What is "seudre"

The Seudre is a river in the Charente-Maritime département, southwestern France, flowing into the Atlantic Ocean. Its source is near Saint-Genis-de-Saintonge. It flows northwest through Saint-André-de-Lidon, Saujon and La Tremblade. It flows into the Atlantic Ocean near Marennes. The lower course of the Seudre is brackish, and is used for oyster farming.