Water Quality Monitoring in the Upper Ourimbah Creek Catchment

The EPA and the Department of Climate Change, Energy, the Environment and Water (DCCEEW) have conducted sampling of the upper reaches of Ourimbah Creek and its tributaries since 2016. We have monitored for ammonia which is an indicator of leachate from landfills.

Water sampling conducted in 2024 did not show any adverse impacts to water quality in the catchment from landfill operations.

In January 2025 the Central Coast Council advised they had detected PFAS in raw, untreated water in the upper reaches of the Ourimbah catchment. The Council is working with NSW Health, DCCEEW and EPA.

Read the sampling results at Central Coast Council Drinking Water Quality.

The most recent DCCEEW sampling occurred in February 2025 and included testing for PFAS. An additional monitoring location on Ourimbah Creek upstream of the confluence with Hallards Creek and Stringybark Creek was also included.

Summary of results

Water quality parameters were generally good with the exception of elevated total nitrogen in Stringybark Creek and Ourimbah Creek and total phosphorus in Hallards Creek and the northern arm of Stringybark Creek. Oxidised nitrogen was elevated at all sites, as were aluminium concentrations at all sampling locations except Ourimbah Creek. No semi-volatile organic compounds were detected in any of the water samples. These results are consistent with previous reports.

The aluminium concentrations are likely indicative of background concentrations in creeks of the area rather than pollution. Given the elevated oxidised nitrogen concentrations across all sites, there are likely multiple sources of runoff influencing the nitrogen load in the Ourimbah Creek catchment.

PFAS compounds were detected at all sites except Hallards Creek.

PFAS concentrations are below the recreational and drinking water guideline values but exceed the ecological water quality guideline values for the protection of 99% of freshwater species at the sites it was detected. The 99% species protection level is recommended for slightly to moderately disturbed ecosystems, particularly for chemicals that bioaccumulate and biomagnify in wildlife such as PFOS and PFOA.

Sample results

Physico-chemical properties, metal and nutrient concentrations of the water samples collected from Ourimbah Creek, Hallards Creek and Stringybark Creek on 13 February 2025.

^a Health-based guideline values (NHMRC 2024).
^b For physio-chemical properties and nutrients, the ANZECC/ARMCANZ (2000) default trigger values for lowland rivers in south-east Australia have been applied as screening criteria unless otherwise specified. For metals, the ANZG (2018) default guideline values (DVGs) for 95% species protection have been applied as screening criteria unless otherwise specified.
^c The units for the default trigger value for turbidity are NTU. This range can be directly compared to results reported in FNU despite the unit difference.
^d Dissolved metal (<0.45 µm filtered) levels reported unless otherwise stated.
^e To account for the bioaccumulating nature of selenium, it is recommended that the 99% species protection level default guideline value is used for moderately disturbed systems.
^f Default trigger value for NSW and Vic east flowing coastal rivers (ANZECC/ARMCANZ 2000).
	Water Quality Default Guideline Value^b	Hallards Creek	Ourimbah Creek	Stringybark Creek (SB1)	Stringybark Creek - North (SB2)	Stringybark Creek - South (SB3)
	Water Quality Default Guideline Value^b	13 Feb	13 Feb	13 Feb	13 Feb	13 Feb
Temperature °C	-	20.6	20.9	20.2	20.3	19.9
pH	6.5-8.0	7	7.2	7	7	6.9
Conductivity (µS/cm)	125-2200	110	130	160	190	150
Turbidity (NTU)	6‐50^c	1.8	13	6.4	2.2	3.6
Dissolved oxygen (% Sat)	85-110	94.1	94.5	94.1	89.9	93.9
Alkalinity (mg/L CaCO3)	-	8	11	15	20	12
Metals^d(μg/L)
Aluminium	55	60	<40	90	70	110
Arsenic	13	<0.5	<0.5	<0.5	<0.5	<0.5
Boron	940	<100	<100	<100	<100	<100
Cadmium	0.2	<0.05	<0.05	<0.05	<0.05	<0.05
Chromium	1	<0.5	<0.5	<0.5	<0.5	<0.5
Copper	1.4	0.4	0.4	0.6	0.5	0.7
Lead	3.4	<0.1	0.1	<0.1	<0.1	0.1
Manganese	1900	7	6	5	5	5
Nickel	11	<0.5	<0.5	0.7	0.8	0.6
Selenium	5^e	<2	<2	<2	<2	<2
Silver	0.05	<0.05	<0.05	<0.05	<0.05	<0.05
Zinc	8	2	1	1	<1	2
Nutrients (μg/L)
Ammonia as Ammonia Nitrogen	20	<10	<10	<10	<10	<10
Oxidised nitrogen NOx‐N	40	130	710	140	190	130
Reactive Phosphorus as P	20	<10	<10	<10	<10	<10
Total Phosphorus as P	25^f	70	<10	20	30	<10
Total Nitrogen as N	350^f	300	1000	400	1000	600

PFAS concentrations of the water samples collected from Ourimbah Creek, Hallards Creek and Stringybark Creek on 13 February 2025.

