The Yser is a river that rises in French Flanders, enters the Belgian province of West Flanders and flows through the Ganzepoot and into the North Sea at the town of Nieuwpoort. The source of the Yser is in Buysscheure, in the Nord department of northern France. It flows through Bollezeele, Esquelbecq, and Bambecque. After approximately 30 kilo…The Yser is a river that rises in French Flanders, enters the Belgian province of West Flanders and flows through the Ganzepoot and into the North Sea at the town of Nieuwpoort. The source of the Yser is in Buysscheure, in the Nord department of northern France. It flows through Bollezeele, Esquelbecq, and Bambecque. After approximately 30 kilometres of its 78-kilometre course, it leaves France and enters Belgium. It then flows through Diksmuide and out into the North Sea at Nieuwpoort.