A FENCE is being put up along the northern coast of Pulau Ubin to act as a deterrent to illegal immigrants coming by sea.

It will reduce the number of possible landing spots on the island, and make it easier for the authorities to intercept illegals, the Police Coast Guard told The Straits Times.

But the plan is getting nature-lovers worried because of the threat they say it could pose to marine and coastal life.

Their concern is that feeding patterns and the movement of wildlife, including animals such as otters which move between land and sea, could be affected.

Pulau Ubin is gazetted as a Nature Area in the Singapore Green Plan, and is a popular haven for those who want to enjoy the outdoors.

But the police said the potential impact of the project on the marine environment has been taken into consideration.

It commissioned a formal study - an environmental impact assessment - which showed 'no negative impact at the final sites chosen'.

Other assessments will be made during and after the construction of the barrier, it said in an e-mail response to Straits Times queries.

Ubin's northern coast, which faces Johor, is a known landing spot for illegals.

Boatmen who ferry visitors to and from the island said they saw at least seven illegals being handcuffed and escorted by the police to mainland Singapore from Ubin last weekend.

Police have set up posts at Changi Jetty to check the identification cards of people getting on or off bumboats shuttling between the island and the mainland.

The police would not disclose the exact location and extent of the area being fenced off. They would say only that 'physical barriers' are being put up 'along remote stretches of our coastline, such as the northern coast of Pulau Ubin'.

A Straits Times team visited the island on Tuesday and saw that metal posts were in place - in the sea and on shore - just after the Outward Bound School and going up along the northern coast to Tanjong Balai.

But as work on the posts was incomplete, it was unclear exactly where the fence will end. This has prompted some concern that Chek Jawa beach could also be affected.

The National Parks Board believes this would be unlikely, however, and had indicated to the police that the barriers should not have a negative impact on the area's ecology.

Chek Jawa is home to a diverse range of marine life, including horseshoe crabs, peacock anemones and cuttlefish.

The Nature Society learnt about the fence after a tip-off from a sailing enthusiast. Conservation committee chairman Ho Hua Chew said the project and any environmental impact assessment 'should have been announced in public' before implementation.

But without knowing the extent of the fencing, it is hard to assess the impact on the environment and wildlife, he said.

'Jungle fowl forage on the beach for food, especially at the beach, where the forest comes close to the water,' he added.

'Dugongs moving along waters of the northern shores could be hit if the fences cut across estuaries, because they sometimes swim close to the river mouths to feed.'