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A Chinese fisherman ties his boat alongside a pier on the Chaohu lake, where a pollution-linked algae bloom has reappeared, in Hefei, eastern China's Anhui province on June 4, 2008. Algae blooms are common on many Chinese freshwater lakes and are chiefly caused by untreated sewage containing high concentrations of nitrogen, a main ingredient in detergents and fertilisers, as more than 70 percent of China's waterways and 90 percent of its underground water have been contaminated by pollution.
