Mainland officials may be worrying unnecessarily about the potential impact of the proposed Hong Kong-Zhuhai-Macau bridge on the Pearl River's ecology, professionals and academics said yesterday. But green groups have identified no-go areas with ecological and heritage value where landing points on the Hong Kong side should be avoided. On Wednesday, the Guangdong Governor, Lu Ruihua, said the proposal needed to be studied in detail because of potential ecological problems. He was speaking after meeting Chief Executive Tung Chee-hwa who was on a two-day trip to Guangzhou and Shenzhen, which ended yesterday. The Guangdong side is understood to fear that the bridge proposal could adversely affect the tidal flow in the Pearl River Delta and that cities upstream could face a higher flooding risk. But Raymond Ho Chung-tai, legislator for the engineering sector, said Guangdong was over-worried. 'It is unlikely that the construction of such a bridge would lead to flooding in cities upstream,' he said. Chan Wing-kun, from the Chinese University's geography department, said: 'The exact impact has to be studied. But it seems that the river estuary is so wide that the extent of flow blockage will be minimal.' Professor Chan said road bridges built across the narrower channels upstream might be having a more serious impact on the water flow. But he said more studies needed to be carried out to assess the situation. The Pearl River Estuary covers an area of about 2,000 sq km with a width of between 15 and 35km. The depth is between two to 10 metres while high tide can raise these levels by at least a metre. Hong Kong is still studying the possible landing points for the bridge. In a recent meeting with the environment minister, Sarah Liao Sau-tung, green groups identified several no-go areas in the choice of landing points on western Lantau. They hope that Fun Lau on the southwestern tip of Lantau - where fresh and sea water mixes and which could be turned into a marine park - can be avoided and say the natural coastline from Tai O to Sham Wat should be preserved. Samuel Hung, a researcher on white dolphins at the University of Hong Kong, said he was worried that they would be unavoidably affected if their major habitat near western Lantau was disturbed. Ng Cho-nam, director of the Conservancy Association, said the government should consider expanding the dolphin protection area.