 Firouz Rahimi in Switzerland. But it's not only Afghanistan that's proved a challenge for the Olympic organisers. For months, the press has been reporting horror stories about the substandard quality of the water in the Seine, the main river running through Paris. In the next few hours, the city's mayor, Anne Hidalgo, will don her swimming costume and take to the river in an effort to convince everyone that the Seine is clean enough for some swimming events. Hugh Schofield reports.