Midges Outbreak at Pandan Reservoir and Long-term Preventive Measures Planned

Ms Foo Mee Har asked the Minister for the Environment and Water Resources (a) what are the interventions used by PUB to counter the current midges outbreak at Pandan Reservoir; (b) how effective have these measures been in controlling the midges population and mitigating its impact to the surrounding living environment; and (c) what additional new measures are being contemplated to help the community affected by the outbreak.

Mr Patrick Tay Teck Guan asked the Minister for the Environment and Water Resources (a) whether there are other water bodies in Singapore experiencing a midges outbreak like that at Pandan Reservoir; and (b) whether PUB is able to predict, prevent and overcome such outbreaks.

Dr Chia Shi-Lu asked the Minister for the Environment and Water Resources regarding the persistent problems created by swarms of midges from Pandan Reservoir (a) what measures are being implemented to reduce the population of these chironomids; and (b) with rising temperatures, whether the Ministry will be considering long-term measures to prevent similar occurrences at this and possibly other reservoirs in the future.

Ms Foo Mee Har asked the Minister for the Environment and Water Resources (a) what expertise and resources does PUB have to understand, monitor and prevent midges outbreaks at reservoirs; (b) what are the key indicators that PUB uses to predict and pre-empt an outbreak; and (c) how can residents living near reservoirs be better protected from the outbreaks.

Thank you. Non-biting midges, also known as chironomids, are a type of flying insect that thrive in water bodies such as ponds, rivers and reservoirs. Midges are part of natural aquatic eco-systems and they are food for fishes and birds.

Midges can multiply very rapidly with each female adult midge laying up to 500 eggs in the water bodies. The eggs take a few days to hatch and become larvae which live at the bottom of the reservoir. After about two weeks, they develop to become pupae, swim to the water surface and emerge as adults. The adult midges live for only one to two days during which time they remain above water bodies to mate and lay eggs to continue their life-cycle.

Midges emergence occurs from time to time in several reservoirs including Pandan, Bedok, Punggol, Serangoon, Poyan, Tengeh and Marina reservoirs, as well as Punggol Waterway. Midge emergence has been known to occur at Pandan Reservoir since the late 1970s. Each emergence can be as brief as two weeks or as long as five months. There are several factors that determine the scale and duration of each emergence including the specific midge species and the environmental conditions such as rainfall, temperature and water chemistry at time of the emergence. We have just experienced a period of hot weather, with July being the second warmest July recorded since 1929. This unusual hot spell hastened the midges' growth process, resulting in the situation at Pandan Reservoir. With climate change, we will experience more extreme weather, which will have a corresponding response from nature.

Midges neither bite nor spread diseases. But they pose a nuisance to the public when they swarm in large numbers and, being weak flyers, get blown by wind into the surrounding residential estates. PUB takes a comprehensive suite of measures to mitigate this nuisance factor as far as is feasible. PUB monitors for midge emergence at reservoirs with known emergence by conducting frequent checks for larvae in samples of reservoir sediments or adult midges trapped around the reservoir vicinity. At Pandan Reservoir, PUB observed an increase in midge larvae since mid-June 2019. PUB kicked in mitigation measures swiftly when the midge emergence began in mid-July 2019.

Similar to what I explained to this House previously in 2016, PUB's mitigation measures for midges include increasing the frequency and dosage of the application of biological liquid larvicide within the reservoir to kill midge larvae; and increasing the frequency of fogging and misting around the reservoir dyke and surrounding vegetation to kill adult midges. These methods have been proven to kill midges at the relevant stages of their life cycle. PUB has also installed bright spotlights at the Pandan Reservoir pumping station and turns them on at night to attract the adult midges as they emerge from the reservoir. By keeping the midges within the reservoir area, PUB can then carry out targeted and effective measures such as fogging at these spots.

