A small armada of tour boats pulled up at the floating fishing village and a gaggle of foreigners alighted onto the rickety platform that serves as its makeshift town square.

They proceeded to the leaking rowboats and crusty kayaks that lined the pontoon and headed out past the floating junk homes of the locals to explore nearby caves in the limestone islands that give Ha Long Bay its natural skyline and that once ensured its inclusion on UNESCO's World Heritage List.

One wondered if they had all received the same warning before disembarking — namely, not to touch the water. Full of the locals' excrement, the tour boats' effluent and the litter of various parties, this is widely regarded to be fetid and unfit for either consumption or physical contact.

The impact of tourism and economic development on Ha Long Bay, in Vietnam's north-eastern Quang Ninh Province, has long been a cause for concern among environmentalists.

While numerous measures have been put in place over the past couple of years to mitigate these problems — such as the establishment of the Ha Long Bay Alliance, a USAID-funded partnership between Washington and Quang Ninh's People's Committee, and the forced resettlement of several hundred residents from floating villages to the mainland last year — recent events have shown how inadequate these have been.

In July, Quang Ninh experienced its worst floods in 40 years, with run-off from the area's thousands of hectares of open-pit coal mines and coal-fired power plants escaping inadequate holding ponds and running into the bay.

Former Greens leader Bob Brown described the floods as "another coal-based environmental disaster" and "a human tragedy attended by an ecological disaster in the making."

The Vietnam Academy of Science and Technology's Dao Trong Hung said he was "afraid for the biodiversity of the bay" in the wake of the floods.

"The toxins in the water will destroy various kinds of aquatic life," Mr Hung said.

Coal not only contains high levels of sulphur, but also, in some areas, metals such as lead, zinc and mercury.

"Until now, the management board of the bay has not found an efficient solution to eradicate pollution," Mr Hung said.

While the floods have highlighted the area's environmental fragility, Mark Bowyer, who edits the popular South East Asian travel website Rusty Compass, told the ABC that Ha Long Bay was "noticeably grubbier than it was a decade ago", even before the floods occurred.

Hundreds of boats cruise the bay each day and few have proper water and sewage treatment. ( Supplied: Matthew Clayfield )

"The impact of tourism on Ha Long Bay has been enormous," Mr Bowyer said.

"Hundreds of boats cruise the bay each day and few have proper water and sewage treatment. The water is visibly dirty in places and there's lots of rubbish floating around.

"Some of this is tourism-related and some of it is caused by the heavy coal shipping that takes place through the bay."

Mr Bowyer noted that while "hardline measures" have been applied to locals — such as the forced resettlement program — they "seem not to have been applied to the tourism and coal industries" in equal measure.

"I hesitate to swim in the bay these days, which is tragic," he said.

He is not the only one with such misgivings. Forums on travel websites such as TripAdvisor and Lonely Planet often feature discussions about the level of pollution in Ha Long Bay.

Wikitravel's page on the area warns that "you will be told the water is safe for swimming regardless of the fact that ships dump raw human waste into the water and diesel fuel is everywhere. Pregnant women, children or people with weak immune systems should stay out of the water."

Getting in the water a 'big mistake'

Peter, a 59-year-old Australian tourist who visited Ha Long Bay before the floods, said a short dip in the waters around Dau Be Island had concerned him.

"It was a big mistake," he said. "I was only in for a few minutes. I went under and came out, covered in something — I thought it was oil — and smelled really bad. Some of the children on our boat later came out in a rash," he said.

"I wouldn't go back. There are more people than the bay can cope with, and I don't need to add to that. You wonder how long it can sustain that number of visitors."

Mr Bowyer said that Ha Long Bay's environmental problems were indicative of the country as a whole.

The water is visibly dirty in places and there is lots of rubbish floating around. ( Supplied: Matthew Clayfield )

"All over Vietnam, tourism development is in overdrive with little regard for the environment," he said.

"Major beach destinations like Mui Ne, Hoi An, Phu Quoc and Nha Trang have seen very rapid hotel development with little regard for natural or heritage values.

"Both Mui Ne and Hoi An have been hit by severe erosion related to poorly regulated development, which has seen some beaches completely washed away. And travellers are constantly complaining about piles of plastic and other rubbish accumulating around beach destinations as well."

In July, photos of two tourists picking up trash on Cat Ba Beach in Hai Phong City, about 65 kilometres south-west of Ha Long Bay, went viral here, promoting a national discussion about the country's pollution problem.

"I felt really ashamed," Pham Ngoc Long, who took the pictures, told local media.

"Most tourists at the beach are locals, so I guess the trash was left behind by Vietnamese people, not foreigners."

He said he often had to clear litter from beaches like Cat Ba in order to take wedding photographs without trash in the background.

'Disneyland' construction underway

Protest has occasionally proved effective. Plans to build a cable car into Son Doong, a cave near the Laos-Vietnam border, were scrapped earlier this year after protests from conservationists and tourists alike.

But Mr Bowyer said more needed to be done by the government to maintain the pristine beauty of the country's top tourist spots.

"It's difficult for tourists to raise the standards on their own," he said.

The impact of tourism and economic development has long been a cause for concern among environmentalists. ( Supplied: Matthew Clayfield )

"Sure, visitors to Ha Long Bay can ask boat owners for information about their environmental standards and take care of their own rubbish. But nothing other than well-enforced environmental standards can change the current challenges facing the bay."

Vietnam-based conservationist Jake Brunner told the ABC this would be an uphill battle.

"The government is tightening up waste water management rules for cruise boats operating in the bay," he said.

"But most of these are small boats that can't afford to install the necessary technology. Enforcing the law on these boats is politically challenging."

With this week's announcement that construction is soon to begin on Ha Long Ocean Park — a $US267 million amusement park in the Disneyland vein — it is not difficult to see which way the current, and the piles of garbage floating in it, is flowing.