Yser River

Yser River

River, northern France and Belgium. Rising in northern France, it flows through western Belgium and enters the North Sea near Nieuwpoort after a course of 48 mi (77 km). Its estuary was probably as far inland as Loo into the 10th century, but gradual land reclamation has since reduced it to a narrow tidal creek. During World War I (1914) the German advance toward Calais and the English Channel coast was halted at the river when Nieuwpoort sluices were flooded; this checked the German advance and allowed the Allies to set up an impregnable position.