Royal Navy experts have blown up what was suspected to be a pyrotechnic device on the beach at St Annes.
The object, initially believed to be a bomb, was discovered on Monday half a mile out from the shore.
Lytham Coastguard team members attended the scene and made the object secure.
However, as it was suspected to be a piece of Second World War ordnance, the decision was made to call in specialist bomb disposal workers from the Royal Navy.
A team arrived from Scotland on Tuesday morning.
On assessment the item turned out to be a man overboard marker from the Second World War era.
However as the item was suspected to contained a potential chemical or explosive danger the decision was made to carry out a controlled explosion.