Learn about series
A series of information pages on the basics of water.
What is bad water quality?
Sometimes water in a river or stream can be poor quality. This means it can make us sick, it may not be good for our crops, and sometimes fish and other aquatic animals become sick or even die.
The quality of water in our rivers is dynamic and varies with time and location. Both natural factors and human activities can affect water quality.
Natural factors that can affect water quality include the local geology, climate, vegetation and stream flow. There are also a wide range of human practices that may change water quality. This includes sewage discharge, mine waste, land clearing, and urban and agricultural development.
What is bad water quality?
At times, both natural events and human activities can cause poor water quality in surface water environments. This video explores three types of poor water quality.
What are some common types of bad water quality?
There are 3 key types of poor water quality that affect surface water sources in NSW:
- Algal blooms
- High salinity
- Hypoxic water
Algal blooms
Algae are photosynthetic organisms that are an important part of healthy river systems. They are known as primary producers and form the base of the aquatic food web.
Algal blooms can occur when algae multiply very quickly, particularly when it is warm, or when a river stops flowing and disconnects into pools. Algal blooms can cause discolouration of the water, and may look like scum on the water surface.
Algal blooms caused by blue-green algae can produce toxins that can harm people and animals if consumed. They can also be harmful for humans to come into contact with, making swimming and recreational activities unsafe.
High salinity
Salt is a natural part of the landscape of NSW and some rivers have naturally high salinity levels. However, human activities such as vegetation clearing, intensive irrigation, and discharge of saline wastewater can speed up the release of salt into soils and water sources.
Low or no flows can also cause salinity levels to increase, as salt builds up in disconnected pools by evaporation.
High levels of salts in water can be harmful to plants and not suitable for animals to drink. Salt can make it expensive to treat drinking water and may mean water can't be used to irrigate crops.
Hypoxic water
Hypoxia means low oxygen. When water sources like rivers or lakes have very low oxygen, we say they have hypoxic water.
At times, the water at the bottom of a pool can become colder and have a lower oxygen content than the rest of the pool. If the weather changes, this low oxygen water can suddenly mix into the rest of the pool. Fish and other aquatic animals rely on oxygen in the water to survive. Sudden drops in oxygen can cause them to become sick, or even die.
Hypoxic water also occurs when bacteria break down large amounts of organic matter, such as dead leaves, grass, bark and sticks and consume oxygen faster than it can be replaced from the atmosphere. This can occur during major flooding and is sometimes referred to as a hypoxic blackwater event.
Why is water quality important?
Our rivers and streams are of major environmental, social, cultural and economic value.
Clean water supports drinking supplies, recreational activities, and plant and aquatic life. It also ensures the productivity and safety of agriculture, which relies on clean water for irrigation and livestock.
Water is also an important part of First Nations culture. First Nations people rely on clean river water to carry out cultural traditions and maintain a connection to Country.
Poor water quality can harm the health of our communities, industries, and ecosystems. It’s important we work to avoid poor water quality in our rivers.
How is water quality managed?
Many different factors can cause poor water quality, which can make it complex to manage. In most locations, there are no flow options available to address a critical water quality event.
Diverting river flows carrying large amounts of plant material away from pools can help prevent water from becoming hypoxic. However, these flows can also be a great source of nutrients for organisms in our rivers, which then increases food availability for larger aquatic animals such as fish and turtles. There also needs to be a dry floodplain or wetland nearby that we can divert the flow containing the organic matter to, meaning this option is not always available.
In catchments where there is a water quality allowance available, we can release water from upstream storages to dilute hypoxic water, dilute high salinity or flush algal blooms.
To prevent high salinity levels, we can use pumps that divert salty groundwater away from rivers and into evaporating basins. Because human activities at the surface can increase the level of salt entering our rivers and creeks, it is important that salinity risks are considered in both land and water management.
While we can’t always avoid bad water quality, we can minimize the risk by managing our rivers effectively. We work hard to maintain adequate river flow, keep rivers connected, and keep water quality clean and safe.
How is the department responsible?
Over 30 agencies and organisations play a role in monitoring and managing water quality in NSW. The department’s Water Group works closely with many of these agencies to keep our rivers and streams healthy, and respond to issues such as hypoxic water, high salinity levels, and algal blooms.
The department publishes updates on water quality stages for hypoxia on our website.
Current algal alerts are published by WaterNSW.
We also monitor salinity levels in areas such as the Murray-Darling Basin and have a role in salt interception schemes in south-western NSW.
We have also developed the Water Quality Governance Roadmap, which outlines how NSW is improving the governance of water quality. This includes clarifying roles and responsibilities, and improving coordination of agencies who manage water quality.
How can you help?
If you notice changes in water quality in your local waterway, such as changes in colour or odour, you can report it via the NSW DCCEEW enquiries (water.enquiries@dpie.nsw.gov.au).
To report dead fish or fish struggling or gasping at the water surface call the Fishers Watch Phoneline on 1800 043 536. You can also contact WaterNSW to report an algal bloom.
Learn in more detail about water quality of surface water environments