Issues affecting water quality

​​​​​Maintaining good water quality is essential to human health, the environment, agricultural industries and the recreational value of waterways, wetlands and coastal waters.

Awareness of the environmental conditions and human activities that influence water quality is an important part of effective water management.

Strategies for managing these issues are developed by state and territory governments, local government councils and shires, or regional organisations such as natural resource management bodies, supported by national guidance contained in the National Water Quality Management Strategy (NWQMS).

Water managers and jurisdictional agencies can:

Acid sulfate soils

Acid sulfate soil is the common term for soil that contains naturally-occurring chemical compounds known as metal sulfides. When soil containing metal sulfides is exposed to air it can pose a risk to water quality by releasing acid and other contaminants, such as heavy metals, into waterways and wetlands once rewetted. This causes a reduction in pH and dissolved oxygen levels.

Guidance is available to help jurisdictional water and land managers identify and manage acid sulfate soils. The guidance provides information to prevent, minimise, mitigate and remediate the harmful effects that disturbance of acid sulfate soils can have on water quality, aquatic ecosystems, farming and fishing, and built infrastructure.

Resources for managing acid sulfate soils

Blackwater events

Blackwater events are a natural feature of lowland river systems and occur when a build-up of leaf litter and debris on floodplains is washed into waterways during flooding. The high amount of organic material in the water is then consumed by bacteria, depleting dissolved oxygen in the water.

Managing the effects of blackwater events is the responsibility of jurisdictional water authorities and land and water managers. Although backwater events can cause localised fish kills, they also serve to redistribute essential organic matter and nutrients through the landscape.


Bushfires can affect water quality particularly when there is heavy rain immediately after a fire has occurred. Altered soil structure and loss of vegetation cover in the aftermath of a fire can increase the risk that sediments and pollutants will run off into waterways.

Drinking water, water for agricultural activities and local aquatic ecosystems can be negatively affected by rapid surface-water runoff after bushfires.

Primary responsibility for the management of these risks is at the state and territory, regional and local level, where it is important for authorities to minimise the threat of intense bushfires and respond quickly after a major fire to stabilise the soils and facilitate natural recovery of vegetation.

In late 2009, the Australian Government commissioned The University of Melbourne to conduct a review of existing literature on the impacts of bushfires on water quality​ in Australia. The review considers the water quality impacts of bushfires on various uses and values, including drinking water, aquatic ecosystems and agriculture, and recommends management actions for before, during, and after a fire to minimise impacts on water quality.

Cyanobacteria (blue-green algae)​​​

Cyanobacteria (blue-green algae)​​ are microscopic, algae-like bacteria that bloom in still or slow flowing water, where there is abundant sunlight and high nutrient levels.

Blooms can occur in freshwater, coastal and marine waters.

Risks to human and livestock health, agriculture and the environment posed by blue-green algae make it a priority issue for water quality managers, jurisdictional agencies and the Australian Government.​


Salinity refers to the level of salts in soil or water, and is a natural feature of the Australian landscape. Human activities including vegetation clearance, poor land management and irrigation practices can increase salinity levels in soils or waterways.

Management of salinity, and the human activities that contribute to it, are planned and enacted by jurisdictional water authorities and land and water managers.

Urban catchments

Cities and urban areas produce large volumes of runoff that needs to be appropriately managed.

The quality of urban stormwater can be significantly impacted by point and diffuse sources of contamination from industry and transport, water treatment facilities and residential homes.

Urban water catchments tend to have large areas of impervious surfaces such as roads, rooftops and pavement which:

  • increase the velocity of water flow
  • inhibit ponding and the infiltration of water into soil.

Urban streams are an important feature of our cities and suburbs and play a major role in stormwater management and flood control. While these streams tend to be modified or engineered, they are an important part of the urban landscape providing valuable recreation, aesthetics and biodiversity conservation areas.

During rainfall events, stormwater flows can rapidly enter urban streams carrying high levels of nutrients, sediment and heavy metals. This produces water with high biological oxygen demand (BOD) and low dissolved oxygen levels. Rapid changes in water quality can affect receiving aquatic environments, such as coastal waters, estuaries, rivers and wetlands.

Effects on aquatic environments include:

  • outbreak or establishment of invasive aquatic species
  • smothering of aquatic plants
  • toxicity to aquatic organisms
  • closure of recreational access due to the introduction of pathogens, the promotion of algal blooms or other contamination issues such as odours, harmful skin reactions and visual amenity.

As urban development in Australia grows, along with increasing demand for fit for purpose water for a wide variety of uses, managing urban water quality will present an increasingly complex challenge for governments and the community.

The NWQMS has 3 guidelines relevant to the management and use of urban stormwater:

  • Urban stormwater management provides a nationally consistent approach for managing stormwater in an ecologically sustainable manner. Water managers can use the guidelines to:
    • identify objectives for stormwater management
    • integrate management activities at the catchment, waterway and local development level.
  • Water recycling — augmentation of drinking water supplies covers the use of recycled water (including stormwater) to boost drinking water supplies.
  • Water recycling — stormwater harvesting and reuse provides guidance on managing potential public health and environment risks associated with the reuse of:
    • roof water collected from non-residential buildings
    • urban stormwater from sealed areas, including drains waterways and wetlands.