The safety of water pumped into Hong Kong was questioned again yesterday after thousands of dead fish were found floating on the surface of a Shenzhen reservoir which supplies the SAR. Water samples collected at Muk Wo, bordering Hong Kong, showed a sharp increase in ammonia content, up from the usual 0.8mg/litre to yesterday's 1.023mg/litre. The reservoir stores water from Dongjiang, or the East River, before it enters the SAR. Hong Kong spends $2.1 billion a year buying water and 70 per cent of the supply comes from the river. But Ku Chi-chung, assistant director for supply and distribution at the Water Supplies Department, said the level was normal, and insisted ammonia can be diluted by chemical treatment in Hong Kong. He admitted: 'We don't want to see it increase, we wish to keep the level of ammonia as low as possible.' A power failure at a bionitrification plant at the reservoir last Saturday around 4pm was blamed for causing the massive fish death, but environmentalists disputed the explanation. Lister Cheung Lai-ping, general secretary of the Conservancy Association, believed the death of the fish was due to a massive dumping of industrial sewage into the reservoir. 'From the level of ammonia they found in the water sample, I believe it is related to the death of the fish rather than created by the dead fish,' she said. She suggested the ammonia level at the reservoir must be alarming. 'The reservoir is a lively water system, and a normal water system requires no bionitrification plant for oxygen supply,' she said. 'The living things inside can generate oxygen themselves. 'Look at reservoirs in Hong Kong, do we need plants for oxygen supply? No, we don't.' Green Power's chief executive officer Man Chi-sum asked why there was no backup electricity system for the plant. Hugh Phillipson, Director of Water Supplies, reiterated that water was safe for consumption, stressing the water at the reservoir was raw and underwent comprehensive treatment in the SAR before it came out of taps. A spokesman for the Shenzhen reservoir also assured the public the water was not polluted and all the dead fish had been cleared away. The quality of the Dongjiang water has long been criticised. A recent survey by a lobby group, Civil Force, found bacteria levels had increased almost 400-fold in the past six months.