The bomb was found by fishermen on the banks of the River Po, which has all but dried up in the valley's worst drought for 70 years.
Extreme drought has revealed an unexploded World War Two (WW2) bomb in an Italian river.
Italy's military carried out a controlled explosion of the 450-kg bomb on Sunday, which fishermen discovered on 25 July near the northern village of Borgo Virgilio in Lombardy.
The River Po, running through Italy's breadbasket Po Valley, has reached historic lows, amid a near absence of rain and snow melt, alongside soaring temperatures, due to climate change.
"The bomb was found by fishermen on the bank of the River Po due to a decrease in water levels caused by drought," Colonel Marco Nasi said.
Nearly 3,000 people living in the surrounding area were evacuated so the bomb could be dealt with safely.
The area's airspace was shut down, while traffic on nearby railways, roads and the river itself was halted.
"At first, some of the inhabitants said they would not move, but in the last few days, we think we have persuaded everyone," said Borgo Virgilio's mayor, Francesco Aporti.
Bomb disposal engineers removed the fuse from the US-made bomb, which they said contained 240 kg (530 pounds) of explosives.
The bomb squad, escorted by police, transferred the device to a local quarry around 45 km (30 miles) away, where it was detonated.
The drying up of the River Po -- the longest river in Italy -- has caused concern in the region, which produces 40% of Italy's food.
Risotto rice growers in the region warned last week that the extreme conditions could permanently dent production, as toxic saltwater is seeping into the ground.
Italy declared a state of emergency last month for areas surrounding the Po, which is currently at one-tenth of its average water level.
Last week, Giancarlo Mantovani, director of the Po Delta drainage consortium, described the situation in and around the river.
"The vegetation on the riverbanks, amphibians and birds have disappeared, and the whole ecosystem living around a freshwater environment, as we had in this territory, is no longer here," he said.