A LANDOWNER who illegally filled a fishpond with concrete and turned it into a container storage park has escaped prosecution. An environmental group yesterday criticised the decision by town planners. They fear planning laws are not being properly enforced. And a source in the Yuen Long District Lands Office said landowners were filling in their ponds because they knew the Planning Department was slow to act and unlikely to punish them. To date no one has been prosecuted for illegal changes to land use which cause land degradation and flooding in the New Territories. This is despite laws being tightened under the 1991 Town Planning Ordinance in the face of heavy opposition from the Heung Yee Kuk, several legislators and the New China News Agency. The World Wide Fund for Nature (WWF) notified the planning department in December 1991 that the pond at Man Yuen Chuen near Fairview Park was being filled in. Almost a year later the owner was told to stop using the site for container storage within three months or face prosecution. No mention was made of the illegal change of land use - nor has he been asked restore the site. The owner agreed to stop using the site as a container park but he is unlikely to face prosecution. A Planning Department spokeswoman said: ''The principal of the enforcement notice is to try to stop that development immediately, but the site formation work was already done. ''There was no point to try to stop it from being done. ''I didn't say we don't prosecute people for filling in fishponds. ''But in this case we don't because the site formation work was already done.'' WWF's conservation officer, Mr Billy Hau Chi-hang, was disappointed action had not been taken on what was a clear-cut case. He expected the owner would start using the area for short-term or overnight container storage once the Planning Department was not looking. Mr Hau said the owner should be made to at least remove the concrete in the pond and plant some trees. Turning the area back into a fishpond is probably not now feasible, he said. A source in the Yuen Long District Lands Office said landowners expected to get approval in future for their changes to the land. The department is reviewing zoning in the northwest New Territories and the source said certain areas near the border - such as Man Yuen Chuen - could be re-zoned as container storage yards. The department spokeswoman said the plans would not be released until later this year, but it was intended to retain agricultural land ''as much as possible''. In-filling can lead to environmental and flooding problems because it reduces the flood storage capacity in the area. But the planning department has not prosecuted anyone for in-filling, only for unauthorised use of the land. The only two cases occurred in Sai Kung and involved landowners who refused to stop storing containers on their sites after they received enforcement notices. They pleaded guilty and were fined $10,000 each.