Mainland authorities have accepted responsibility for red tide and say they now plan to stem pollution in the Pearl River Delta. Pollution washing into the river combined with favourable weather bred an explosion of the algae, the National Environmental Protection Agency said. 'The red tide should really be dubbed the Pearl River Delta tide,' agency officials were quoted as saying in the Environment Newspaper. 'It is hard to say who directly caused the problem, but Guangdong discharges more than Hong Kong,' spokesman Tong Yu said. Friends of the Earth estimated 80 per cent of the discharges entering Hong Kong waters via the delta came from the mainland. Last year, only 10 per cent of the 2.9 million tonnes of organic waste discharged by Guangdong was treated, the agency said. All China's offshore waters were high in nutrients because enormous quantities of chemical fertilisers rich in nitrogen and phosphorous were washed into the sea, agency officials said. Friends of the Earth spokesman Plato Yip Kwong-to said it was time for Hong Kong to follow the lead of China, which had admitted some responsibility and pledged to take action. 'They keep insisting the tide was not caused by pollution. Hong Kong should really be liaising with the mainland authorities more,' he said. The National Bureau of Oceanography said it was studying which of the chief causes of algae - land pollution or unplanned aquatic breeding - were more significant. Guangdong authorities claim they are investing heavily in waste water treatment plants. A total of 20 billion yuan (HK$18.7 million) is being poured into a series of 115 projects to clean up rivers, lakes, reservoirs and urban sewage discharges. Pui O and Silvermine Bay beaches have reopened after being closed on Monday due to red tide. But the public is warned not to enter the water at nine other beaches - Cafeteria New and Old, Golden, Kadoorie, Butterfly, Tong Fuk, Cheung Sha Upper and Lower, and Tung Wan.