Swimming's governing body FINA has called for virus testing in water which will be used at next year's Olympics, following fears for athletes' health.
Until recently, games organisers insisted viral testing was not necessary, despite an independent five-month analysis by The Associated Press showing dangerously high levels of viruses from human sewage at all Rio Olympic water venues.
The study showed that the spot where athletes will enter the water on Copacabana Beach for marathon swimming and triathlon events had a viral reading that water experts in the United States said would be considered highly alarming if seen on beaches in the US or Europe.
"FINA and its Sports Medicine Committee strongly recommend that viral tests should also be performed," says a FINA letter addressed to games organisers and Rio mayor Eduardo Paes.
"It is very important for FINA that all athletes competing in the marathon swimming event in Rio 2016 Games can compete in an environment free from any bacterial or viral contamination."
FINA said it and Rio state institute INEA are "conducting tests on the water of the Copacabana Beach in order to ensure that during Games time, the athletes will have the best conditions to compete, namely concerning their health and safety".
It was not clear which specific tests FINA and the INEA were conducting.
Games organisers agreed to test for viruses earlier this month after earlier insisting that only bacterial testing was required.