There is no evidence that abnormal levels of viruses or bacteria in the water caused rowers competing in Rio de Janeiro at the weekend to fall ill, according to US and international sailing officials.
It was reported that 13 of the 40-member US team fell ill after the world junior championships, a test event for next year's Olympics in Brazil.
US officials confirmed the figure but said that was not unusual in international events and it was too early to blame dirty water.
"It would be easy but irresponsible for us to immediately assume that the rowing course is the main or sole point of exposure that caused the illnesses," Glenn Merry, CEO of USRowing, told Reuters.
Merry added that US rowers often took ill abroad and said the fact that coaches also got sick in Rio was an indication water might not be the problem.
The only athlete who fell into the lagoon and consumed significant amounts of water was not one of those who fell ill, Merry added.
Event organisers said they treated 14 people for diarrhea - eight Americans, and three each from Australia and Britain - and that all were medicated and fit enough to compete.
A spokesperson for Rio2016 said "everything suggests" the diarrhea was caused by familiar travel woes rather than dirty water.
The championships were held at the same lagoon that will be used during South America's first Olympic Games next year.