Healthy Environment, Healthy Community, Healthy Business

Environment Protection Authority

Natural processes lead to fish deaths and odours

Media release: 12 January 2016

Floodplains in the Hunter Valley surrounding local rivers and creeks have been inundated with floodwaters after the recent significant heavy rain which has resulted in a suspected ‘blackwater’ event causing fish deaths and odours.

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

“The recent significant rain resulted in water levels in the Williams, Paterson and Hunter rivers peaking at the same time, increasing the extent and duration of the flooding. 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.

“This natural process is commonly known as ‘blackwater’ and has likely caused the fish deaths and odours in the Hunter River near Raymond Terrace and Hexham. The stagnant water is also contributing to the odours which can smell like rotten egg gas.”

“The hot weather we are currently experiencing is likely to exacerbate these odours and send them further downwind”

“The areas most likely to be affected are Hexham, Motto Farm, Beresfield, Raymond Terrance and Mayfield.”

Mr Davey said the EPA is working closely with the Department of Primary Industries (DPI), Office of Environment and Heritage, Port Stephens Council and DPI Water to monitor the extent and severity of the event.

“The EPA and the Office of Environment and Heritage are taking samples and testing today and tomorrow and results will be released as soon as they’re available.”

The Hunter New England Local Health District advises that all river water in NSW may contain infectious organisms and chemicals, particularly after heavy rain periods.  Entering river water after heavy rain periods increases the risk of injury and infection.  Those who choose to swim in rivers at any time should avoid swallowing water. The Hunter New England Local Health District advises people who may have swallowed river water and become ill, to seek medical advice. 

Contact: Public Affirs

Page last updated: 12 January 2016