Since January 2019 we have been investigating the causes of poor water quality at Terrigal Beach, the Haven and the coastal lagoons. We have released the most recent report into the findings and the actions we have already taken to improve water quality.
We know as a result of the early audit investigations that sewage is entering our systems in some locations. To discover where this is happening, more than 115.4kms of sewer mains and 1036 private properties have been inspected. We have discovered 41kms of sewer mains needing repair, 95% has been repaired to date, and discovered 23 illegal connections as well as various other private defects. We are working with these residents to ensure they can be rectified.
To find out more about this project and assist in the identification of potential sources of pollution you can:
- view the Frequently Asked Questions
- see what works have already been identified or completed as part of this process
- view the key documents associated with the Audit including summary reports, data information and report concepts
Together, Council and DPIE have been working on a number of reports to provide the community with more information on water quality issues in the Terrigal region.
Results of the audit are summarised in Towards Safer Swimming: Terrigal Beach and Haven.
There are also nine technical reports that describe the results of the Terrigal Water Quality Audit research:
- Towards safer swimming – Terrigal Region: Stormwater catchment audit
- Microbial source-tracking to assess the spatial extent and temporal persistence of water quality issues at Terrigal Beach
- Sewer network remediation and works program for Terrigal and the coastal lagoon catchments
- Towards Safer swimming – Terrigal region: Terrigal Bay: Sediment contamination
- Towards safer swimming – Terrigal region: Turbidity in Terrigal Bay
- Towards safer swimming – Terrigal Region: Calibration and Verification of a 2D Hydrodynamic Model for Terrigal Bay
- Microbial source-tracking in NSW coastal habitats
- Towards Safer swimming – Terrigal region: Outcomes of the community engagement program for Terrigal and the Coastal Lagoons
- Microbial source-tracking to assess water quality in Central Coast Lagoons (UTS technical report) – in preparation
About the audit
The Terrigal and Coastal Lagoons Audit is a comprehensive water quality improvement program being undertaken in partnership between Central Coast Council and the NSW Government’s Department of Planning, Industry and Environment (the Department).
The Audit is investigating water quality at Terrigal Beach, Terrigal Haven, Terrigal Lagoon, Wamberal Lagoon, Avoca Lagoon and Cockrone Lagoon. A team of scientists from the Department and from Council are working collaboratively with technical experts and operational staff to assess possible sources of pollution in each catchment, determine the impact on long-term water quality, and prioritise remediation works.
How can you help?
The health of our waterways is dependent on the health of the broader catchment areas – whatever comes down the rivers or enters the stormwater, ends up in our waterways and can have good or bad impacts. Our personal actions can directly affect the health of our waterways, not only right where we live or work but all the way to the estuaries and ocean. By working together, we can all do our bit to improve and protect our beautiful coastal areas now, and for the future. We have developed the Waterways fact sheet to inform the community on how they can assist in the ongoing health of our waterways:
Council will continue to share the progress of the audit program through information shared on this page and on the interactive map.
** Comments that were dropped on the interactive map or submitted via on the online form will not be made publicly visible. This is to avoid publicly identifying private properties. However please note under the Government Information (Public Access) Act 2009 (GIPA Act), members of the public have a right to access certain information held by Council except in instances where there is an overriding public interest against disclosure.**
Is it safe to swim at Terrigal Beach, Haven, and Lagoon?
It is safe to swim at Terrigal beach, Haven and the coastal lagoons if you follow the rainfall recommendations on our advisory signs.
In general, this means:
“This area can be affected by stormwater pollution for up to three days following heavy rain. Swimming during this period is not recommended.”
Water quality audit samples from Terrigal Beach, Haven and Lagoon in dry weather indicate that:
- Terrigal Beach as a whole is rated as ‘Good’ to swim in 96% of the time (100% of the time at the Surf Life Saving Club)
- Terrigal Haven is ‘Good’ to swim in 89% of the time
- Terrigal Lagoon is ‘Good’ to swim in about 70% of the time
When swimming at one of the Central Coast's beautiful beaches, please always follow the lifeguards' directions and obey warning signs. For patrolled beaches the safest spot to swim is between the flags.
Is the rockpool at Terrigal Beach safe to swim in?
