No river in Belgium starts with the letter U.
Beni River
The Yonne is a river in France. The Yser is a river that rises in the north of France and flows into Belgium.
The Meuse River is the major river of Belgium.
dam in a river
The Yser is a river in the County of Flanders, France. The Yser starts in French Flanders, flows into Belgium and into the North Sea.
Avon
Clay.
ural
Wadi
There isn't a river running on the border and separating separating France and Belgium, but there are several rivers flowing from France and into Belgium: Yser, Escaut (called Schelde in Belgium), and the Meuse river.
Ural