BOMB disposal experts were called in to blow up an unexploded artillery shell at Chesil Beach.
Police introduced a 500-metre cordon - sealing off the visitor centre car park - after the device was found at the water's edge.
A controlled explosion was carried out by a bomb disposal unit from the Royal Navy yesterday morning.
Portland Coastguard was notified of the find after a diver discovered the submerged object, which was wedged into the pebbles, on Monday evening.
Police officers emptied the Chesil Beach Visitor Centre car park and evacuated around 30 fishermen from the area as the cordon was introduced.
A police unit remained at the scene overnight to ensure that the shell, which was four feet long and made of a brass material, was not tampered with.
A Portland Coastguard spokesman said: "It was some form of old artillery shell. Off Chesil such objects get buried and unburied in the water."
The Royal Navy bomb disposal unit arrived at the scene at low tide yesterday, shortly before 6.30am.
Portland Beach Road was not closed but the car park remained cordoned off as experts carried out the detonation at around 8.15am.
A Dorset Police spokesman said the area was fully reopened shortly after.
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