China plunged into a doping crisis at the Rio Olympics today with swimmer Chen Xinyi failing a drugs test. The Chinese Swimming Association confirmed that 18-year-old Chen tested positive for diuretic hydrochlorothiazide on August 7, the day she finished fourth in the 100m butterfly final. Chen has applied to the International Olympic Committee (IOC) for testing of her B sample and a hearing to look into the matter, said the Chinese Swimming Association. “The CSA has taken this matter seriously and demanded full cooperation from Chen in the investigation,” the CSA said. “The CSA resolutely opposes use of banned substances. We will cooperate with the Court of Arbitration of Sport during its investigation and will respect the final ruling by the CAS.” WATCH: golden moments on Day 6 at the Rio Olympics Diuretics increase urination rates and can be used as “masking agents” to hide the presence of performance-enhancing substances that are screened for in doping tests. Chen missed the bronze medal by nine-hundredths of a second. Chen finished sixth in the 100m fly last summer at the world championships in Kazan, and she also won a gold medal for her prelims leg on China’s 400m medley relay at that meet. She won gold at the 2014 Incheon Asian Games in the 50m free, 100m fly and 400m free relay. The positive comes as China vigorously defends its athletes in the face of another drugs storm in Rio, particularly surrounding superstar swimmer Sun Yang. He makes me sick: French swimmer Camille Lacourt casts doubt on China's Olympic Games champion Sun Yang Australian swimmer Mack Horton called Sun a “drug cheat” before and after he beat the controversial Chinese hero in the 400m men’s freestyle final. Accusations and insults have been flying back and forth ever since. Chen becomes the first Chinese athlete to test positive at an Olympics since 1992 in Barcelona. China’s biggest swimming drug scandal came at the 1994 Asian Games in Hiroshima when seven of their team tested positive. A year later, the official Chinese People’s Daily published an anti-doping policy and proclaimed an official prohibition on performance-enhancing substances. At the 1998 World Swimming Championships in Perth, human growth hormone (HGH) was discovered in Chinese swimmer Yuan Yuan’s luggage in a random search at the airport. She had enough HGH to supply the entire women’s swimming team for the championships. Yuan Yuan was banned for four years. Also at the Perth championships, banned diuretic masking agent triamterine was found in the urine of four Chinese swimmers – Wang Luna, Zhang Yi, Cai Huijue and Wang Wei. They were all suspended from competition for two years. Sun Yang war with Australia spills into cyberspace as hacker fans are blamed for taking down country’s first online census Meanwhile, Bulgarian athlete Silvia Danekova confirmed she had failed a doping test, with reports saying she has tested positive for blood booster EPO. “We have found out that my fourth test was positive. The shock for me is unbelievable,” the 33-year-old said.