An ultra-marathon swimmer will test official claims that the Yangtze River's water quality is 'sound' when he attempts to add the mainland's longest river to his list of aquatic conquests. A 50-year-old Slovenian, Martin Strel has swum the 3,004km Danube in Europe, the 3,940km Parana in Argentina and set a world record swimming the 3,797km-long Mississippi River in North America in 2002. On Friday, he will plunge into the Yangtze in southwestern Yunnan and plans to arrive in Shanghai, where it meets the East China Sea, on July 31. 'I chose the Yangtze River because it is a very famous and amazing river. 'It is a symbol of China,' said Strel after arriving in Beijing yesterday. 'I want to set a new world record here.' The Yangtze is the third-longest river in the world and by swimming 50km to 120km per day, Strel hopes to cover 4,200km of the entire 6,300km length in 51 days. Strel will start his record-breaking journey upstream from the famed Tiger Leaping Gorge because the river's upper reaches are too dangerous to navigate in only a wetsuit. On July 16, Strel is scheduled to pass through Wuhan in Hubei province , 48 years to the day since 73-year-old former leader Mao Zedong swam in the same place to prove his fitness. 'I would like to show respect to Mao, who was also an enthusiastic swimmer,' Strel said. 'I hope the activity will promote clean-water awareness in China.' The motto of his record attempt is 'Swimming for peace, friendship and clean waters'. Zhang Shaozhi , director of the Chongqing Municipal Environmental Protection Administration, yesterday said the Yangtze River's water quality had 'remained sound ... since the Three Gorges Dam began to store water a year ago'.