Image caption Catherine Harry says the new design couldn't have come at a worse time for Cambodia

Until recently, video blogger Catherine Harry was a Facebook success story in Cambodia. Her page, A Dose of Cath, featured a series of outspoken first person videos on taboo topics like virginity and menstruation that never got airtime on TV.

Then, on 19 October, Facebook tweaked its News Feed in Cambodia and five other small countries. Instead of seeing posts from Facebook pages in their general News Feed, users in the test had to go to a new section called Explore Feed to see the content. And so when Ms Harry posted a new video on Facebook on Saturday, just 2,000 of her fans saw it in the first hour, compared to about 12,000 who normally watched.

"Suddenly I realised, wow, they actually hold so much power," she said. Facebook "can crush us just like that if they want to".

Ms Harry, who quit her job to focus on vlogging, isn't just worried about her livelihood. Cambodia is in the throes of its most severe government crackdown in years ahead of a national election next July that could test the durability of Prime Minister Hun Sen, one of the longest-serving heads of government in the world.

The crackdown has already claimed two NGOs, more than a dozen radio stations, and the local offices of two independent media outlets, Radio Free Asia and The Cambodia Daily. Hun Sen's main opposition, the Cambodian National Rescue Party (CNRP), could be dissolved entirely at a Supreme Court hearing on 16 November.

"Out of all the countries in the world, why Cambodia?" Ms Harry asks of Facebook's experiment. "This couldn't have come at a worse time."

Facebook surpassed TV as Cambodians' most popular source of news last year, according to a survey from the Asia Foundation, with roughly half of respondents saying they used the social media network.

The platform helped power the CNRP's gains against the governing Cambodian People's Party (CPP) in the 2013 national elections and has been one of the only places for dissent in a country ranked 132nd out of 180 countries in Reporters Without Borders' 2017 World Press Freedom Index.

With most mainstream traditional media aligned with the CPP, Facebook's test could mean that locals only get a skewed version of the day's news, said Von Vorn, a 30-year-old tuk-tuk driver.

"It's like a frog in a pond," he said. "If the frog is in the pond, it won't know anything about the world - just the pond."

Image copyright AFP Image caption The Cambodia Daily newspaper was shut in September amid a tax dispute with the government

Facebook's popularity has not been lost on Hun Sen, who has amassed almost nine million followers with a mix of seaside selfies, state news and singing contests, and whose page was ranked by global public relations firm Burson-Marsteller as the eighth most popular of any world leader.

Hun Sen's longtime rival, Sam Rainsy, the exiled former president of the CNRP who runs a popular page of his own, said his traffic had dipped 20% since the start of the Facebook test. Unlike the prime minister, whom he accused of buying Facebook supporters from foreign "click farms", Mr Rainsy said he could not pay to sponsor his posts to put them in front of more users in their usual News Feeds.

"Facebook's latest initiative would possibly give an even stronger competitive edge to authoritarian and corrupt politicians," he said.

Facebook did not respond to requests for comment. But in a blog post last week, Adam Mosseri, the platform's head of News Feed, said the changes were made "to understand if people prefer to have separate places for personal and public content". The platform had no plans to expand the test globally, he said.

Cambodian publishers of all stripes said they were frustrated by the unannounced changes.

Leang Phannara, web editor for Post Khmer, the Khmer-language version of independent English daily the Phnom Penh Post, said Khmer Facebook posts were reaching 45% fewer people, while web traffic was down 35%. The only way to recapture that audience was to pay to sponsor posts, he said.

"It's a pay-to-play scenario," Mr Phannara said.

Image copyright Getty Images Image caption Sam Rainsy (left) and Hun Sen (right) made a political deal in 2014, but it didn't last

Lim Cheavutha, CEO of the stridently pro-government online outlet Fresh News, was upset by changes he said had eaten into his traffic, though he did not have numbers to hand.

"I absolutely do not support this new [Facebook] policy," he said. "It affects not only my company, but also all other media."

Local non-governmental organisations (NGOs) are also worried about the effect of the move on their marketing efforts, according to Jaime Gill, a local communications consultant.

"Small NGOs have been able to compete by telling really powerful stories about their results," he said. "This experiment has banished those posts to a new feed which I suspect few will use."

'Fake news rampant'

On the streets of Phnom Penh, no one approached by reporters had noticed the change. Sugarcane juice vendor Phorn Phel said he used Facebook to check in on developments across the country and would continue to do so by searching for his usual news sites, which he preferred over state-aligned media.

"We don't want to watch local TV much because there's nothing interesting," he said. "That's why I need to find something on social media instead."

Shop owner Sron Chathou said she spent nearly of all her free time on Facebook but hadn't noticed the experiment. She liked the immediacy of the platform, where her favourite pages would broadcast news like traffic accidents or flooding as they happened.

"We can bring our phone everywhere in our pocket," she said. "No need to wait and see it on TV."

Political analyst Ou Virak said Cambodians' trust in Facebook was misplaced given the rampant amount of fake news and conspiracy theories, often translated from English sources.

"They don't distinguish the source or credibility of information," he said, estimating that seven out of 10 stories that he encountered on his News Feed were false or exaggerated.

Facebook's test, then, was less important than building media literacy.

"I don't see many Cambodians getting real or credible news anyway," he said.

Ben Paviour is a freelance journalist based in Phnom Penh. Additional reporting by Ben Sokhean.