A magnet fisherman recovered an unexploded wartime grenade, closing a historic bridge.
Police were called to Marlow Bridge in Buckinghamshire at about 22:20 BST on Saturday after the man found the explosive in the River Thames.
A Royal Logistics Corps Explosive Ordnance Disposal team removed the device.
The bridge re-opened at approximately 01:30, said a Thames Valley Police spokesman.
A British Army spokesman added: "We always encourage the public to contact us if they find unexpected items of this sort. Better to be safe than sorry."
Marlow Bridge was completed in 1832 and designed by William Tierney Clark, who also designed the Szechenyi Bridge across the Danube in Budapest, Hungary.