Rio 2016: Michael Phelps annoyed by doping swimmers

Russia's banned Olympic swimmers - Efimova, Vladimir Morozov and Nikita Lobintsev - regained their Olympic eligibility in the final hour after a controversial ruling by FINA, the world's governing body for swimming, and the Court of Arbitration for Sport.

Efimova, who served a 16-month suspension from 2013-2015 for a positive test for DHEA, a steroid, and again this past March for meldonium, won silver in the 100 metre breaststroke on Monday, much to the chagrin of Team USA captain Phelps.

"It's sad that today in sports in general, not just only swimming, there are people who are testing positive who are allowed back in the sport - and multiple times - it breaks what sport is meant to be and that's what pisses me off," Phelps told reporters after his semi-final swim of the 200m butterfly.

"I believe sport should be clean and sport should be on an even playing field and I think that it's sad that in sports today we have people who are testing positive not only once but twice and still having the opportunity to swim at this Games.

"It breaks my heart and I wish somebody would do something about it."