The Yser (US: /iːˈzɛər/ ee-ZAIR, French: [izɛʁ]; Dutch: IJzer [ˈɛizər]) is a river that rises in French Flanders (the north of France), enters the Belgian province of West Flanders and flows through the Ganzepoot and into the North Sea at the town of Nieuwpoort. During the Battle of the Yser in the First World War, by opening the sluices, part of the polder west of the Yser was flooded with seawater between Nieuwpoort and Diksmuide to provide an obstacle to the advancing German Army and keep westernmost Belgium safe from German occupation. The Yser river itself never overflowed its banks.