World 25km champion Linsy Heister, of the Netherlands, today withdrew in protest from the longest open water event at the 14th FINA World Championships, to be held on Saturday, while the Dutch called for the 25km event to be cancelled because the water is simply too hot.

Heister's decision was taken after consulting Dutch team medical staff in Shanghai. Heister's coach, former medley ace Marcel Wouda advised his charge not to start this Saturday. 

A source told SwimNews: "He firmly believes that FINA should take responsibility after last year's tragic events in Dubai and cancel the race. There are serious health risks when swimming 5.5 to 6 hours in 30 degrees water."

The 25km for men is due to start at 7am tomorrow, the women's at 7am on Saturday, though a 6am start has also been muted by officials concerned that the race might run into trouble as warmer ambient temperatures kick in towards noon.

The water temperature at Jinshan City Beach outside Shanghai has been a hot topic all week. At 30C today it is inside the newly recommended limit of 31 degrees Celsius (88 Fahrenheit) for open water competition. FINA instituted a major overhaul of safety procedures in open water swimming in the wake of a critical report into the death of Fran Crippen (USA), Crippen, who died in a FINA 10km World Cup event in dreadful conditions under a hot midday sun off the coast of Dubai in the United Arab Emirates last October.

However, among the most serious issues yet to be tackled is one that is still constantly raised by swimmers and coaches: if a few degrees less than that is what is deemed acceptable for pool swimmers racing just 50m, then how is it deemed reasonable to have athletes racing at formidable speed for between 5 and 6 hours in waters more suited to the baby pool at the local leisure centre?

The issue has now claimed a world champion before the racing even starts. Time, say many in the sport, to turn a recommendation that few agree with into a fixed maximum that those who must endure 5-plus hours of toil feel comfortable - and safe - with.