Whats river was intentionally flooded during world war one?
During World War I the decision was made in October 1914 to flood the land east of the Yser River on the Western Front. The Belgian Army made the decision in order to block the Imperial German Army as they advanced towards the Channel ports of Dunkerque and Calais. They opened the gates at Nieuwpoort to flood the province of West-Flanders. The Germans were unable to fight in the area and the final battle never happened.
The Battle of the Yser was part of the "Race to the Sea", the name given to the mobile warfare on the Western Front.