Alpheus was recognized in cult and myth as the chief or typical river-god in the Peloponnesus, as was Achelous in northern Greece.
He wrestles with Achelous for Deianeira (" destructive to husband "), daughter of Oeneus, king of Calydon, vanquishes the river god, and breaks off one of his horns, which as a horn of plenty is found as an attribute of Hercules in art.
Such a spot he found at the mouth of the river Achelous, where an island had recently been formed by the alluvial deposit; here he settled and, forgetting his wife Arsinoe, married Callirrhoe, the daughter of the river-god.
Amaltheia gave it to Achelous (her reputed brother), who exchanged it for his own horn which had been broken off in his contest with Heracles for the possession of Deianeira.
According to some authorities the nymph Castalia was the daughter of Achelous; according to others the water of the spring was derived from the Boeotian Cephissus.