Water samples collected at the rockpool from January to September 2020 show that the rockpool is safe to swim in 100% of the time during dry weather. This indicates that swim-safety in the rockpool is not at risk due to the proximity of the stormwater pipes when there has been no rain for three days. Council is continuing to monitor water quality for the rockpool area.
How does Council keep the community informed about water quality and swim-safety?
Permanent swimming advisory signs are located at swimming sites that may experience poor water quality following rainfall. These signs read:
“This area can be affected by stormwater pollution for up to three days following heavy rain. Swimming during this period is not recommended.”
Council also updates our Beachwatch Program website with the latest sampling results and any risk warning notices as necessary.
To see daily predictions for water quality at Central Coast beaches visit the NSW Beachwatch website.
Why has Terrigal’s water quality improved?
In the 2019-2020 State of the Beaches Report, Terrigal has retained a “Good” rating for the second consecutive year, an improvement on the “Poor” rating in the preceding three years.
Current indications are that relatively dry weather during the 2018-19 and 2019-20 summer swim seasons compared to the preceding three years may have been the primary influential factor for the change in category.
Since January 2019 Council has increased the frequency and spatial resolution of sampling surrounding routine Beachwatch Program swim sites at Terrigal Beach, Rockpool and Lagoon, to determine the nature of microbial water quality risks to primary contact recreation users.
Further studies undertaken as part of the audit identified a major source of the contamination found in stormwater outlets during rainfall was from sewage infiltration due to defects in public and private infrastructure assets. A program for upgrading the sewer and stormwater infrastructure was developed and is being implemented. The sewer and stormwater system upgrades are likely to be contributing to the improvement of water quality at Terrigal Beach. Keep up to date on progress with upgrades on our interactive catchment audit map.
In addition to rainfall, other environmental factors influence changes in recreational water quality gradings at beach swim sites. These include the wave conditions and whether the nearby lagoons are open or closed to the ocean.
What is a water catchment audit?
A water catchment is an area where water is collected by the natural landscape. Rainwater run-off flows downhill by gravity. Flow pathways can include the stormwater network, creeks or groundwaters. In our coastal catchments, most of the stormwater volume will eventually reach our coastal ocean swim sites via transit through the lake and lagoon systems or direct outflow pathways.
A catchment audit can use catchment health indicators to assess:
- The types and sources of pollution within a catchment
- The types and condition of biodiversity and habitats
- The amount of water available for municipal or agricultural use, and
- The water quality (including microbiological analyses for swim safety risk assessments)
Where are audits being done?
Currently, audits are being undertaken in the Terrigal Beach, Haven and Lagoon, Avoca Lagoon, Wamberal Lagoon, Cockrone Lagoon, Cabbage Tree Bay, Toowoon Bay Beach and Canton Beach catchments.
What is causing elevated microbial levels at Terrigal and the coastal lagoons?
Issues at Terrigal and the coastal lagoons with respect to swim safety are largely a result of elevated microbial levels.
A microbe is an organism which is microscopic, which means it’s too small to be seen by the unaided human eye. Microbes that present risks to swimmers include some bacteria, viruses and protozoa.
Microbial contamination is the presence of specific microbes in unnatural locations or higher than natural background levels. Rather than measuring specific harmful organisms (pathogens), easily measurable microbes that may co-exist with harmful ones are used to indicate the potential presence of higher-risk organisms such as viruses, that are not readily measurable by most analytical laboratories.
When referring to water quality for swim safety, microbes that are indicators for the presence of human- or animal-derived pathogens are used. For example, Enterococci, a microbe that grows in the gut of warm-blooded animals, indicates faecal contamination. Whilst microbial contamination could come from humans (sewage) which could hold harmful pathogens, it could also come from birds, dogs, cats, rabbits, pigs or livestock that may be farmed in a local catchment area and generally pose a lower risk to swimming safety.
To study microbial contamination types and sources audits typically start sampling in the downstream waterways (eg, coastal lagoon and ocean sites) and drain outlets to better understand the composition and loadings of pollution, as well as the main outflow source points contributing to adverse changes in water quality. The audit then moves up into the catchment, for example, the developed (or built) environment, and assesses the dynamics of pollution in the stormwater to identify locations of high or low priority for remediation.
Investigations so far indicate that aging sewer and stormwater infrastructure, defective connections, and wildlife are major sources of microbial contamination in Terrigal Beach and the coastal lagoons.
