In the shallow end of Shanghai's largest public pool, amid the crossfire of water fights and volleying beach balls, instructor Xiong Xi, teaches novice swimmers breaststroke basics.
"Kick! Kick! Kick only when I tell you. Kick!" the 57-year-old shouts, holding a girl by her hands for support as she practices frog kicks.
From Chairman Mao Zedong's Yangtze River crossing to the record-shattering Olympic performances at Beijing's Watercube, swimming has long been a symbol of physical strength in China.
Outside the country's elite sports schools, however, competitive swimming is not an option for ordinary Chinese who might want to take it up as a hobby.
Shanghai has poured billions of yuan into hosting this month's world swimming championships, including its new two billion yuan ($309 million) Oriental Sports Centre, as part of efforts to promote the sport.
For most Chinese, however, pools are only a place to cool off, not to race.
"Boiling dumplings" is the popular slang expression for going swimming, because crowded public pools offer so little room that most people simply stand on the spot.
"In China, a swimming pool is really just a place to escape the summer heat. If you really like a sport you do it year round, but very few people do this," said Zhang Yeduan, deputy head of the Hongkou Public Pool, Shanghai's largest.
Regular schools do not have swim teams and there is no network of community swimming clubs so the majority of racing in Chinese pools is at official sport schools, which groom children from a young age to compete internationally.
The swim portion of the 2011 Ironman China in Tianjin was cancelled because no swimming facility was available and eventually the whole event, which had been scheduled for May, was scrapped.
A lack of swimming facilities is the main reason people cannot pursue swimming as a year-round hobby, Zhang said. Many local governments cannot generate enough money from indoor pools to run them year-round.
But the number of facilities is increasing as incomes rise and privately run gyms with pools proliferate, he added.
China does not publish statistics on how many people swim in the country and the China Swimming Association is focused on international competitions, rather than promoting the sport.
Sports school officials also declined AFP's requests for interviews.
But the world championships take place in Shanghai as China's most developed city campaigns to encourage all children to learn how to swim.
For the first time last year, the Shanghai government introduced swimming as an alternative to running for the physical education component on high school entrance exams.
However, only seven percent of Shanghai students chose the swimming option.
China's top university, Peking University, requires all students pass a 200 metre swim test to graduate.
After joining international competitions in the 1980s, Chinese swimming was long overshadowed by doping scandals in the 1990s.
The biggest national dairy recently made a TV commercial starring former Olympian Zhuang Yong, who won China's first swimming medal, a silver, in Seoul in 1988.
And although China has yet to produce any swimming heroes who are as well-known in the country as American Michael Phelps, its national squad is gaining momentum.
After winning just one gold at the 2008 Beijing Olympics, only a year later they finished third on the swimming medals table at the World Championships in Rome.
In the chaos of Hongkou Swimming Pool on a hot July day, instructor Xiong is teaching swimming basics to 12- and 13-year-olds so they can pass the 300-metre test component of the high school exam.
"If you can breaststroke, you can swim," said Xiong, standing in the pool. "Other styles take a long time. Front crawl for example... If kids start by learning front crawl, they will sink once they stop."
The government sees swimming as way of improving children's fitness as China's rapidly growing wealth is also helping fuel childhood obesity.
Mao may have done the most to promote swimming as a fitness test when he swam 15 kilometres (nine miles) across the Yangtze to prove he was still strong enough to lead the Communist Party.
He claimed to have made the crossing in 65 minutes, meaning he would have easily claimed gold in the 10km open water event at the Beijing Olympics, where the men's winning time was close to two hours.
But after his third lesson with Xiong, Xiao Yuli, 13, admitted he was struggling with the breast stroke and would probably choose running for his exam.
"Running is easier, I am not so good at swimming yet," Xiao said.
But his classmate, Yin Yueqin, 12, said she was was becoming a swimming convert.
"I'll choose to swim. My parents said swimming is easier than long-distance running. Through these classes I like swimming more and more," she said.