Unlike the midge emergence at Pandan Reservoir in 2016, the current dominant midge species is considered a rare one that has not been studied in great detail. This species exhibits different behaviours from other species. For example, they hide in drains and culverts in the day and swarm above the drains in the evening.

PUB has adapted by adding to the usual suite of measures. They have greased the drain walls to trap the midges when they land to rest and have targeted these areas for fogging. PUB has explored the use of free-moving oily paper within drains to increase the capture rates of adult midges, which have worked very well according to feedback from residents. PUB has also extended the existing 0.5 km of netting on the reservoir dyke by an additional 1 km. This netting acts as a barrier to trap adult midges and reduces the number of adult midges that would otherwise be blown to the residential estate.

PUB has worked closely with West Coast Town Council to engage affected residents through multiple channels such as dialogues, daily walkabouts and distribution of flyers and has advised affected residents on the actions they can take within their premises, such as, switching off their lights when not in use, as midges are attracted to light, as well as installing insect screens at their windows or drawing their curtains, if necessary.

But at the end of the day, we have to recognise that man cannot control nature. Midges cannot be eradicated as they are part of the natural aquatic ecosystem and will emerge to breed, especially when aided by favourable environmental conditions. Climate change, as mentioned, will further complicate our efforts.

Our reservoirs supply drinking water to the population and we have to be careful to ensure that – and this is important – PUB's mitigation measures, both short- and long-term, do not end up compromising water quality. However, PUB remains committed to working with the Town Councils and advisors to minimise public inconvenience caused. While PUB will continue to find more effective mitigation measures, we also seek residents' understanding and tolerance, should they find these insects in their homes.

I thank the Minister for his response. Before I raise my supplementary questions to the Minister, I would like to thank PUB and Town Council teams for the very very hard work in tackling the mass midge outbreak. Speaker, since July this year, residents living near Pandan Reservoir, have suffered greatly from the mass emergence of midges. Their homes have been invaded by the midges. Corridors, lifts and bus stops have been swamped. Cars, buses, bicycles and motorbikes have been affected. The midges stick to our clothes, really stick to your clothes, your hair, fly around your eyes, get into your nose, get into your food and they are everywhere.

This year's outbreak is the most severe we have had witnessed yet and also persisted for the longest time impacting the daily lives of our residents. Some of likened it to being in a horror movie. Seriously, if you have visited, it is really scary. I thank residents who took time to join the dialogue sessions we have organised with PUB on the midge issues, there are some really great ideas that have been shared and I would like to raise some for the Minister's consideration in my supplementary questions.

Speaker, I have four supplementary questions. First, whilst I appreciate that fogging has been proven to be an effective way to kill adult midges, there are concerns among our residents about the health risk from exposure to chemicals from sustained fogging, particularly, as the outbreak has lasted for an extended period. I would like to ask the Minister if PUB can find more effective fogging method to target midges at the reservoir as they emerge and keep them away from residential areas.

Second, as the Minister shared, the midges issue cannot be solved or eradicated permanently. I would like to ask the Minister, how can residents be supported with insect screens for their flats as installations of such features are costly as well as other methods that PUB would consider to protect HDB flats and bus stops from the nuisance of midges?

Third, the most effective way to deal with midges is to eliminate them at source. I know PUB uses biological larvicide, BTI, and using tonnes of it this time, at the reservoir, by injecting the larvicide into the reservoir's sediment. But, you know, despite all that, the problem appears to persists. I get constant questions, that I would like to ask the Minister, how PUB determines the effectiveness of BTI in controlling larva population at the reservoir. How can the injected BTI be expected to zero in on the midge larva given the vast area of the reservoir sediment?

Fourth, besides installing nets at the reservoir to serve as barriers to midges flying towards the housing estate, I would like to ask if more trees and shrubs can be added to also serve as barriers and places for the midges to congregate, so that they do not go into people's homes.

