Inachus is the most ancient god or hero of Argos. The river Inachus is said to have received its name from the fact of Inachus throwing himself into it, at the time when Zeus, enraged at the reproaches which Inachus made on account of the treatment of Io, sent a fury to pursue him. (Plut. de Fluv. 18.)
The river had before borne the name of Carmanor or Haliacmon and as Inachus was the first ruler and priest at Argos, the country is frequently called the land of Inachus. (Eurip. Or. 932 ; Dionys. i. 25 ; Hygin. Fab. 143.)
In the dispute between Poseidon and Hera about the possession of Argos, Inachus decided in favour of Hera, and hence it was said that Poseidon deprived him aad the two other judges, Asterion and1 Cephissus, of their water, so that they became dry except in rainy seasons.
The ancients themselves made several attempts to explain the
stories about Inachus: sometimes they looked upon him as a native
of Argos, who after the flood of Deucalion led the Argives from
the mountains into the plains, and confined the waters within
their proper channels; and sometimes they regarded him as an
immigrant who had come across the sea as the leader of an
Egyptian or Libyan colony, and had united the Pelasgians, whom he
found scattered on the banks of the Inachus.