Water quality

Good water quality is vital to ensure the Murray–Darling Basin’s water is suitable for drinking, agriculture, recreation and the environment.

Water management and land-use practices, as well as natural processes, affect water quality in this large and complex river system.

Key facts

More than 2.3 million Australians rely on Murray–Darling rivers and their tributaries for drinking water.

Good-quality water powers $22 billion of primary production across the Basin every year.

Clean, fresh water sustains 120 waterbird species and more than 50 native fish species, many unique to Australia.

Across the Basin, 30,000 wetlands, including internationally significant ones, rely on quality water for their continued existence.

Poor water quality can adversely affect water-based recreational tourism, and the communities that depend on good water quality.

 

Water quality is generally good throughout the Basin but can be compromised by a number of threats, including high salinity, blue-green algal blooms, low dissolved oxygen levels, nutrients, bushfires and turbidity.

Natural events such as droughts, floods and high temperatures can also quickly degrade water quality.

Monitoring water quality

Better natural resource management approaches and techniques are improving this situation across the Murray–Darling Basin.

While natural events that threaten water quality cannot be controlled, monitoring is an important first step in managing water quality issues and potentially reducing their impact.

Water quality targets are in place for managing water flows, water resource planning, and long-term salinity monitoring and management.

Managing water quality will always be a priority in the Murray–Darling Basin.

Water quality threats

Water quality in the Murray–Darling Basin is monitored by individual Basin state governments and specific water quality alerts are issued by respective states. However, the following map provides a snapshot overview of where water quality issues are likely across the Basin.

Threats to water quality

There are many threats to the quality of water in the Murray-Darling Basin’s rivers, lakes and dams.

• Salinity occurs naturally in groundwater, however human practices such as irrigation and land clearing cause water tables to rise, bringing salt to the surface and into rivers. Salinity can affect the health of the environment, reduce drinking water quality, and affect crops and livestock.
• Blue-green algae is found naturally in fresh water, but can be made worse by factors such as elevated water temperatures, sunny days, low flows and increased nutrient loads. Nutrients commonly used in farming such as phosphorus and nitrogen can enter the Basin’s waterways, stimulating algal growth. Combinations of these factors can lead to algal blooms, which pose a risk to both human and animal health.
• Blackwater is a naturally occurring process caused by nutrient rich organic material such as dead leaves and bark washing into rivers during a flood. As this organic matter decays, tannins are released, giving the water a blackish appearance. However, this natural process is not always a threat and is important to the productivity of the river, providing nutrients to supply the food chain that aquatic life depend on. The process can also release chemicals that make water more alkaline or acidic, and can reduce dissolved oxygen levels below critical ecological thresholds, harming or killing fish and other creatures in the river. This is known as hypoxic (low oxygen) blackwater.  
• Low dissolved oxygen levels can occur in drought and flood conditions. Low dissolved oxygen levels suffocate and kill aquatic life (such as fish and shrimps) in large numbers.  In drought, oxygen levels throughout the water column can quickly reduce when stratified water bodies with low oxygen deeper layers rapidly mix with oxygenated surface layers due to sudden changes in weather conditions. In floods with large inputs of organic matter, the process responsible for blackwater can rapidly consume the oxygen in a river or lake to become hypoxic.
• High turbidity is created by issues such as sediment flushed into rivers by erosion, following bushfires, or stirred up by carp. Turbidity reduces the penetration of sunlight, affecting plants and aquatic life.
• Temperature variations in rivers created by cold water released from dams, or summer heatwaves can be harmful to plants and aquatic life. Warm temperatures also encourage blue-green algae growth.
• Acid sulfate soils do not present any risk if left submerged, however when exposed to oxygen such as when water levels fall, acidification can occur. A complex series of reactions produce sulfuric acid, release heavy metals, drop oxygen levels and in extreme situations can create conditions resulting in the death of fish and other aquatic life.

Measuring water quality

The presence of contaminants and the characteristics of water are used to indicate the quality of water. These water quality indicators can be categorised as:

• Biological – bacteria, algae
• Physical – temperature, turbidity and clarity, colour, salinity, suspended solids, dissolved solids
• Chemical – pH, dissolved oxygen, biological oxygen demand, nutrients (including nitrogen and phosphorus), organic and inorganic compounds (including toxicants)
• Aesthetic – odours, taints, colour, floating matter

Measurements of these indicators can be used to determine and monitor changes to water quality for drinking water, stock and domestic purposes. These measurements can also determine if water is suitable for the health of the natural environment and its specific uses.

Managing water quality

Managing flows, wherever possible, can help to mitigate salinity, turbidity, fluctuating water temperature and dissolved oxygen.

Water quality is managed in partnership by the Australian Government and the Basin state and territory governments.

At the local level, communities and landholders are working together, with the Murray–Darling Basin Authority and local and Basin state governments, to reduce salinity and improve water quality.

Water resource plans are required to include water quality management plans. These plans identify key causes of water quality degradation and risks to water quality and incorporate water quality and salinity targets. They also specify cost-effective measures to be undertaken to achieve water quality objectives.

Water quality targets are set out in the Murray–Darling Basin Plan, the Murray–Darling Basin Agreement and the Water Quality Guidelines under the National Water Quality Management Strategy.

The Murray–Darling Basin Authority annually assesses performance against water quality targets and evaluates Basin Plan water quality outcomes every 5 years.

Basin governments apply an adaptive management approach to water quality, using new information, trialling techniques and making changes as needed.