The senseless destruction of a scenic stretch of river on Lantau was, as environment chief Sarah Liao Sau-tung said at the time, a serious crime. Hundreds of tonnes of boulders were illegally removed from the bed of the Tung Chung River. A 300-metre section of the river was virtually destroyed. This appalling example of eco-vandalism, exposed by this newspaper in 2003, shocked the community and prompted public calls for Hong Kong's rivers and streams to be better protected. But it was also important that those responsible for the crime were punished. Otherwise, there would be no deterrent. Yesterday, four of those involved were rightly given stiff sentences. The ringleader, Law Kam-fai, the chairman of the Tung Chung Rural Committee, was jailed for two years and fined $10,000. Three of his accomplices were also sent to prison. The District Court judge has sent a message to others who may be tempted to abuse our city's environment in contravention of the law. But only a fraction of Law's sentence related directly to the destruction of the river. The illegal excavation attracted just a fine. Six months of the jail term was for plotting to steal the boulders. The rest of the sentence was handed down for other offences which included conspiracy to commit fraud, and - most serious of all - to pervert the course of justice. The deterrent effect of the case is therefore limited in terms of its ability to help protect rivers. The prosecution and sentences lay down a marker. But more needs to be done. Many of the natural streams and rivers that help beautify Hong Kong and provide a home for a variety of ecological treasures have - perfectly legally - been subjected to man-made alterations. These are often carried out by the government, usually for flood control purposes. The lining of the river beds with concrete is not a crime - but it does great harm to the natural beauty and ecological value of these stretches of water. An emphasis should now be placed on more environmentally friendly methods of flood control. There is also a case for passing a comprehensive river protection law. This would close loopholes and provide the rivers with greater protection. The government has rejected this suggestion. It should think again. The Tung Chung River has now been restored, with the help of environmental experts. A commendable effort has been made to put things right. But it will take years to recover - if it ever does. Four of the people responsible for this crime have now been prosecuted and punished. Justice has been done. But that should not be the end of the matter. The case raised awareness of the need to protect Hong Kong's streams and rivers. It prompted a strong reaction from the public. Further action should be taken to ensure that such acts of degradation can never occur again.