File updated with FINA comment

Bulgaria's Petar Stoychev and Ana Cunha of Brazil claimed controversial men's and women's world 25km titles at Jinshan City Beach in Shanghai today, both races overshadowed by the withdrawal of world champions and eight others on grounds that the water, at between 30.4C at 5am and 32C by the end of racing, combined with a humid 35C day, produced dangerously hot conditions. 

Of the 14 swimmers who did not finish, 10 were men and four women. Some looking distressed as they retired, while USA Swimming recommended that all its athletes withdraw - and the one who chose to start was chased down and fished out on safety fears during the race.

Last October, Fran Crippen (USA) died in similarly troubling conditions in a FINA 10km off the coast of Dubai. It was the first time an athlete had died under FINA's watch and a subsequent report, highly critical of the way open water was run, recommended the imposition of an upper limit on water temperatures. There is nothing in the FINA rule book as yet, but at 31C, the recommendation from FINA is widely seen as having been set too high, with 25km swimmers allowed to race in waters at least 3C higher, and today 5C higher, than the level deemed acceptable for swimmers covering just 50m in a pool.

Among the women who withdrew from the 25km was the Dutch ace who would have defended the crown, Linsy Heister. She withdrew on medical advice that suggested her health could be endangered by conditions. Six men withdrew from the men's race, including the most successful open water swimmer in the world, Germany's Thomas Lurz. He announced his withdrawal yesterday after winning the 5km.

There were complaints from swimmers and teams who suggested that readings at the dock by the end of the race were as high as 32C and believed that officials should have stopped the race. Both 25km races were brought forward to 6am starts to avoid the worst of the heat of the day.

Stoychev won the 25km in 5 hours, 10:39.8 ahead of Russia's Vladymir Dyatchin, 5:11:15.6, and Csaba Gercsak, of Hungary, in 5:11:18.1. In the women's race, Cunha won in 5:29:22.9, the silver going to Angela Maurer, of Germany, on 5:29:25.0, and Alice Franco, of Italy, on 5:29:30.8. 

Over 25km, swimmers have a guide boat with them, while FINA has instituted important changes since the death of Fran Crippen. Nonetheless, problems remain, particularly when it comes to judging whether races should start or not. 

US officials chased down one of their swimmers and forced her out of the race over safety fears. Officials on a boat shouted to Claire Thompson, 22, to stop swimming, because she looked to be in trouble. She continued to swim, so they pursued her, pulled up alongside her and persuaded her to stop. Reports suggest that she was unhappy about the decision.

Thompson, 22, had ignored team recommendations to skip the six-hour race because of searing heat. Two other American athletes withdrew before the start at the urging of USA Swimming.

"USA Swimming felt it in the best interest of athlete safety that they not compete today. Athlete safety is USA Swimming's top priority," a statement said. The water temperature was "very near to exceeding the recommendations made by the open water commission", it added.

Haley Anderson, who has been ill, and Alex Meyer both scratched from the 25km. It was Meyer who raised the alert over Crippen back in Dubai and then joined in the tragic search for his teammate's body.

At a press conference later in the day, FINA executive director Cornel Marculescu would not accept any criticism, saying: "From the information we have, the 25K race today was a very good race. In general in 25K races you have swimmers pulled out. The race was completed in a perfect manner."

Marculescu added that FINA is working with a university in New Zealand to establish better temperature limits, with the International Olympic Committee sharing costs for the research.

"The target is to be ready by the end of this year and it will be included in the rules for 2012 and the Olympics," he said.

FINA president Dr Julio Maglione added: "All necessary safety measures were taken within the recommended regulations."