Ptolemy's Geography (2nd century AD) described a river called Βιργος (Birgu); it could be linked to the Proto-Indo-European *bʰergʰ- "to hide, to protect," referring to Waterford Harbour as a place of refuge.
The name Berbha is believed to derive from the Proto-Celtic *boru- ("boil", "bubble"), and is associated with Borvo, the Celtic god of minerals and spring water. Later spellings include Berba, Birga, Baruwe and Berrowe.
The river's name is attributed to the action of Dian Cecht when he slew three serpents found in the heart of The Morrígan's infant son and threw them into the Barrow, thus causing it to boil.
The earliest recorded name for the river is Berbha, from an AD 996 entry in the Annals of the Four Masters.
- Sloighedh la Domhnall ua Néill co Laighnibh co ros-indir o Bherbha siar go fairrge, & do-bert bóromha mhór lais, & do-rad forbhais for Ghallaibh, & for Laighnibh co cenn da mhíos. As don chur-sin torchair Fionn, mac Goirmghiolla, Dunghal mac Dúnghaile I Riagáin, & Ronán, mac Bruadair, mic Duibhgiolla, & aroile saor-chlanna do Laighnibh amaille friu.
- An army was led by Domnall ua Néill into Leinster; and he plundered from the Berbha eastwards to the sea; and he carried off a great prey of cattle; and he laid siege to the Norsemen and the Leinstermen for two months. On this occasion were slain Fionn, son of Goirmghilla; Dunghal, son of Dunghal Ua Riagain; Ronan, son of Bruadar, son of Duibhghilla, and other nobles of the Leinstermen along with them.
The Barrow historically provided a natural boundary between the kingdoms of Laigin on the eastern shore and Osraige on the western shore.
There was a proverb quoted by Sir John Davies that “whoso lives by west of the Barrow, lives west of the law.”