SYDNEY, Australia -- The emergency release of four bombs into the Great Barrier Reef Marine Park by the United States Navy has angered some Australians, despite assurances on Monday that the unexploded ordnance posed no threat to the World Heritage-listed site's delicate ecosystem.
Two AV-8B Harrier jets launched from the aircraft carrier Bonhomme Richard were meant to drop the unarmed bombs on an island near the reef as part of a live-fire exercise last week, but were forced to release them at sea to avoid damaging several unauthorized vessels that had entered the area, according to the Navy.
The episode occurred July 16 off the coast of the Australian state of Queensland as part of a biennial joint training exercise called Talisman Saber, which involves about 28,000 Australian and American military personnel.
The decision to jettison the bombs was made with the authorization of the Australian Defense Force, a United States Navy spokesman, Cmdr. William Marks, told the Australian Broadcasting Corporation. He said the chosen location, about 62 miles off Australia's northeastern coast, had been selected to minimize damage to the reef.
"The approved area where they could do some of this live training with these 500-pound bombs, it was not safe to drop the bombs. There were civilian boats right below them," he was quoted as saying.
"Their priority was to get to a place which would take the least impact. We believe we did drop in between 50 and 60 meters of water in a place where it is not a hazard to shipping and not a hazard to navigation."
But assurances from both countries' armed forces appear to have done little to placate those angered by the incident, which include Senator Larissa Waters of the Australian Greens Party.
"Is this how we look after our World Heritage area now?" she said to the ABC. "Letting a foreign power drop bombs on it?"
The health of the Great Barrier Reef, which stretches for about 1,800 miles and is often referred to as the world's largest living organism, has become a major concern in recent years as scientists have warned that climate change and population pressures pose threats to its long-term survival.
In May, Unesco warned that the reef could be placed on its list of endangered World Heritage sites unless action were taken to protect it from further erosion.
The extent of damage to the reef or other marine life from the incident remained unclear on Monday. A spokesman for the Great Barrier Reef Marine Park Authority told the Australian Associated Press that it would assist the military in locating the bombs and ensuring that they were safely recovered.
But that is not enough for environmental activists like Graeme Dunstan, who called the incident proof that the military was either unwilling or unable to protect the environment.
"How can they protect the environment and bomb the reef at the same time? Get real," Mr. Dunstan told The Associated Press.
Correction: July 22, 2013, Monday
This article has been revised to reflect the following correction: Because of an editing error, an earlier version of this article reported the wrong date for when the bombs were dropped by the United States Navy. It was July 16, not June 16.
This article originally appeared in The New York Times.