What are the solutions to microbial contamination of waterways?
The primary solution to poor recreational water quality is a systematic inspection of the sewer network and repair including pipe relining and rectification of defective infrastructure and illegal connections.
Major investigations into the condition of these assets have and continue to be undertaken.
Stormwater diversion or treatment for microbial contamination is not considered an ideal solution to water quality issues, because the best solution to pollution is prevention. Council and the NSW Government have been undertaking investigations to detect issues in the catchment, and Council are undertaking a number of infrastructure improvements in the catchment to improve water quality.
Water quality information obtained during the Terrigal and Coastal Lagoons Audit informs direct investigations for remediation, such as pipe-based camera surveys (CCTV), dye testing, and smoke testing to further pinpoint and in turn remediate the main causes of pollution.
Have investigations only assessed microbial contamination (sewage)?
Central Coast Council and the NSW Government have collected data for a number of water quality parameters in Terrigal and the coastal lagoons. These include but are not limited to:
Water samples: Nutrients, Dissolved Oxygen, Temperature, Salinity, pH, Fluorometry, CDOM (Coloured dissolved organic matter), Turbidity (dirt in the water), Algal counts (where indicated by high Chlorophyll levels), Chlorophyll-a, Enterococci counts, Genomics.
Sediment (sand/mud) samples: Nutrients, TOC (total organic carbon), Enterococci counts, microplastics, pesticides, herbicides and metals.
Litter and sediment: Through the wet weather sampling program, litter, sediment and turbidity are being assessed to inform future works at Terrigal and the coastal lagoons.
What works have been, and continues to be, undertaken by Central Coast Council to assess and improve water quality at Terrigal and the coastal lagoons?
In January 2019, Council commenced an initial catchment audit at Terrigal Beach, Haven and Lagoon coastal sites. In partnership with the NSW Government, the scope of the audit was significantly expanded. View the full report on the first phase of the audit.
Key components of the expanded audit include:
- Water quality monitoring programs for Wamberal, Avoca and Cockrone lagoon catchments, as well as nearby control sites
- Applied innovative DNA-based techniques to identify whether sources of faecal contamination in the catchment and beach and lagoon receiving waters come from human or animal sources (e.g. dogs, birds)
- Assessed the extent of microbial contamination in the off-shore zone of Terrigal Beach where swimmers cross to Terrigal Haven
- Developed a hydrodynamic-wave coupled model to understand the circulation patterns and residence times of pollutants in the Terrigal Bay embayment
In addition to the water quality audit Central Coast Council has a sewer network remediation program that is aimed at eliminating the sources of microbial contamination within the catchment. Through CCTV, smoke testing, dye testing and water sampling of the stormwater and sewer networks, Council is further able to identify sources of possible microbial contamination of stormwater (eg, defective or misconnected sewer infrastructure) initially identified as broader areas of interest from the downstream water quality results.
What information is available to the community?
The findings of the audit are available to the community via the document library of this website.
This website provides periodically updated technical reports, and an interactive map showing broken and fixed pipes as well as information about catchment-based smoke testing and other investigations.
Where Council infrastructure is identified as a source of pollution, these locations are immediately scheduled for infrastructure refurbishment, with outcomes officially reported and made public.
How has Council found where the microbial contamination is coming from?
Council have used several methods to investigate where the microbial contamination is coming from. They include those listed below, ensuring that the method is appropriate to assess a specific problem.
Smoke testing for illegal connections: pumping artificial smoke into the sewer network. Smoke testing is used when sewer pump station data indicates rainwater or groundwater is infiltrating from the catchment into the sewer network, which can cause manhole overflows in wet weather. Smoke testing tells Council if houses or businesses have their stormwater (gutters and drainage) connected illegally to the sewer network.
Dye testing: placing non-toxic dye into the sewer network where a break is suspected. If the sewer network is in-tact, the dye travels to the local treatment plant via the sewer network. If there is a break in the sewer pipes, dye may leave the sewer network and leach into the stormwater network. Staff monitor stormwater after dye is placed in the sewer network to detect if dye is visible in the stormwater, which indicates transfer of sewage into the stormwater network.
