An unexploded 45kg bomb has been towed into deep waters after being found off the NSW coast.
The weapon was found by an unsuspecting fisherman on Lord Howe Island's Elizabeth Reef, with Defence personnel admitting the item could have posed "a significant risk to the general public".
The local angler was visiting the reef, about 550km off the coast of NSW, with his wife and photographed his discovery and reported it to authorities.
Navy divers aboard HMAS Adelaide carefully removed the abandoned explosive by floating it to the surface and towing it further out to sea where it was dropped into 550-metre-deep waters.
"That depth is really safe. It's not going to ever get washed back up onto the reef," senior marine parks officer John Pritchard said.
Australian Clearance Diving Team One search the unexploded ordnance in the vicinity of Elizabeth Reef. Source: AAP
"There's no deep-sea fishing or trawling allowed out there. It's a recreational fishing zone only.
"The chances of that UXO (unexploded ordinance) ever coming back to the surface is negligible."
The origin of the bomb is not known and divers couldn't estimate its age owing to deterioration, a spokesman for Environment Minister Sussan Ley told AAP.
Bombs of that size were used as long ago as World War I, sometimes dropped from aircraft to target submarines.
The minister's spokesman said it had been a "lengthy operation" between the bomb's initial discovery and retrieval, during which time the reef was closed to visitors.
Ms Ley said the fisherman and Navy divers had potentially saved lives and one of Australia's most important reefs.
A view of Elizabeth Reef, part of the Lord Howe Marine Park, from an MRH-90 helicopter. Source: AAP/ Australian Department of Defence
"The device was regarded as live by the Navy and the consequences could have been quite frightening," she said in a statement on Sunday.
"Thankfully the reef's precious ecosystem is safe and most importantly so are future visitors."
Elizabeth Reef is about 160km north of world heritage-listed Lord Howe Island and spans 8.2km by 5.5km.
Along with nearby Middleton Reef, it is the southernmost coral reef platform in the world.
"There's been 125 corals identified there (and) over 300 species of fish," Mr Pritchard said.
"It's quite a unique environment and, because it's so far from anywhere, it's relatively untouched."
