The most decorated swimmer of all time, Michael Phelps, testified before Congress on Tuesday evening about doping in his sport.

Phelps, alongside four-time Olympic gold medalist swimmer Allison Schmitt, criticized the World Anti-Doping Agency, widely known as WADA. Earlier this year, an investigation revealed the organization had allowed 23 Chinese swimmers who had tested positive for banned substances to compete in the Tokyo Games. Two of the athletes brought home gold medals, and eleven of those swimmers are heading back to Paris.