Paris Olympics organisers have cancelled Sunday's swimming training session for the triathlon mixed relay event after recent heavy rain affected water quality levels in the Seine River.
The decision was made late on Saturday after tests showed water quality did not meet the required threshold following rain on 31 July and 1 August.
The mixed relay race is scheduled for Monday.
"We are expecting an improvement on the conditions in the next hours, but not to a level to which the swim familiarisation planned for tomorrow can take place," organisers said in a statement.
"In view of these conditions, we have decided to cancel the swim familiarisation tonight to avoid late communication to athletes."
Pollution in the Seine after heavy rains had caused the men's race to be postponed for a day, after swimming practice sessions were cancelled two days in a row.