Rio 2016: Chinese swimmer Chen Xinyi becomes the first athlete to fail a drugs test at the Games

A Chinese swimmer has become the first athlete to be caught doping at the Rio Olympics when she failed a drugs test after finishing fourth in the women's 100m butterfly.

Chen Xinyi, 18, tested positive for a banned diuretic substance called hydrochlorothiazide, the Chinese Swimming Association confirmed.

“The CSA has taken this matter seriously and demanded full cooperation from Chen in the investigation,” the Swimming Association said. “The CSA resolutely opposes use of banned substances".

It is not a performance-enhancing drug, but it is a masking agent which can be used to hide other performance-enhancing drugs from testers by lowering their concentration in urine. It is classed by the World Anti-Doping Agency as a "specified substance."

Chen, from Shanghai, was seen as a rising star of the Chinese team after she won gold in the 2014 Asian Games in Incheon, South Korea. She took the test in Rio just after she missed out on a bronze medal in her race by nine hundredths of a second.

Her positive test result means she will be forced to pull out of today's 50m freestyle, which she was also scheduled to compete in today.

Chen’s teammate Wang Shun declined to comment after he won bronze in Thursday’s 200-meter individual medley, saying “I don’t know the details.”

Although Chen is the first casualty of the Games proper, allegations of doping in the pool caused plenty of controversy in the run up to Rio. Seven Russian swimmers were allowed to compete after initially being banned following an enormous anti-doping enquiry, drawing outrage from other swimmers.

The Chinese swimming team has already earned lots of attention for its exuberant characters. Fu Yuanhui gave an adorable interview after qualifying for her backstroke final, while Sun Yang was teased online for his so-called 'shark teeth'.

So it's a shame to see a Chinese swimmer making headlines for an altogether nastier reason.

And it would be even worse if Chen is not the last cheat to be revealed. Recently, the Australian swimmer Mack Horton sensationally claimed that Sun Yang was also a doper, leading to a social media spat.