Image copyright urgen Freund/WWF-Internation Image caption The world's largest coral reef system is the blessed with breathtaking beauty

Australia faces a dent to its reputation and a potentially devastating blow to its tourism industry should one of the country's most iconic natural wonders, the Great Barrier Reef, be listed as "in danger" by the United Nations.

Tony Fontes loves diving the waters around Queensland's Whitsunday Islands.

In a career spanning three decades, the diving operator has introduced countless others to the magical underworld that is the Great Barrier Reef.

But he has also watched its decline.

Image copyright Bunitj Miles Image caption Divers like Tony Fontes have witnessed a noticeable decline in the reef's health

The waters are now milkier and the coral quality poorer. Increasing attacks by crown-of-thorns starfish have left swathes of reef brown and lifeless.

"There'll always be reef but it's not what it once was," he told the BBC.

Like many others, he is waiting to hear if the reef - which gained World Heritage status in 1981 - will be listed as "in danger" by UN cultural agency Unesco.

The reef is one of more than 1,000 sites on Unesco's World Heritage List considered to be of such outstanding value that the world has an obligation to look after them.

Danger point

Unesco believes the Australian site is worth saving because it contains the world's largest collection of coral reefs, along with 1,500 species of fish and 4,000 types of molluscs.

But it is worried that threats to the reef's health - from overdevelopment, pollution and climate change - have reached a dangerous point.

The reef system has lost 50% of its coral in the past 30 years.

* The Great Barrier Reef includes 3,000 coral reefs and 600 islands

* It is the world's largest marine park

* It receives about two million tourists each year.

* The region contributes A$6bn ($4.6bn; £3bn) a year to the Australian economy

Q&A: World Heritage in Danger List

In pictures: Great Barrier Reef

Late on Friday, Unesco will receive a draft recommendation about whether to place the reef on its "in danger" list. A final decision will be made at a Unesco World Heritage Committee meeting in Germany in late June.

Few expect the international body to take this step - in part because of a flurry of activity by the Australian and Queensland governments to tighten development regulations along the Queensland coast, as well as heavy diplomatic lobbying by the Federal government.

An "in danger" listing would prove problematic for plans to open more coal mines in Queensland and proposals for more coal ports along its coast.

But environmentalists and scientists remain concerned about the reef's long-term fate.

Damage to tourism

Climate change, pollution, coastal development, fishing and dredging for shipping channels have wrought significant damage on the 348,000-sq km World Heritage Site, which stretches from the tip of Queensland to the city of Bundaberg.

There is no question the reef is in danger, says World Wildlife Fund Australia (WWF) marine programme manager, Richard Leck.

"If we'd lost 50% of the Taj Mahal, we wouldn't even question whether it was in danger," he told the BBC, referring to the loss of coral cover.

Image copyright Getty Images Image caption Coral bleaching, invasive starfish and pollution are damaging the reef system

But WWF does not want the reef's heritage status changed.

"We know the impact that will have on Australia's international standing," says Mr Leck.

He says it would deliver a heavy blow to tourism and the coastal communities who rely on it.

Government promises

Submissions to a 2014 Australian parliamentary inquiry into the reef back that view.

As the Whitsunday Charter Boat Industry Association explained: "It has taken a long time to build the brand that is the World Heritage Great Barrier Reef, and making the wrong decision could ruin that reputation."

State and federal governments have taken note of Unesco's scrutiny.

The Queensland government has pledged to forbid new dredge spoil - the sand, silt and rock dug out of the sea floor to create deeper ports - from being dumped in reef waters or on nearby wetlands.

There are also government plans to reduce pollution from fertilisers and pesticides used in coastal farming.

Image copyright Tom Jefferson, Greenpeace Image caption The Abbot Point port near the Reef will service a giant new coal mine in Queensland

Just this week, the Queensland Government announced it would introduce laws limiting port development adjacent to the reef.

The federal government is so worried about a potential listing that officials from its Environment Department have spent A$