In its latest episode aired Saturday, the reality show asked contestants to dive underwater in the central province and place cement blocks in particular orders on coral reefs.

Completing this task would allow them to find clues to perform their next tasks.

However, the placing of cement blocks on coral reefs, several species of which are listed as endangered, was severely criticized on social media.

“I cannot believe… that people actually set up cement blocks and steel frames on the coral reefs,” said Ngoc Anh Tran, a former participant of the show, in a post on her Facebook page.

“Corals only grow a few centimeters a year; they are [part of] an underwater ecosystem which provides accommodation and food for other creatures… Even if the show’s organizers were not aware of the importance of corals, surely they could not be stupid enough to do such a damaging act to the coral reefs!” she added.

“I condemn the show’s producers for letting such a thing happen; it is a negative image, a negative message that is broadcast by a very popular TV show for young people,” she said, adding that the incident left her “hugely disappointed.”

In response to the backlash, the show’s Facebook fanpage published a post on Sunday, apologizing to viewers and to “the Phu Yen beach.”

The post said the show initially intended for the participants to swim through the coral reefs to reach an area of rocks and sand to find clues, before going back on land to perform their tasks. However, due to a change in water level and its clarity, the organizers decided to move the cement blocks from the rocks and sand area to the coral reefs for clearer footage.

Organizers of the show, which is broadcast on national television, said they have cooperated with third parties to clean up any trash after tasks are performed and warned participants to protect the environment.

“We would like to sincerely apologize to our viewers and the beach of Phu Yen… These things will not happen again,” the post said.

Worldwide, coral reefs have come under growing stress as a result of rising ocean temperatures caused by climate change and other human-induced pressures including overfishing, pollution and tourism.

Coral reefs in shallow waters are among the ecosystems most threatened by climate change and are a key barometer of global warming impacts, scientists say.

“Corals are particularly vulnerable due to the warming of the oceans, rising sea levels, and coral bleaching,” a Reuters report quoted Erick Castro, deputy head of Coralina’s sea and coast division, as saying last November.

Coral bleaching – a whitening driven by temperature changes or other stresses – can kill coral if it is severe enough. Corals are also at risk as oceans become more acidic as they absorb increasing amounts of carbon dioxide in the atmosphere.

Globally, about half a billion people rely on corals for food or to make a living – or for coastal defense, according to the U.S. National Oceanic and Atmospheric Administration.

Prime Minister Nguyen Xuan Phuc has ordered government agencies to study China’s efforts in this area and adopt a similar model. In Beijing, shops and restaurants which open from 8 p.m. to 6 a.m. could receive a subsidy of $70,000, and areas which operate at least 12 hours at night get $700,000.

Nguyen Cong Hoan, deputy director of travel agency HanoiRedtours, told VnExpress International that evening is when tourists spend generously on entertainment and shopping, and therefore a nighttime policy would benefit the country.

“Major cities like Hanoi and Ho Chi Minh City have night markets, but there is demand for more activities. The country needs more restaurants, malls and entertainment areas remaining open after midnight to attract tourists.”

Vietnam has been focusing on nature and cultural tourism, while recreational tourism such as theme parks, shopping centers and late-night shows still have a long way to go, he said.

Hoan pointed out this is why the rate of returning foreign tourists is low compared to countries like Thailand and Singapore. According to the Pacific Asia Travel Association, about 10-40 percent of first-time visitors to Vietnam return, while the rate is 80 percent in Thailand.

“Sightseeing attracts one-time tourists, but shopping and entertainment keep them coming back,” said Hoan.

In China, night catering consumption jumped 47 percent last year from 2017, two percentage points higher than daytime growth, according to Xinhua News Agency.

Nguyen Quoc Ky, CEO of leading tourism firm Vietravel, said revenues from evening services could be much higher than in the day, but most tourism companies are focused on daytime activities, he said.

Apart from markets and backpacker areas, they do not offer tourists many other options at night, according to some tour operators.

Other industry insiders said night clubs, gaming zones and karaoke bars could be revenue spinners at night, and transport services and cross-border financial transactions should also be developed.

But some experts also expressed fears. Economist Ngo Tri Long said a nighttime economy could make drugs and prostitution more commonplace, which is the reason why the country has been reluctant to sanction late-night activities.

Thorough research is needed to see which urban areas are suitable for such policies so that locals’ lives are not affected, he said.

Vietnam’s GDP grew by 6.76 percent in the first half of this year, the highest rate for the period since 2011, according to the General Statistics Office. The Asian Development Bank last week forecast GDP growth of 6.8 percent for the full year, the highest in Southeast Asia.