Marathon swimmer Kyle Lee has opened Australia’s medal tally at the World Aquatics Championships, winning bronze in the men’s 10km.

The men’s race became the first final to be decided at the world championships in Singapore after the women’s 10km event was moved from Tuesday to Wednesday because of water quality concerns.

The two open-water events were also postponed from Wednesday morning to the afternoon at Palawan Beach on Sentosa Island, south of Singapore, again because of the dirty sea water.

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Organisers then said water samples collected on Tuesday afternoon had shown a “significant improvement” and went ahead with Wednesday competition, with the women’s 10km race to follow.

German Florian Wellbrock won his sixth open-water world championship, clocking 1 hour, 59 minutes, 55.50 seconds.

He beat Italian Gregorio Paltrinieri by 3.70 seconds, with Lee 14.80 seconds behind Wellbrock in third place.

The Paris Olympian beat another German, Oliver Klemet, by just 0.1 of a second to finish on the podium.

Nicolas Sloman, who also competed in Paris, finished eighth.

Wellbrock also won the 10km event at the Tokyo Olympics.

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Moesha Johnson, who won silver in the 10km at last year’s Olympics, and fellow Paris competitor Chelsea Gubecka are the Australians in the women’s race on Wednesday.

Other open-water races in Singapore are also set for Friday, Saturday and Sunday.

Water quality was a key issue at last year’s Olympics, with the triathlon and marathon swimming events held in the River Seine.

After a massive project to clean up the river for the Games, heavy rain meant the men’s individual triathlon was postponed by one day. All other events went ahead as scheduled.

Once she competes in her open-water events, Johnson will also contest the 800m and 1500m freestyle in the pool at the worlds.

AAP