This paper takes a broad view of the rivers and springs that watered the lands around the Corinthian Gulf and ultimately flowed into it. Gulf shores were inhabited by Achaians, Corinthians, Boiotians, Phokians, Lokrians, and Aitolians, different ethnic groups with diverse interests and influences but united by intervisibility and direct communication along and across the Gulf. While some springs in this watershed—for instance, Peirene, Hippokrene, and Kastalia—became famous, the reputations of the rivers were quite restricted. None is navigable, and few flow through the dry season, but namesakes elsewhere in the Greek world reflect territorial and historical claims and reify ethnic and political relationships. Sources anchored communities and supported agriculture. Rivers and valleys defined territories, and offered routes into the interior. Water-bodies were named, integrated into genealogies, and became actors in mythical narratives. Literature and archaeology reveal evidence for the use of water in ritual at some sites, and sometimes specifically in the worship of water-deities. The Corinthian Gulf watershed thus offers a microcosm of watery phenomena in the ancient world.