^a Health-based guideline values (NHMRC 2024)
^b Freshwater ecological guideline for 99% species protection (PFAS NEMP 2025)
	Australian Drinking Water Guideline^a	Water Quality Default Guideline Value^b	Hallards Creek	Ourimbah Creek	Stringybark Creek (SB1)	Stringybark Creek - North (SB2)	Stringybark Creek - South (SB3)
	Australian Drinking Water Guideline^a	Water Quality Default Guideline Value^b	13 Feb	13 Feb	13 Feb	13 Feb	13 Feb
PFOS (µg/L)	‐	0.00023	<0.0003	0.0004	0.0052	0.0093	0.0009
PFOA (µg/L)	0.56	19	<0.0005	<0.0005	0.0078	0.0128	<0.0005
Sum of PFHxS and PFOS (µg/L)	0.07	-	<0.0003	0.0004	0.0189	0.0469	0.0015

NSW Health recommends that untreated water from rivers and creeks should not be used for drinking or cooking without appropriate treatment. Untreated water may contain disease- causing micro-organisms, chemical contaminants or algal blooms.

For more information visit Drinking surface water - Water quality (nsw.gov.au) or read our Water quality monitoring - Ourimbah Catchment fact sheet (PDF 935KB).

PFAS in the Central Coast region

Has PFAS been found in the Central Coast community’s drinking water supply?

No. Central Coast Council detected low levels of PFAS during routine catchment monitoring in raw, untreated water in Ourimbah Creek. It has not detected PFAS in drinking water supplies from any dams currently providing drinking water.

PFAS was not detected in drinking water supplies from any dams currently providing drinking water.

You can find Central Coast Council’s water sampling results here: Drinking water quality | Central Coast Council.

Is there a risk to the community?

The presence of PFAS in the environment does not necessarily mean there is a health risk.

While there have been detections of PFAS in the Ourimbah Creek catchment, they have been found in a raw water source, not in the Central Coast’s drinking water supply. Additionally, the locations where PFAS have been found are largely inaccessible to the public so any potential risk to human health is considered very low.

NSW Health also advises that water from rivers and creeks should not be used for drinking or cooking without appropriate treatment. Untreated water may contain disease causing micro-organisms, chemical contaminants or algal blooms. For more information visit Drinking surface water – Water quality (nsw.gov.au).

Has the source of the PFAS been identified?

Central Coast Council is responsible for the management of the water catchment and drinking water supply for the Central Coast and the EPA has encouraged them to investigate all potential PFAS contamination sources in the catchment. We are meeting regularly with the Council to stay up to date on their investigations.

The EPA has also undertaken sampling in the waterways very close to the Mangrove Mountain landfill to determine if they are a potential source of PFAS contamination. We are progressing a range of measures to improve the environmental management of this facility.

Read about our regulation of the Mangrove Mountain landfill.

Has the EPA found PFAS in its testing of waterways near the Mangrove Mountain landfill?

The EPA and DCCEEW conducted sampling in January and February this year and results did show the presence of PFAS at four locations in Stringy Bark Creek near the landfill. Results were below the current NHMRC Recreational Water Quality Guidelines but above the Ecological Guidelines.

These waterways are not easily accessible to the public and are not known recreational swimming or fishing spots, so these results suggest a low risk to the community of PFAS exposure in these locations.

Results of the sampling are on this webpage.

Are people using groundwater (bore water) at risk?

Central Coast Council is currently working with the EPA, DCCEEW and NSW Health to identify groundwater users in the area as part of their investigation and risk assessment. To date we have no evidence that groundwater users in the area may be at risk of PFAS exposure but are progressing additional investigations at Mangrove Mountain landfill to understand what, if any, PFAS contamination may be occurring on or off site.

Have there been PFAS detections in other Central Coast waterways?

The EPA is leading an investigation program to assess the legacy of PFAS use across NSW, focusing on sites where it is likely large quantities of PFAS may have been used in the past.

The former Munmorah Power Station was identified as being significantly contaminated and PFAS was detected in waters adjacent to the site. In response, seafood caught in the Tuggerah Lakes system was tested to determine if precautionary dietary advice was required. Results confirmed that the community can continue to eat seafood caught in the Tuggerah Lakes as part of a balanced diet.

More information about PFAS

Updated 29 May 2025