Parramatta River fish kills

Information about the results of monitoring the Parramatta River and Haslams Creek after recent fish kills.

In February and March 2022, fish kills were reported at several locations along the Parramatta River and its tributaries. The cause of these fish kills was found to be low dissolved oxygen in the water due to a natural blackwater event.

Fish and other aquatic animals need oxygen to live, and they breathe by filtering oxygenated water through their gills. Unfortunately, man-made and environmental circumstances can result in low levels of oxygen in the water, and if fish are unable to move away from these areas, a fish kill event may occur

Understandably, these events are distressing for the community. The Parramatta River has high amenity, ecological and recreational values. Over time, cooperative efforts by the community, local councils and state government agencies have substantially improved the health of the river, yet as a natural system it remains under pressure from the developed urban environment that surrounds it. Unfortunately, this means that the river is susceptible to blackwater events, particularly in the upper catchment.

Other possible causes of the fish kills

To rule out pesticides and other chemicals as a cause of the fish kills, water was tested for possible contaminants, including common industrial chemicals and heavy metals.  Fish samples taken from the river were not found to contain pesticides.

While sewerage overflows add to the organic material in the river, which increases the chances of blackwater events occurring, bacterial testing of the river water showed that the impact from sewage overflows during the recent wet weather was not high enough to have caused the fish kills.

Installation of monitors

In response to the recent fish deaths, Department of Planning and Environment (DPE) scientists installed several monitors in the Parramatta River to measure the dissolved oxygen in the water. They are located at different sites for different periods of time, depending on the information required.

How the monitors work

The monitors automatically take a reading every 15 minutes of the dissolved oxygen (DO) in milligrams per litre (mg/L), the  temperature (°C) and percent saturation (%). DPE scientists retrieve the monitors to obtain and analyse the data and report to us.


Data was collected from installed monitors from February 7–9 in the Paramatta River and from February to middle of July 2022 in Haslams Creek. Monitors were able to be deployed for longer in Haslams Creek than Paramatta River as the monitors were installed in more easily accessible locations. 

Data shows the dates and times of the levels of DO (mg/L) recorded and other information such as daily rainfall event data. Rainfall data was obtained from the Bureau of Meteorology website relating to Parramatta North (Masons Drive) (Station 066124) weather observations. See more information about weather observation data.

The data is available for download via the link below.

Download the dissolved oxygen data (XLSX 619KB)

Using the information

Information collected from the monitors demonstrates the links between DO and the recent fish kills and is being used to better understand the changes in DO within the Parramatta River and its tributaries. Data from the monitors shows a general trend of lower DO overnight compared to during the day time, with particularly low DO deeper down in the water column at the times of the fish kills. This may explain why species that live at depth appeared to be more heavily impacted than those that live closer to the surface.

Blackwater events are difficult to prevent, but monitoring may play a role in predicting future events and provide forewarning about what may be expected under certain environmental conditions.

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