Michael Phelps said it is "upsetting" not knowing if he has ever competed in a clean sport ahead of the Olympic Games in Rio de Janeiro.
The Games in Brazil have been heavily overshadowed by a doping scandal, which has seen several Russian athletes banned from the Olympics, which includes essentially their entire track-and-field team.
Phelps revealed his frustration at a lack of solution to doping problems, and he is unsure if he has ever competed in a clean event.
"We've had this problem for how many Olympics now? It seems every time it's something that comes up," Phelps, the most decorated Olympic medallist of all time, said on Wednesday.
"It's sad. That's really what it is. It's really sad that we can't control it, that somebody who is in charge cannot control this.
"We all want clean sports. We want everybody to be on the same playing field.
"I think I can honestly say as well in my career I don't know if I've ever competed in a clean sport, and it's upsetting."
Phelps' long-time coach Bob Bowman echoed the Olympian's statements, saying: "Clearly from a team perspective we are just focused on getting the best performances that we can, regardless of the circumstances.
"But I would have to say from a personal standpoint, it's very concerning to me that our governing bodies have dropped the ball in many ways on this. The system is broken and it has to be fixed."