The city of "Aigrefeuille d'Aunis" occupies a depression which in medieval times was a floodplain, formed of marshes and peat conducive to forests composed mainly of trees that prefer a damp environment (alder and ash in particular). The commune is traversed in its entire length from south-west to north-east by the branches of a small stream, the "Virson". This continues its course towards the north-east of the plain of Aunis and swollen by waters of several other streams, becomes a small watercourse in the eponymous village of "Virson" and joined on its left side by the Curé, a small coastal river that flows into the Bay of Aiguillon south of the estuary of the Sèvre.