Beijing (dpa) - Olympic heptathlon silver medallist Lyudmila Blonska of Ukraine has failed a doping test at the Beijing Games, the president of the world governing athletics body IAAF, Lamine Diack, confirmed on Wednesday.

If the b-sample examination confirms the original finding Blonska faces a life-ban as a second-time offender. She will also be stripped of her medal and sent home from the Olympics. Blonska on Tuesday qualified for Thursday's long jump final.

The IAAF announcement cast a cloud over day 11 after Yin Jian of China had won China's first ever sailing gold and Russia had enjoyed success in both open water and synchronized swimming.

"I have just been informed that there has been a positive case. This athlete has tested positive," the IAAF's Diack said at a news conference when asked about the heptathlon silver medallist.

It was not known immediately for which substance the 30-year-old Ukrainian tested positive.

Blonska served a first doping ban 2003-2005 for using the steroid stanozolol and returned to win a world championship silver in 2007.

She finished second at the Olympic heptathlon on Friday and Saturday behind compatriot Natalya Dobrynska and would be stripped of the medal if she has committed an offence.

American champion Hyleas Fountain was third in the heptathlon and Tatiana Chernova of Russia fourth.

The International Olympic Committee said its disciplinary committee will meet on Thursday to discuss the case and then make a recommendation to the executive board for a final ruling.

It is the fifth positive test of the Beijing Games, after the Spanish cyclist Maria Isabel Moreno, North Korean shooter Kim Jong Su, Vietnamese gymnast Do Thi Ngan Thuong and the 2004 Olympic 400m hurdles champion Fani Halkia of Greece.

The first medal of the morning went to Russia when teenager Larisa Ilchenko won the inaugural 10 kilometres open-water swim. South African amputee swimmer Natalie Du Toit finished 16th.

The 19-year-old Russian came from behind to pass the pace-setters Keri-Anne Payne and Cassandra Patten of Great Britain in the closing stages to add gold to eight world titles in the past years.

Du Toit, who lost her lower left leg in a motorcycle accident in 2001, came in just over a minute behind the winner.

Ilchenko clocked 1 hour 59 minutes 27.7 seconds, with Payne beaten by 1.5 seconds in the silver position and Patten taking bronze, 3.3 seconds off the pace at the Shunyi Olympic Rowing-Canoeing Park.

All three medallists paid tribute to the courageous act of Du Toit, who had qualified for Beijing by finishing fourth at the world championships and will also compete at the Paralympics next month in Beijing.

"I find it very hard as an able-bodied athlete, she is an amazing role model. I have utmost respect for her," said Patten.

Payne named Du Toit "an inspiration that you can do whatever you want to do."

Du Toit struck a similar line, saying "I am not a campaigner, I am just realizing my personal dream. There were people who said it is not possible, you set the goal for yourself."

Ilchenko's success was followed by Anastasia Davidova and Anastasia Ermakova's success in the synchronised swimming. They saw off competition from Spanish favourites Andrea Fuentes and Gemma Mengual with Belgians Sara Harada and Emiko Suzuki in third.

There were no morning heats in the Bird's Nest but Jamaican 100m sprint gold medalist Usain Bolt was due to go for his second gold in the 200m at 10.20 pm local time (1420 GMT) in the highlight of the evening's programme.

The women's hammer final and 400m hurdles final will also be contested.