The two AV-8B Harrier jets launched from the amphibious assault ship USS Bonhomme Richard during joint exercises with the Australian military each jettisoned an inert, concrete-filled practice bomb and an unarmed laser-guided explosive bomb into the World Heritage-listed marine park off the coast of Queensland state on Tuesday. None exploded.
The Great Barrier Reef, the world's largest network of coral structures, is rich in marine life and stretches more than 3,000 kilometers (1,800 miles) along Australia's northeast coast.
The Great Barrier Reef Marine Park Authority, the government manager of the 345,400 square kilometer (133,360 square miles) protected marine zone, said in a statement that identifying options for the "rapid recovery" of the bombs so that they could pose no risk to the marine park was "a high priority."
But the authority also said the ordnances posed a "low risk to the marine environment."
"Based on where the ordnance have been dropped in a location that is in water around 50 meters (164 feet) deep, about 30 kilometers (19 miles) from the nearest reef and 50 kilometers (31 miles) from the shoreline, the immediate impact on the marine environment is thought to be negligible," the statement said.
U.S. 7th Fleet spokesman Lt. David Levy said Monday the Navy was currently reviewing the possibility of retrieving the ordnances in consultation with Australian authorities.
"If the park service and the government agencies of Australia determine that they want those recovered, then we will coordinate with them on that recovery process," Levy said in an email.
Levy could not say whether the bombs were damaged or what the effect of long-term immersion in seawater could be.
The four bombs, weighing a total of 900 kilograms (2,000 pounds), were dropped in deep water away from coral to minimize possible damage to the reef, the Navy said.
The jets from the 31st Marine Expeditionary Unit had intended to drop the ordnances on the Townshend Island bombing range, but aborted the mission when controllers reported civilian boats in the way.
The pilots conducted the emergency jettison because they were low on fuel and could not land with their bomb load, the Navy said.
The authority that manages the marine park said the risk of any bomb detonating was "extremely low."
The emergency happened on the second day of the biennial joint training exercise Talisman Saber, which brings together 28,000 U.S. and Australian military personnel over three weeks.
The Navy and Marine Corps were working with Australian authorities to investigate the incident, the Navy said.
Australian Sen. Larissa Waters, the influential Greens party's spokeswoman on the Great Barrier Reef, described the dumping of bombs in such an environmentally sensitive area as "outrageous" and said it should not be allowed.
"Have we gone completely mad?" she told Australian Broadcasting Corp. "Is this how we look after our World Heritage area now? Letting a foreign power drop bombs on it?"