Palmer had been found to have “minute traces of a banned substance” in a sample given at the 2013 World Championships in Barcelona, while two separate drug tests at the same competition had come back negative.

FINA ruled in January 2014 that no further again be required in the case against the Australian, who has repeatedly denied ever knowingly taking a banned substance.

The case has been thrust into the limelight, however, following the WADA ordering FINA to reopen the investigation after the governing body had opted to give the swimmer a warning and reprimand following the positive test for the diuretic and masking agent furosemide.

Palmer, winner of a gold medal at Beijing 2008 as part of the Australian 4x200 metres freestyle relay team, was forced to withdraw from the 2015 World Aquatics Championships in Kazan.

The 25-year-old from Brisbane, though, faced the prospect that the WADA could appeal the verdict to the Court of Arbitration for Sport (CAS) with the threat of being stripped of the World Championships silver medal she won in the 4x200m freestyle in Barcelona two years ago, had she been found guilty.

WADA, however, have opted not to proceed with taking the case further, leaving the swimmer free to aim for the place in the Australian team for next year's Olympics in Rio de Janeiro. 

"I am so relieved this is now over and I can try to put it all behind me,” Palmer told the Australian Associated Press.

"It really has been very difficult to deal with the uncertainty of the situation.

"I am grateful that WADA have confirmed that it will not appeal the FINA Doping Panel's decision and I can continue in my preparations for the Olympic qualifiers next year."

Palmer, a double gold medallist at the 2010 Commonwealth Games in Delhi, winning the 200m freestyle and the 4x200m relay, is now expected to compete at the Australian trials scheduled to take place from April 8 to 15 in Adelaide.