Ryan Lochte hit out at United States team-mate Michael Phelps after the swimmer was arrested for drink-driving in Baltimore on Tuesday.
Phelps - an 18-time Olympic gold medallist - was charged with driving under the influence of alcohol after police in his hometown clocked him driving 84mph in a 45mph zone.
The American was also charged with excessive speed and crossing double lane lines before later being released.
Phelps issued an apology via his official Twitter account on Tuesday, though that did not stop rival Lochte from condemning his actions.
Speaking to celebrity news website TMZ, five-time Olympic gold medallist Lochte questioned Phelps' decision making.
"I'm not concerned ... he just makes dumb decisions," Lochte said.
"He has so much money to get a driver. I even have a driver. [It] just stinks for the sport of swimming.
"But he will become smarter from this. Luckily he did not hurt himself or someone else."