The Seudre, whose name comes from the word “ser” (river), more than an estuary, is a shallow, well-shaded arm of the sea whose navigability in ancient times attracted the attention of Greek and Roman sailors.

At least since the seventh century, the salinity of its waters has enabled a combination of salt extraction and extensive pisciculture, or fish farming; since 1228, ponds for cuttlefish were built in the ancient banks of the Seudre, supplying the local monks with both food and ink.

The Seudre is a small 61km-long, coastal river travelling southeast to northwest whose source lies in the Saintonge, near Saint-Genis de Saintonge. The river very gently sweeps (1% on average) parallel to the Gironde Estuary to finally empty out into the Atlantic Ocean opposite the southeast shore of Oleron Island.
Its continental portion (41 km of fresh waters) ends at the sluice gates of Port Riberon's locks at Saujon.

Its maritime section spans some 20km in an 8,000-hectare area made up of coastal swamps and bogs, all fed with salty waters by a dense network of many small channels which once formed ancient salterns. Today almost all these saltworks have been converted into “claires,” as ostreiculture is currently the most important activity by far in this area, and even serves as a mark of quality with the label “Huitres de Marennes-Oleron” (Oysters of Marennes-Oleron).

Aerial photo of the Souhe swamps, upstream of Saujon, bordered to the south-southwest by the River Seudre, and bordered to the north by the Pelard Channel, which bounds the Nieulle Swamp. The chalky limestone spur of the village is quite visible in the centre, encircled by a halo of drained swamps and a geographical checkerboard of ancient salterns, which are themselves bordered on the Seudre side by a mosaic of “claires” and fish ponds.