Sport has been compromised and athletes have been let down by a “failed” anti-doping system, former Olympic champion Mack Horton said on Monday following revelations that 23 Chinese swimmers were cleared after failing drug tests before the Tokyo Games. The World Anti-Doping Agency (WADA) confirmed on Saturday that the swimmers tested positive for a banned drug but were cleared by a Chinese investigation that found the athletes were exposed to contamination.

WADA said it accepted China’s finding and declined to appeal it, triggering outrage from leading swimmers and criticism from the U.S. Anti-doping Agency. Australian Horton, who refused to share a world championship podium with Chinese rival Sun Yang in an anti-doping protest, said news of the failed drug tests was “infuriating” for the entire sporting community.

“I feel for the deserving athletes who have missed out on life-changing medal opportunities due to a failed system,” Horton, who won a freestyle gold at the 2016 Rio Olympics, said in comments published by the Sydney Morning Herald. “I feel for the deserving athletes at the centre of this episode. They are victim to a system which has disrespected sport in a bid to manipulate success.”

Late on Sunday, WADA issued a statement saying it stood by its decision after viewing a documentary by German broadcaster ARD on the Chinese drug tests. “We are equally confident that WADA’s independent Intelligence and Investigations Department followed up on all allegations received, which were not corroborated by any evidence; and thus, did not meet (the) threshold to open an investigation,” WADA said in the statement.

WADA called a press conference to address the issue later on Monday (1500 GMT). Elite swimmers, including Britain’s triple Olympic champion Adam Peaty, criticised anti-doping authorities over the weekend and questioned why the failed tests were not made public.

However, veteran Australian coach Denis Cotterell defended China’s swimming programme and said accusations the country was engaged in systemic doping were wide of the mark. “I am happy to say I’m absolutely in support of my swimmers and dispute any suggestion of anything orchestrated,” said Cotterell, who is working with China’s national swim team in the leadup to the Olympics.

He told the Sydney Morning Herald China was adamant about having clean sport. “I feel for the athletes here because of how hard they work now to eliminate the tag that was garnered in the ’90s.”

Chinese swimming was engulfed in several doping scandals during the 1990s, with multiple athletes failing drug tests before and during major championships. Cotterell said he understood if rival swimmers were upset and that the anti-doping process could have been better handled.

“It unfortunately allows that doubt to come out and to surface. I can’t prove anything, I just know the truth,” he added. Media reports said the swimmers tested positive for trimetazidine (TMZ), which is found in heart medication, months before the Tokyo Games started in July, 2021.

Cotterell’s former swimmer Sun, a triple Olympic champion, served a three-month doping ban in 2014 for taking trimetazidine, which he said he took to treat a heart condition. The ban was not made public until after it ended.

Sun, 32, is currently serving a four-year ban for a separate doping offence which is due to expire next month.