The 450-kilogram bomb had been spotted in the Po river near Mantua, some 160 kilometres south-east of Milan, ANSA news agency reported.
According to ANSA, Army specialists removed the detonator from the bomb before moving the device to a cave some 45 kilometres away where it was detonated in a controlled manner.
Some 3,000 residents were evacuated from the area around the site where the bomb was discovered. They began returning to their homes in the afternoon.