CCTV camera inspection of sewer network: a camera is mounted on a wheeled buggy that is inserted in to the sewer pipe via a manhole. The CCTV camera records video and photos of the pipe condition, to assess defects in the sewer pipe. Defects may include cracks, breaks, displaced joints, third party damage, debris, groundwater infiltration and obstructions. The locations of the defects are located and recorded for further remedial maintenance work.
CCTV camera inspection of stormwater network: a camera is mounted on a wheeled buggy that is inserted to the stormwater pipe or culvert via a drainage pit or access chamber. The CCTV camera records video and photos of the pipe (or culvert) condition, to assess defects in the stormwater pipe. Defects may include cracks, breaks, displaced joints, third party damage, debris, groundwater infiltration and obstructions. The inspection work is performed in dry weather only.
Water samples: sampling stormwater in wet weather helps to direct CCTV and dye testing to detect sewage input. Bacteria testing can be paired with other complementary tests such as ammonia and trace pharmaceuticals (e.g. testing for painkillers, anti-inflammatory medications and caffeine).
What is an illegal connection?
There are two types of illegal connections being investigated in the audit:
Stormwater to sewer connections: If a house roof (or other rain collecting drainage system) is connected to the sewer network, the rainwater flows directly to sewer rather than to the stormwater network. The sewer network is not designed to hold this increased volume of water, so the system may overflow, usually at designated overflow points depending on the number of illegal connections, rainfall intensity and duration. This allows sewage to enter the environment untreated.
Sewer to stormwater connections: Where the household sewer is connected to stormwater, wastewater flows directly to stormwater and then into creeks, estuaries, lagoons and the ocean.
Why isn’t the water completely clean and healthy at our beaches, waterways, lakes and lagoons?
Any beach, waterway, lake or lagoon in a developed or developing area will have less than completely clean and healthy water. The main impacts on water quality in developed or developing areas are:
Stormwater runoff: all the water which runs off our streets, parks, gardens, roofs, gutters, roads and other hard stand areas when it rains ends up, for the most part, at our beaches, waterways, lakes and lagoons. Along the way that stormwater could mix with dirt, oil, grease, litter, chemicals, animal waste, sewer waste from cracked or damaged sewer pipes and illegal connections, grass, leaves, on-site septic system overflows and much more.
Everyone can help stop pollution from entering our waterways. Find out how you and your family can help Council and local Landcare groups facilitate cleaner waterways.
Sewer overflows or leaks: globally, sewer systems overflow in periods of heavy rain due to rain infiltration into the sewer pipes. Rainwater gets into the sewer system through cracked, damaged or displaced pipes as well as private properties illegally connecting their stormwater system to the sewer. The extra water in the sewer network causes sewage overflows.
Poor water quality in urban areas is not a new phenomenon, and waste materials affecting waterways and the ocean is a common issue in both developed and developing countries. Monitoring programs, like NSW Beachwatch and Waterwatch, are undertaken to identify locations that experience water quality declines and to prompt audit investigations and improvement programs.
What are the primary causes of blockage in our sewer system?
Tree root ingress and the flushing of inappropriate items are the main causes of partial and total blockages in our sewer system.
The beach smells like sewage, is it sewage?
Previous water quality sample results have shown that the smell is from decaying seaweed.
The occasional smell, discoloured appearance or presence of foreign material in water flowing to Terrigal has been reported to Council or the EPA by members of the public. In each case, investigations have shown that the anomaly is due to decaying seaweed in the water, on the beach or in the stormwater pipes. This decaying seaweed can produce hydrogen sulphide known as “rotten egg gas” and is a natural marine process.
It is noted that there is a network of sewage pumping stations and manholes located throughout the Terrigal catchments, with the sewage pumping station located at Pine Tree Lane and manhole on Kurrawyba Avenue known to contribute to odour. If odours are observed at Terrigal, the community are encouraged to contact Council directly, so Council can investigate the source of these odours at the time they occur.
When water or sewer network issues occur, or are suspected, our primary concern is the health and safety of the public and the environment. We have crews on standby 24 hours a day, 365 days a year so please call Council immediately – day or night – on 1300 463 954 if you experience water or sewerage concerns.
Is the dirty water I’ve seen in the lagoon, ocean or stormwater pipes sewage?
Sewage is comprised of 98% water, so dirty or pungent water in the lagoon, ocean or stormwater pipes does not necessarily indicate raw or treated sewage. There are many possible reasons water may look and smell bad, including natural process.
