was the same as that of the spring Peirene, the water in the city flowing from it underground.
Diodorus Siculus (4.72) who, as mentioned, places his Asopus in Phlius, gives him twelve daughters. Diodorus' list omits the Plataea and Boeotia included by Corinna's list of nine daughters. But it introduces Chalcis which was the chief city of Boeotia and may stand for Boeotia. To make up the twelve Diodorus' list also adds Peirene (the famous spring in Corinth), Cleone (possible eponym of a small city of Cleonae on the road from Corinth to Argos according to Pausanias [2.15.1]), Ornia (otherwise totally unknown), and Asopis. But Asopis may mean Asopian and be an epithet for one of the other known daughters. Ovid in his Metamorphoses twice (6.113; 7.615) calls Aegina by the name Asopis. Indeed in his very next section Diodorus brings in Asopus' daughter Harpina who has been discussed above.
Apollodorus (3.12.6) claims Asopus had twenty daughters but he provides no list.
Pausanias (2.5.2) mentionins three supposed daughters of Phliasian Asopus named Corcyra, Aegina, and Thebe according to the Phliasians and further notes that the Thebans insist that this Thebe was daughter of the Boeotian Asopus. He mentions no dispute about the others which suggests that in his day the assignment of Aegina to the Phliasian Asopus was generally admitted.
Pausanias (5.22.1) also describes a group sculpture in the sanctuary of Hippodamia at Olympia donated by the Phliasians. It included Nemea, Zeus seizing Aegina, Harpina, Corcyra, Thebe, and Asopus himself. It seems the Phliasians were very insistent that Thebe belonged to their Asopus.
Sons of Asopus
Both Apollodrus and Diodorus also bring in two sons of Asopus, the first named Ismenus and the second named Pelagon (by Apollodorus) or Pelasgus (by Diodorus). Nothing else has survived about this Pelagon. Of Isemenus, Diodorus states only that he emigrated to Boeotia and settled near the Boeotian river which was afterwards called Ismenus from his name.