PARIS -- The Olympic women's 10km marathon swimming event started on schedule Thursday after water quality tests in the Seine river met thresholds.
Defending champion Ana Marcela Cunha of Brazil and swimming rivals in the grueling event dived off a platoon by the Alexandre III bridge at 7:30 a.m. local time and swam furiously toward the Pont de l'Alma.
The race features a 1.67km loop completed six times between the two bridges on the river flowing through the French capital.
Games organizers and World Aquatics earlier said the latest tests from the Seine had been assessed as compliant following a meeting with stakeholders.
French authorities have spent 1.4 billion euros ($1.5 billion) on upgrading the city's sewage systems, promising the river will be clean for residents to swim in by next summer.
However, water quality issues proved a headache for organizers during the triathlon events, with test runs to allow athletes to familiarize themselves with the course canceled and the men's race postponed by 24 hours.
A test session for the marathon swimming went ahead Wednesday after being canceled Tuesday because of concerns over water pollution.
Reuters contributed to this report.