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Water quality monitoring and interpreting the results

Port Macquarie-Hastings Council (PMHC) regularly conducts water quality monitoring for our key estuaries and rivers.  The water quality results are examined in relation to two sets of guidelines;

  • the ANZECC guidelines which are used to provide protection for aquatic ecosystem health (Australian & New Zealand Guidelines for Fresh & Marine Water Quality) and
  • the NHMRC guidelines which are used to provide protection for recreational water use (National Health and Medical Research Council (NH&MRC) Guidelines for Managing Risk in Recreational Waters

Water quality monitoring is conducted at certain sites within the system of interest and tested at PMHC’s NATA accredited laboratory, PMHC examine the results and compare them to the water quality guidelines mentioned above.  The results of our water quality monitoring are regularly published on Councils website.

If the water quality is discovered to be poor, PMHC will ensure the community are made aware of and informed about the results.  Certain protocols have to be followed, in particular with regard to recreational water quality.

Algae, particularly blue-green algae, in recreational waters can pose a health risk to people using these waters for swimming, or paddling or surfing (anything involving immersion in the water or some contact with the water).  The number of blue-green algal cells per millilitre (mL) of water are counted and the following information is used to assess if a risk is present and what action to take:

NHMRC guidelines for managing risks associated with algae in recreational waters: Tables 6.2, 6.3 and 6.6 contain guidance for algae levels.

Table 6.2 Interpretation of blue green (cyanobacterial) alert levels for recreational water

Green level
Surveillance mode
Amber level
Alert mode
Red level
Action mode

≥500 to <5000 cells/mL M. aeruginosa or biovolume equivalent of >0.04 to <0.4 mm3/L for the combined total of all cyanobacteria.

≥5000 to <50 000 cells/mL M. aeruginosa or biovolume equivalent of ≥0.4 to <4 mm3/L for the combined total of all cyanobacteria where a known toxin producer is dominant in the total biovolume.

Or

≥0.4 to <10 mm3/L for the combined total of all cyanobacteria where known toxin producers are not present.

Level 1 guideline:

≥10 μg/L total microcystins

or

≥50 000 cells/mL toxic M. aeruginosa or biovolume equivalent of ≥4 mm3L for the combined total of all cyanobacteria where a known toxin producer is dominant in the total biovolume.

Or

Level 2 guideline:

≥10 mm3/L for total biovolume of all cyanobacterial material where known toxins are not present.

Or

cyanobacterial scums are consistently present.

Table 6.3 Monitoring program associated with cyanobacterial alert levels

Cyanobacterial alert level Monitoring requirement
Surveillance mode (Green level) Routine sampling to measure cyanobacterial levels.
Alert mode (Amber level) Investigations into the causes of the elevated levels and increased sampling to enable the risks to recreational users to be more accurately assessed.
Action mode (Red level) Local authority and health authorities to warn the public that the water body is considered to be unsuitable for primary contact recreation.

Table 6.6 Recommended actions at different alert levels

Level Recommended actions

Surveillance mode (green level)

Regular monitoring:
  • Weekly sampling and cell counts at representative locations in the water body where known toxigenic species are present (ie Microcystis aeruginosa, Anabaena circinalis, Cylindrospermopsis raciborskii, Aphanizomenon ovalisporum, Nodularia spumigena); or
  • Fortnightly for other types including regular visual inspection of water surface for scums.

Alert mode (amber level)

  • Notify agencies as appropriate.
  • Increase sampling frequency to twice weekly at representative locations in the water body where toxigenic species (above) are dominant within the alert level definition (ie total biovolume) to establish population growth and spatial variability in the water body.
  • Monitor weekly or fortnightly where other types are dominant.
  • Make regular visual inspections of water surface for scums.
  • Decide on requirement for toxicity assessment or toxin monitoring.

Action mode (red level)

  • Continue monitoring as for alert mode.
  • Immediately notify health authorities for advice on health risk.
  • Make toxicity assessment or toxin measurement of water if this has not already been done.
  • Health authorities warn of risk to public health (ie the authorities make a health risk assessment considering toxin monitoring data, sample type and variability).

For the protection of aquatic ecosystem health Council uses the ANZECC water quality guidelines

Table 3.3.2 (extraction below) and Table 3.4.1 contain trigger values for south-east Australian ecosystems.  Table 3.4.1 needs to be read from the source (it is too large to attach here).

Ecosystem Type DO Dissolved Oxygen (% saturation) pH Salinity (µScm) Turbidity (NTU)

Freshwater Lowland Rivers

85-120

6-8

20-250

2-15

Estuaries

80-120

7.0-8.5

NA

1-20

Marine Inshore waters

90+

8.0-8.4

NA

1-20

These guidelines tell Council whether the water is optimising ecosystem health and supporting the conservation of aquatic flora and fauna within that particular water system. 

With all Council water quality monitoring advice from experts is always sought in interpreting the results.

This page was last updated on: 09 May 2019