PUTRAJAYA - Singapore and Malaysia have to work together to ensure the Johor River can produce sufficient water for both sides, said Prime Minister Lee Hsien Loong on Tuesday (April 9).

PM Lee had told Malaysian Prime Minister Mahathir Mohamad about Singapore's concerns over pollution of the Johor River and its long-term yield during the annual Leaders' Retreat.

Speaking to Singapore media in the afternoon to wrap up his visit, PM Lee said: "It's a serious problem. It's an issue that we've to work at together because if there's not enough water in the Johor River, it's not only a practical problem for both sides - it's also a political problem for both sides."

He noted that some steps have already been taken, citing the Linggiu Dam built in 1991 which created a reservoir that supplements the flow of the Johor River.

"Without that, we'd be in very serious trouble today because it would not be possible for the Malaysians to be drawing water upstream of us at Kota Tinggi and still be able to sustain the operation because the river would have gone dry," he said.

PM Lee added that Malaysia had agreed to build a barrage at Kota Tinggi a few years ago so as to keep out seawater from intruding upstream and affecting Singapore's waterworks.

"That has helped but it's not enough because Johor continues to develop, their population grows, their economy grows. They want more water and we can see the difficulties coming in future and therefore we have to work at it again, which we will," he said.

A joint statement issued by PM Lee and Tun Dr Mahathir after their meeting said the leaders "noted both sides' interest to identify appropriate and timely measures, including schemes, to increase the yield of the Johor River, and to safeguard its environmental conditions and water quality", to the extent required by the 1962 Water Agreement.

PM Lee noted that Singapore and Malaysia have dealt with the immediate issues on two "spiky issues" - over maritime boundaries and airspace.

Both countries have taken steps to address the disputes, including suspending overlapping port limits. Singapore has also withdrawn Instrument Landing System (ILS) procedures at Seletar Airport, while Malaysia has indefinitely suspended its Restricted Area (RA) over Pasir Gudang.

But the problems are by no means completely over, he said, noting that the exercise to delimit maritime boundaries will take some time.

On airspace, Malaysia has said it wants to take back control of the airspace over southern Johor that was delegated to Singapore. Both countries have set up a high-level committee to review the Operational Letter of Agreement between Kuala Lumpur and Singapore Area Control Centres Concerning Singapore Arrivals, Departures and Overflights 1974.

"It's a complicated matter because it involves ICAO (International Civil Aviation Organization), it involves other airlines. It involves a vast amount of civil aviation, there are safety issues too. So those are things to work together with them," PM Lee said.

The review has to be done with a view to ensuring the safety and efficiency of civil aviation, he added.

"We will talk to them and see what adjustments are possible. I think it is not reasonable for us to say we will not talk or we will not listen to your concerns, we have to do that," PM Lee said.

He added that the discussions will take some time.

He also said there remain opportunities to cooperate, because the expansion of civil aviation and passenger traffic has been of tremendous benefit to the whole region.

"So, you need to work together in order to realise that and unless we can provide a system which is safe, efficient, and which will meet the needs of the commercial operators, I think all sides will be losers. So, I think that we have to work together with them at the same time we've got to look after our interests."

On ties between the 4G leaders and their Malaysian counterparts in the Pakatan Harapan administration, PM Lee noted that Singapore ministers are developing links and personal ties with the new ministers.

"It's a process of getting to know one another, picking up the threads and taking the relationship forward which continues whoever is in charge on either side. It's a learning journey but it's also an opportunity to develop relations to go on to the next generation," he said.