A Chinese ship that spent nine days stranded on the Great Barrier Reef gouged a three-kilometre (two-mile) scar in the coral that could take decades to recover, a top expert said on Tuesday.

David Wachenfeld, chief scientist at the body overseeing the heritage-listed marine park, said the Shen Neng 1 coal carrier had been grinding against and crushing the reef after it veered off course and smashed into it on April 3.

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Officials have expressed anger over the incident and accused the crew of the ship, which was refloated late on Monday and towed away, of taking an illegal route.

“This is by far the largest ship grounding scar we have seen on the Great Barrier Reef to date,” Wachenfeld told public broadcaster ABC.

“This vessel did not make an impact in one place and rest there and then was pulled off. This scar is more in the region of three kilometres long and up to 250 metres (yards) wide.”

Prime Minister Kevin Rudd called the accident, which also leaked about two tonnes of fuel oil into the pristine seas, an “absolute outrage”.

“It is still an absolute outrage that this vessel could’ve landed on the Great Barrier Reef,” he said. “We will leave no stone unturned when it comes to finding out how that happened.”

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An approaching storm hurried authorities into refloating the 230-metre (750 feet) ship — the length of two football pitches — after nightfall on Monday. They pumped compressed air into its bunkers and pulled it free using tugboats.

Officials said the rescue had been carried out without adding to the initial oil spill, which created a three-kilometre slick.

Divers were due to assess damage to the ship, still carrying 68,000 tonnes of China-bound coal, which has been towed to a nearby island.

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But concern on Tuesday focused on the plight of the reef, which was also left plastered with toxic anti-fouling paint from the ship’s hull.

Divers “have found significant scarring and coral damage. They’ve also found quite a lot of anti-fouling (paint) spread across the reef,” Russell Reichelt, chairman of the marine park authority, told ABC radio.

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“It is a concern because it’s designed to be toxic and stop things growing on ships. We’ve already seen observations where anti-fouling paint that’s been scraped off onto the reef is killing corals in its vicinity.”

Officials have promised to investigate allegations that ships have been taking short-cuts through the world’s biggest reef, which covers 344,000 square kilometres (137,600 square miles) off the east coast and is a major tourist draw.

On Monday, three crew members from another large carrier appeared in court on charges of entering a restricted part of the reef without permission, and were bailed to reappear on Friday.

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Conservationists say the incidents highlight the risk to Australia’s environment posed by rocketing resource exports to Asia, which are fuelling a strong recovery from the global financial crisis.

The reef, which is visible from space and is one of the world’s foremost ecological treasures, has already come under pressure from rising sea temperatures and pollution.