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Water quality

Maintaining the quality of water is crucial for a healthy environment and for providing suitable drinking water for communities. Water quality may also impact the productivity and profitability of agricultural activities, and recreational use of our waterways.

Land management and land-use practices are key causes of water quality degradation in the Murray–Darling Basin. Major indicators of a decline in water quality are salinity, low dissolved oxygen (including blackwater), water temperature, blue-green algae, suspended matter, toxicants, nutrients and pH levels).

We can minimise the effects of physical, biological and chemical threats on the quality of the Basin's water, by carefully managing the water resources of the Murray–Darling Basin.

Low water levels in the Hume Dam, New South Wales.

Threats to water quality

These water quality threats include:

  • High salinity – large quantities of salt occur naturally in the Murray–Darling Basin, but salt mobilisation into the Basin's water resources is often increased by activities such as irrigation development and land clearing. Excessive salinity can affect ecosystem health, reduce drinking water quality and cause economic loss in irrigated agriculture.
  • Cyanobacteria (blue-green algae) blooms generate toxins that can pose a serious health risk to humans and livestock.
  • Nutrients (including phosphorus and nitrogen) deposited into the Basin's waters by agricultural activity, stormwater and erosion can stimulate algal growth.
  • Turbidity is caused when matter suspended in water reduces light penetration, which can affect aquatic plants and animals.
  • Temperature – during summer, releases of water from deeper layers held in dams can cause lower water temperatures, which can damage downstream ecological communities. Higher temperatures, resulting from lack of flow and/or from clearing of vegetation at the edges of rivers, creeks and lakes, may worsen an algal bloom and adversely affect aquatic ecosystems.
  • Dissolved oxygen – low levels of dissolved oxygen can come about when floodplains are inundated. Microbial breakdown of the organic matter can quickly consume the oxygen, resulting in what is described as a 'blackwater' event. This can also cause fish death. Releases from deeper layers in a dam, river or lake in summer may also contain low levels of dissolved oxygen, which is harmful to many aquatic organisms

Water quality targets

The Basin Plan (Chapter 9) sets out a series of water quality targets to help ensure the Basin's water is suitable for drinking, agricultural, recreational and environmental purposes.

The water quality and salinity management plan provides:

  • Targets for managing water flows –dissolved oxygen, blue-green algae and salinity.
  • Targets for water resource plans –targets for fresh water-dependent ecosystems, irrigation water and recreational water.
  • Targets for the purposes of long-term salinity planning and management –surface waters of rivers and tributaries.

Managing water flows

  • To maintain dissolved oxygen at a target value of at least 50% saturation (at 25°C and atmospheric pressure).
  • For recreational water, that the total biovolume for blue–green algae (cyanobacteria) should meet the guideline value set out in the guidelines for managing risks in recreational water.
  • The levels of salinity at the reporting sites mentioned in the following table should not exceed the values set out in the table 95% of the time.
Reporting site Target value (EC) (µS/cm)
River Murray at Murray Bridge 830
River Murray at Morgan 800
River Murray at Lock 6 580
Darling River downstream of Menindee Lakes at Burtundy 830
Lower Lakes at Milang 1,000

Performance against the above targets are assessed annually by the Murray–Darling Basin Authority.

Water resource plans

Water resource plans (WRP) being developed under the Basin Plan include a water quality management plan (WQM Plan). This will encourage water planners to consider the impacts that wider natural resource management and land management activities may have on water quality within their WRP area.

WQM Plans will identify key causes of water quality degradation and risks to water quality, incorporate water quality and salinity targets, and seek to provide the same or better levels of protection as those set out in the Basin Plan.

The provisions in the Basin Plan link development of the WQM Plans to the objectives and targets in Chapter 9, including setting out alternative targets where necessary, and providing reasons why alternative targets would be more appropriate for a particular WRP area.