NSW Environmental Protection Agency NSW Government
 

Assessing the health of Lake Macquarie results

Over 3 years, water and sediment samples were collected across multiple locations around the southern side of Lake Macquarie.

The study investigated the following key lines of evidence:

  • surface water quality – chemical assessment
  • surface sediment quality – chemical assessment
  • surface sediment quality – toxicity assessment
  • surface sediment quality – newly deposited sediment assessment
  • benthic community composition (including eDNA) – Lake Macquarie

The Lake Macquarie synthesis report consolidates all the individual lines of scientific inquiry into a weight of evidence framework to provide an overall assessment of the southern lake’s health.

Overall, the data reveals the lake is in relatively good condition. The results show that despite a long history of industrial and urban activity, the lake’s health has improved with metal concentrations dropping since sampling in 2011.

All raw data from the project is available on the NSW SEED (Sharing and Enabling Environmental Data) portal.

Surface water quality chemical assessment

  • Few samples or sites were found to have metal concentrations that exceeded the Australian and New Zealand Guidelines for Fresh and Marine Water Quality (ANZG 2018). In some samples at a few sites away from the power stations, aluminium, copper, zinc and manganese were found at levels above these guideline values. The synthesis report found that this is most likely from catchment inflows.
  • Temperature was elevated in waters close to both power stations discharge channels, by between 5-10 degrees above background temperatures around the rest of the lake.
  • Total nitrogen and phosphorous are below guideline values, while in the areas where key tributaries flow into the lake, more bioavailable nutrients (oxidised nitrogen, ammonia and dissolved phosphorous) were above the guideline values.
  • Power station ash dams act as a potential reservoir for some metals and nutrients although discharges are infrequent as water is isolated, captured, reused and recirculated. There was no evidence of adverse impacts on Lake Macquarie’s water quality from metals and nutrients in the coal ash water that is collected and returned to the coal ash dams.

Read the full report Lake Macquarie surface water quality – chemical assessment (PDF 13.6MB)

Surface sediment sampling and newly deposited sediment assessment

  • No sites within the southern section of Lake Macquarie (the section of the lake near the power stations) exceeded the screening criteria based on their bioavailable metal concentrations. Two of the sites located within the northern section of the lake exceeded the Sediment Quality Guideline Value for lead (ANZG, 2018) based on dilute acid-extractable metal concentrations.
  • Comparison with a study published in 2011, indicates that in general there is a decline in concentrations of metals, especially closer to the power stations.
  • Total metals are above the background level that would be expected if the lake was pristine but are generally below guidelines values that would impact marine life.
  • Comparisons of the surface sediment data (top 5 cm, collected in 2022) and newly depositing sediment data (collected in sediment deposition traps in 2024) found that concentrations of copper, lead and zinc were lower in the sediment that was collected from sediment traps than sediments already on the lake floor. Arsenic and mercury concentrations were found at similar concentrations in the sediment traps and the lake floor sediments in some areas.
  • With no new significant inputs of metals, it can be expected that lake sediments will continue to improve over time as metals are bound in buried sediments or move out of the system.

Read the full report Lake Macquarie surface sediment quality – chemical assessment (PDF 14MB)

Read the full report Lake Macquarie surface sediment quality – newly deposited sediment assessment (PDF 3.8MB)

Surface sediment toxicity assessments

  • No acute toxicity (levels causing mortality) was observed at any of the 10 test sites.
  • No toxic chronic sub-lethal effects (levels causing reproduction problems) were observed in the southern section of the lake, including near the power stations.
  • Low-level chronic toxicity was observed in two sites in the northwest section of the southern lake.

Read the full report Lake Macquarie surface sediment quality toxicity assessment (PDF 2.3MB)

Benthic community composition (including eDNA)

  • There was significant temporal and spatial variability in the indicator species assessed across the lake. These results indicate normal variation in the absence or presence of species that are largely driven by natural spatial variability across the lake.
  • Patterns in the presence or absence of tolerant and sensitive species was assessed using well-established biological metrics that consider species richness, abundance, sensitivity and community structure for certain groups of macrofauna and eukaryotes. This work showed no clear association between metal concentrations causing variation in community composition.

Read the full report Benthic community composition for Lake Macquarie (PDF 5.2MB)