I thank the Member for the questions. I think this is a great opportunity for us to go back to our biology lessons. Like I mentioned before, this problem is really man versus nature – the kind of war man has never been known to win. Indeed, we can only suppress, we can only do our best, but we have to live with nature. In fact, we are the ones, who are intruding into their living spaces.

Specific answers to the question on fogging. The pesticide we use is called Permethrin. This particular pesticide that we use in fogging has undergone WHO's pesticide evaluation scheme and has been certified safe and suitable for use. In addition to using a safe pesticide, we also dilute it, dilute it a lot, so that, in addition to just thinking about killing these pests, we also do not want to harm the workers who are using them. So, they are used in a way, in a frequency that is known and recommended by WHO – safe for human, safe for the operators, as well as for the people that we are trying to help.

Secondly, on the insect screens, I think this issue of what you do to help yourself in your home has been well understood. Once you own your property, you own your home, you have to do what you can to protect yourself. Sometimes, we have residents who came to get help, for example, on their leaking pipes or issues which are more pertinent to their own home living conditions. Technically speaking, they should be taking care of these issues, but I think there is no harm, we can see what we can do to help, certainly, from the advisors themselves. We can come together and look at what we can do, because, this situation does not come all the time, not every year. So, to put in something which would become a permanent fixture, this may also affect the kind of image that the reservoir or the places around the reservoir should be. So, I think we have to be very careful about the kind of solutions we want to implement with or for them.

On BTI, the larvicide that we use to put into the water is a safe biological larvicide. It is actually a naturally occurring bacteria – soil bacteria – which produces spores, which are toxic, specifically to the digestive system of midge larvae. As we put in the larvicide, we also monitor the quality of the water. We cannot put so much to kill, just because there are more midges in the river. In the end, the quality of the water gets compromised. So, there is a trade-off between killing enough, or killing too much and we end up killing ourselves. We cannot do that either. There is a limit to which these measures can mitigate the issues that residents are facing.

Finally, on trees and shrubs, we can work with NParks to see first, whether these are actually effective ways to prevent the midges coming in. It is a more beautiful way, definitely, than putting screens, but is it an effective way to prevent the midges from coming into people's homes? We do not want to, in the end, create new problems – people having different kind of pests because of the kind of trees that we plant near their homes or around the reservoirs.

Sir, I noticed that Lower Seletar Reservoir was not mentioned by Minister among the water bodies that have the problem of midges. My residents have been bringing up this issue on midges and mayflies. So, I would like to ask the Minister, will PUB carry out preventive measures for Lower Seletar Reservoir before it becomes, like my Parliamentary colleague mentioned, a "horror movie scene". So, I hope something can be done for the Lower Seletar Reservoir area.

We do monitor for every reservoir and we take the appropriate measures. We do not want a sledgehammer for a small problem or small hammer for a big problem. So, appropriate measures.

I thank the Minister for the clarification. Just one clarification. Part of the problem is climate change and something we cannot alter. I was wondering whether we have looked at ways of changing the micro climate around the reservoirs. Because this only happens in certain reservoirs and I agree that it is because of the water, but there have been some studies that looked at the vegetation and the micro climate around the banks of the reservoirs. Can we look at that?

I think we will study all these. Thank you.

We will study how we can help residents. We must also take this into consideration for the kinds of things we have to spend, for when we try to tackle bigger issues in years to come, when climate change is upon us. We have not really understood properly how it will affect Singapore. What the Prime Minister has mentioned are only those things that we know can happen and should start working on from now. Issues around pests, are in fact more dangerous and I will mention it in my next Parliamentary Question (PQ) reply, around mosquitoes. They present a more imminent danger than perhaps what midges will present to us, and not to just particular areas around the reservoirs, but in fact, to the whole of Singapore.

So, in consideration of all those issues, yes, we will study them. We will see what we can do for localities but we also should know that our resources are limited; we have to put focus on important areas and not over promise on other areas, but rather, to over deliver.