Black coal dust washing up on Australian shores near the Great Barrier Reef is making environmentalists nervous.

Complaints have triggered an investigation focusing on nearby coal port Hay Point, which exports tens of millions of tons a year to markets all over the world. However, authorities say they can’t yet confirm whether Hay Point is the source of the leak. Coal dust can directly kill coral and damage sea life, according to scientists, but it’s the burning of coal that indirectly poses the greatest risk to Australia’s most famous heritage site.

Environment Minister Steven Miles summarized the state of the investigation for the Australian Broadcasting Corporation: "That investigation has found one larger and one smaller source of coal spillage," Dr. Miles said.

"But it's not possible yet to say if [Hay Point] is the source of the coal that has washed up on those beaches."

A laboratory will have to test beach coal samples directly to confirm their origin, but Miles is optimistic that this is no Deepwater Horizon disaster.

"The impact on marine life and the reef is likely to be quite localized," he said. "Provided the source can be identified and we can ensure it is not continuing to spill, it is likely to be possible to clean up."

Environmentalists, however, aren’t so sure.

"This is another example of why coal and the Great Barrier Reef don't mix," said Sam Regester, campaigns director for the activist group GetUp!, told Reuters. "We know more ships and more coal equals more accidents."

And more ships are on the way. Hay Point is just one of a number of ports trying to meet China’s surging demand for coal, which has prompted Australia to ramp up its coal production by more than 30 percent between 2008 and 2013.

Conservationists opposed the 2013 opening of another coal port at Abbot Point, just a three-hour drive north of Hay Point, arguing that it would lead to a spike in spills that would jeopardize the reef. Then-Environment Minister Greg Hunt promised that developers would face some of the "strictest conditions in Australian history," but critics countered that it wouldn’t be enough.

"It's hard to dump five-and-a-half million tonnes of mud and sand in the Great Barrier Reef Marine Park without doing massive environmental damage," Greenpeace representative Louise Matthieson told The Christian Science Monitor at the time.

Such predictions may seem prescient today, but it's really a matter of statistics. By 2020, Greenpeace has predicted, the number of coal ships passing through the reef could increase from less than 2,000 to more than 10,000, as the Monitor reported in 2013.

The Great Barrier Reef brings in an estimated $1.5 billion in tourism revenue each year, and the government has promised $1 billion over the next five years to improve the water quality of the reef, but the site remains at risk of falling onto UNESCO's World Heritage Center’s “in-danger” list.

Government scientists classify the reef as having "poor" health, having lost 15 percent of its cover since 2009. Natural causes such as cyclones, floods, and coral-hungry crown-of-thorns starfish shoulder part of the blame, but climate change-inducing emissions are another major cause. As the Monitor's John Zubrzycki wrote:

The world's oceans soak about half of the extra carbon dioxide pumped into the atmosphere by human activities and the more carbon dioxide there is in the water, the harder it is for marine animals like corals to produce their shells. The Great Barrier Reef Marine Authority says "in the long-term, ocean acidification is likely to be the most significant impact of a changing climate on the" reef. Since 1990 alone, the growth rate for one of the reefs major coral species has dropped 14 percent, probably because of rising Co2 levels.

The root of much of that carbon dioxide? Coal. Australia is currently one of the world’s largest per capita CO2 emitters in the world, not to mention the coal that gets exported for burning elsewhere.

Even if the recent leak is found and plugged and not one speck of coal dust makes it into the Australian ocean, just one planned interior mine would produce enough coal to generate 4.73 gigatonnes of carbon dioxide when burned, according to an estimate by the Australian Conservation Foundation.

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“If it goes ahead, burning coal from the Carmichael mine would create billions of tonnes of pollution, making climate change worse and irreversibly damaging the Great Barrier Reef,” the foundation's Josh Meadows told New Scientist.

This report contains materials from Reuters.