There's no denying the magic of Vietnam's Halong Bay. Sailing on a traditional junk at a gentle speed through hauntingly beautiful waters dotted with thousands of limestone pillars is an unforgettable experience.

The bay, in north-east Vietnam, has been high on tourists' must-see lists since 1994 when it was listed as a UNESCO World Heritage site for its spectacular seascape.

But the reality behind the picture-postcard views is worrying. Halong Bay is the most popular tourist destination in Vietnam. Last year, 5.5 million tourists, about half of whom were from overseas, visited the area, according to the Vietnam National Administration of Tourism. Advertisement

Most visitors drive from Hanoi, a 3½-hour journey on roads filled with motorbikes and other vehicles. Thousands of tourist boats ply the waters of the bay, which is bordered to the south and south-east by the Gulf of Tonkin. Many sail to the same places within the bay, so it's difficult to escape other boats.

Sadly, a day trip is no longer enough to experience the beauty of Halong Bay. A longer cruise is needed to reach the more pristine parts of this 1550-square-kilometre bay.

When I visited last month, our boat was surrounded by container vessels waiting for better weather before heading to sea. These ships came from Halong City, a growing centre for coal mining, mineral extraction and shipping.

The beaches near docks and piers are often strewn with rubbish and travel sites have noted complaints from visitors about pollution.

The authorities have taken some action, restricting the number of islands in the bay at which boats can land, so most tourists go to the same islands and caves. But past development, such as electrical wiring in caves or cafes on island beaches, can be unsightly. The bay was nominated as one of seven wonders of nature in November, and since then more international cruise ships have sailed in. In the first five months of this year, about 30,000 cruise ship visitors have come to Halong Bay, a 22 per cent increase on the same period last year, according to the Pattaya Daily News.

The managing director of Sydney-based Travel Indochina, Paul Hole, has been running tours to Vietnam for 19 years. He says 90 per cent of Australian tourists to the country visit Halong Bay.

"Once you get out beyond the craziness of the port, and certainly beyond the day-tripper boats, it's one of the most impressive backdrops to a boat trip anywhere in the world," he says. "It's a reality that directly in that port area, just because of the amount of traffic, there's a bit of detritus in the water there, but once you're out in the bay it's not an issue."

He warns tourists against booking a cruise with rogue boat operators who have fake websites, and says that from November to February fog is common, lowering visibility.

"It's important that the authorities keep focused on protecting the natural heritage and regulations around waste disposal and pollution," Hole says.

An escape from the crowds is still possible - but authorities will have to be careful that Halong Bay doesn't become a victim of its own success.

By Mary O'Brien - The Sydney Morning Herald - August 18, 2012