Rotting vegetation, seaweed and algal blooms can smell bad and lead to discoloured water, including brown, yellow, red, pink, white or grey/green water. Rotting seaweed, algal blooms or other natural bacterial populations may also look like dirty water or a foam or oil slick on the surface.
Council does not recommend swimming in or near an algal bloom as some species, such as blue-green algae (cyanobacteria), can produce toxins that are harmful to human and animal health.
Activities in the catchment can also impact on water quality and odour. These could include, washing cars in the gutter where all the soap suds run down the drain, over fertilising gardens, soil loss from building and development sites, gardens, parks and roadways, animal waste and even grass and leaves which wash off our streets and down the drains.
Some of the materials in this runoff can provide ideal conditions for natural bacteria to grow and the decomposition of many of these materials may cause a smell, impact on the colour of the water, or, depending on the various sources of the catchment runoff, increases risks to swim safety.
For information on other possible pollutants, please see FAQ: “Is there any evidence of herbicide, pesticide, metal or microplastic contamination in Terrigal bay and Haven?”
Is there any evidence of herbicide, pesticide, metal or microplastic contamination in Terrigal bay and Haven?
Central Coast Council and the NSW Government have collected samples throughout Terrigal bay and the Haven to assess if the sediments had elevated levels of oil and grease, herbicides, pesticides, metals and microplastics compared to control sites at Wamberal North Avoca and Avoca beaches.
The study found that sediments in Terrigal bay, the Haven and the control beaches had no herbicide, pesticide or microplastics. Oil and grease residues in the sediments were also undetectable with exception of one site in the Haven where oil and grease residues were slightly above the methodological detection limit. For more information on contaminants in Terrigal, please see report Towards safer swimming – Terrigal region: Terrigal Bay sediment contaminants report.
Why is Terrigal’s beach water sometimes cloudy?
Turbidity can be perceived as cloudiness in the water and a lack of ability to see through the water. Turbidity is affected by presence of biotic (phytoplankton) and abiotic (sediment) factors. Together with the NSW Government, Council has sampled the sediment across Terrigal Beach and the Haven to investigate reports of high turbidity.
The re-suspension of fine sand on the seafloor plus occasional wet weather inputs from Terrigal Lagoon and 7-drains can increase the amount of sediment in the ocean, contributing to turbidity in the bay. Regionally-wide algal blooms in the spring-summer can contribute to the turbidity, particularly in the Haven. Aside from urban stormwater runoff, the majority of these sources are part of normal processes. For more information on turbidity in
Terrigal, please see report Towards safer swimming – Terrigal region: Understanding turbidity and discolouration in Terrigal Bay.
Why does water flow from the stormwater pipes in Terrigal during dry weather?
Staff have assessed the water flowing from the stormwater pipes at the southern end of Terrigal beach during dry weather and determined that the water comes from a range of sources such as natural groundwater, pumped groundwater, tidal infiltration and activities in the catchment. The dry weather flow can be subject to different flow rates during the day. Water in the stormwater pipes in dry weather comes from water usage in the catchment such as watering lawns, fire sprinkler testings and automated groundwater pumping such as occurs in underground carparks.
Groundwater: Underground springs and ground water naturally travel and exchange with the ocean and can infiltrate into stormwater pipes resulting in dry weather stormwater flows.
Pumped groundwater: Since groundwater naturally flows from high points in terrain to the ocean over long durations, manmade structures (buildings/carparks) can interrupt or intercept this flow, creating a nuisance in buildings. Sump pumping is a common method used to remove the groundwater from the basement or foundations of the structure and expedite the removal of water to protect residents and businesses from dampness and flooding in carparks and buildings.
Tidal Infiltration: Due to the flat terrain and low elevation of Terrigal CBD, spring high tides can push water back into stormwater pipes and where wave action stacks sand up within pipes, these sand berms can give way suddenly and release sudden flows of water. This is a very common process in the main Terrigal stormwater outflow where tidal infiltration at least as far as Pine Tree Lane is common on high tides.
Catchment activities: Catchment activities are things that the community do that use tap water. In streets and gardens, runoff can be caused by e.g. car washing, hosing paths, watering lawns and gardens. Additionally, fire service sprinkler testing often undertaken in large buildings on a monthly basis inputs water into the stormwater network in dry weather.
