Police put a cordon around the scene on Victoria Road in Walton-le-Dale after a magnet fisher landed an old hand grenade.
Army Disposal officers examined the object before declaring it safe and taking it away to be destroyed.
The road was shut in both directions for more than an hour with traffic diverted around the area.
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The drama began at around 5:30pm when the grenade was fished out from under a bridge.
Police blocked the road at the Yew Tree junction with the A6 London Road and the White Bull roundabout at Church Brow.
A police spokesman told the Lancashire Post the road was shut for public safety precautions until members of the EOD (Explosive Ordnance Disposal) unit arrived to deal with the emergency.
"In the end the grenade was not live and it was taken away," the spokesman told the Lancashire Post.
"It was found by someone magnet fishing."