Laboratory results confirm fish kills in Parramatta River were a result of natural processes.
The NSW Environment Protection Authority (EPA), with the help of Department of Planning and Environment scientists, has been testing and monitoring the river all week to understand the causes.
The EPA received reports of dead fish washing up along riverbanks at multiple sites including at Homebush Bay, Wentworth Point, and Ermington.
EPA Executive Director Regulatory Operations Stephen Beaman said investigations showed a combination of factors were responsible for the fish deaths.
"The health of the Parramatta River has improved significantly over the past two decades due to the hard work of the NSW Government, Parramatta River Catchment Group and the community," Mr Beaman said.
"We can see it's home to healthy fish but despite better river health there are still stresses on the river system. "This river condition, combined with repeated heavy rain, large tidal currents and increased amounts of organic matter such as leaves and grass in the river, has reduced the dissolved oxygen available to aquatic life, resulting in the fish kills."
Data from our laboratory confirms:
· Oxygen levels were critically low, especially near the bottom of the river
· Analysis of water samples did not detect any chemical or common organic contaminants such as pesticides that could cause a fish kill
· When re-oxygenated, the water was not toxic
· Examination of the affected fish show no visible effects consistent with either acute or chronic chemical contamination
There is no evidence to suggest this event was caused by a pollution source.
Mr Beaman thanked the community for their response and making reports to the EPA.
"Thanks to all the people who alerted the EPA to the events on the river. It's quite a shock to see the death of so many fish at once."
The clean-up effort continues with City of Parramatta Council and Sydney Olympic Park Authority cleaning up the shorelines while taking special care in sensitive areas such as mangroves and saltmarsh.
Residents are urged not to enter the mangroves or touch the dead fish.
The dissolved oxygen levels in the river are still concerning and the community is encouraged to report any significant number of dead fish sighted on the shorelines to the EPA Environment Line on 131 555.