Sometimes, the water can exit the stormwater network in a rush. Waves can push sand into the stormwater pipes causing temporary blockages. When water from the catchment flows in dry weather (from groundwater pumps, sprinkler tests and catchment activities) it may be trapped behind the sand. The water builds up behind the sand creating pressure. When the pressure behind the sand becomes too great, the water breaks through the sand barrier resulting in a sudden outflow of water.
How is Council ensuring that water quality at Terrigal Beach remains ‘Good’?
As infrastructure works continue to be completed in the catchment, we expect to see improvements in the water quality however this may still take some time. Due to a wide range of factors including natural variability, the presence of natural sources of bacteria which may affect water quality and the length of time required to collect enough samples, it is difficult to predict. In general, water quality advisories related to swim safety are based on about 100 samples collected over three consecutive years. Accordingly, it may take up to three years post remediation works for an interpretable microbial water quality trend to become apparent in the data sets.
To allow Council to measure water quality improvements in the interim, we sample regularly at key outflow locations of pipes that discharge directly to the beaches and lagoons. The results from this sampling program will more clearly and quickly assess if water quality from the pipes has improved in response to remediation works and improved catchment management. Council has reports available which highlight the water quality results. Please refer to Terrigal Catchment Audit - Report 2 for the most recent water quality data.
How long will the audit take to complete?
The program has a series of anticipated timeframes for each location (Table below). Investigation and works programs are expected to extend to June 2025 to complete for all the audit catchments, including follow-up monitoring periods. The Terrigal and coastal lagoons audits have seen considerable progress, particularly in the Terrigal Beach, Haven and Lagoon catchments, with Phase 1 completed, and Phases 2 and 3 well underway. Once priority remediation works have been completed in these areas, the works program will move to target priority zones in the Avoca Lagoon catchment; and will bring into focus investigations within the remaining lagoon catchments of the audit (i.e. Wamberal and Cockrone Lagoons).
How can you help us prevent, detect or fix problems in the infrastructure?
There are lots of things members of the community can do to help improve local water quality.
Do you suspect a sewer block, overflow, broken sewer manhole or smell something like sewage? When alleged blockages and overflows are reported, our primary concern is the health and safety of the public and the environment. We have crews on standby 24 hours a day, 365 days a year so please call Council immediately – day or night – on 1300 463 954 if you experience water or sewerage concerns.
Only ever flush the three Ps down your porcelain throne – Poo, Pee and Paper – everything else needs to go into the appropriate bin.
Think twice before flushing things down drains or toilets (and simply don’t do!) - household waste such as food scraps, fats and oils, cigarette butts, nappies, dental floss, sanitary items, cotton buds, stickers on fruit, and wipes – even if they are labelled 'flushable' all belong in the bin, not the sewer. These not readily homogenised items (non-miscible), particularly fats and oils, cannot be easily mixed into the liquid waste stream and increase the likelihood of sewer network blockages, leading to more frequent manhole overflows and damage to pipes.
Renovating or digging? Make sure you 'Dial before you Dig' – this is a free national service which locates underground pipes to prevent damage during digging. If renovating, make sure you do not damage underground sewer pipes. Cracks and breaks can cause sewage to leak into the groundwater and stormwater, contaminating our waterways and coastline.
Love your garden? Make sure garden beds and trees are located away from the sewer pipes. Tree roots can cause damage that is hard to detect from the surface and can be costly to repair or replace.
Is your sewer and stormwater correctly plumbed or working correctly?
- Does your overflow relief gully go underwater when it rains? Raising your overflow relief gully can help us to improve the sewer networks performance by preventing rainwater in the sewer network.
- If you own an on-site sewer system, be sure to have it inspected on a regular basis.
- Have your sewer system checked and make sure it connects to the sewer network and not the stormwater network.
- Have your stormwater assets (pipes that convey rainwater from the house, shed, garage or rainwater tank overflow) checked and make sure they connect to the stormwater network. Connecting your stormwater to the sewer network overloads the sewer's capacity and can cause overflows in rainy weather.
What should you do if you suspect a sewerage block or overflow in your area?
When blockages and overflows are reported, our primary concern is the health and safety of the public and the environment. We have crews on standby 24 hours a day, 365 days a year so please call Council immediately – day or night – on 1300 463 954 if you experience water or sewerage concerns.