Bomb disposal experts have already had to blow up an incendiary bomb near Cologne and have yet to decide how to deal with a larger bomb spotted lying in 16 inches of water near Koblenz.

River traffic was also disrupted earlier this week after a hand grenade was spotted on the banks of the Rhine near Bonn, and authorities along the course of the river have asked people to report any suspicious objects.

During the Second World War the Rhine saw intensive fighting as German troops used it as a barrier to stem the eastern advance of Allied forces....