Georgia-native Sean Ryan unofficially placed 14th in the men's 10-kilometer open water swim before being disqualified when the official standings were released.
The standings were then changed less than an hour later to reflect that Ryan's disqualification had been lifted.
No explanation was given about why he was disqualified or why the decision was reversed.
Ryan is a McCallie School graduate and a former All-American at the University of Michigan.
He was one of 25 swimmers to qualify for the event. Fellow American and defending world champion Jordan Wilimovsky placed 5th.
The race ended just before 10 a.m.