Healthy Environment, Healthy Community, Healthy Business

Environment Protection Authority

Hunter 'Blackwater' Event - Update

Media release: 19 January 2016

The EPA has received the results of scientific studies conducted by the Office of Environment and Heritage (OEH) which provide strong evidence of the likely source of the recent fish deaths and odours in the Hunter.

Floodplains in the Hunter Valley have been inundated with floodwaters after the recent significant heavy rain which has resulted in a blackwater event causing fish deaths and odours.

Gary Davey, EPA’s Director North said the odours around Newcastle are caused by natural processes due to low levels of oxygen in the Hunter River.

“As the floodwaters moved over low lying areas surrounding the rivers, they picked up large quantities of organic matter, including decaying vegetation, leaves, dirt and sand. 

“Although an important process for healthy river function, the decomposition of this organic matter depletes oxygen levels in the water and releases tannins which give the water a distinctive black colour.”

The most recent data gathered by the Office of Environment and Heritage (OEH) since the floods show that dissolved oxygen (DO), which is vital to supporting aquatic life, is at some of the lowest levels reported in recent years, and that the Williams and Paterson Rivers were also contributors to the blackwater.

Healthy DO levels in rivers and estuaries vary between 70 – 100%, depending on water quality and temperature.

The data from river sampling conducted by OEH in the Hunter catchment showed DO levels were extremely low (1-2% DO) in these rivers for several kilometres upstream from their confluence with the Hunter River. DO levels started to increase in upper stretches of the Hunter River upstream of the Williams and Paterson rivers and reached 45% DO at Morpeth.

Hunter River water showed 1-2% DO from Tomago to Raymond Terrace. These low levels are from surface waters to the bottom. This equates to over 40km of blackwater in the system, which will slowly work its way to the mouth of the river. 

Gary Davey said there is no evidence to suggest any linkage between recent mine dam incidents in the upper Hunter catchment and the blackwater event in the lower reaches of the Paterson, Williams and Hunter Rivers.

“Firstly, there are no coal mines in either the Paterson or Williams River catchments.

“Testing also shows that Dissolved Oxygen levels in waters coming down the Hunter River were considerably higher than the DO levels in the area where the fish kills occurred, for example 40% at Morpeth and 1% at Raymond Terrace.

“Assessment of salinity data from upstream to downstream has also identified that saline water discharged from mines as part of the Hunter River Salinity Trading Scheme has not caused the fish deaths.

“Unfortunately, it will be still some time before the impacts of the blackwater event dissipate and the river starts to return to normal. We have requested councils to conduct clean-ups of the dead fish, but in the meantime, the community is reminded to continue to exercise caution around the river and any stagnant waters.”

EPA and OEH will continue testing waters and monitoring the blackwater over the coming days.


Contact: Public Affairs

Page last updated: 19 January 2016