Two U.S fighter jets dropped four unarmed bombs onto Australia's Great Barrier Reef Marine Park during a training exercise last week.
Navy officials say the jets were forced to jettison the bombs Tuesday after their mission to a nearby bombing range was called off by controllers who said the range was not clear of hazards.
The Navy says the pilots were low on fuel and could not land with the bombs on board.
It says the four bombs were dropped in water more than 50 meters deep and away from the coral reefs.
The incident occurred on the second day of biennial training between members of the U.S. and Australian militaries.
The Great Barrier Reef Marine Park covers an area of about 345,000 square kilometers off the coast of northeast Australia.