Halirrhothius was a son of Poseidon and the nymph Euryte. He attempted to rape Alcippe, the daughter of Ares, but Ares killed him. (As a result of this, Ares was brought to trial by Poseidon on a hill at Athens that henceforth came to be called the Areopagus, or 'hill of Ares'.)

As we know, Poseidon himself was not overmodest when it came to amatory advancement, and the name of Halirrhothius could be taken as referring to him in this regard, since it means 'roaring with waves', 'sea-beaten', from halirrhothios (hais, halos, 'sea' and rhothos, 'rushing noise as of waves', 'hoarse noise').