As Australia’s northeast region begins to recover from Cyclone Alfred, thousands of fish are washing up dead or dying on the banks of the Richmond River at Ballina in northern New South Wales (NSW), according to charity OzFish.
They’re now asking for help from members of the public to track the extent of a fish kill in a region hit hard by the weather event, which crossed the coast a week ago, causing widespread flooding in that region, as well as southeast Queensland.
Locals have been warned to brace for more fish kills, and an NSW government fisheries spokesperson said an investigation was underway into the reports.
“Fisheries staff are liaising with local councils on monitoring water quality and the fish deaths, with several locations impacted,” they said. “Ongoing fish kills in this region can be expected over the coming days and into next week.”
OzFish wants locals to record and report any dead fish they find so it can understand the scale of the deaths.
Its chief executive, Cassie Price, said black water containing very low oxygen levels was likely the cause.
When organic matter such as dirt and leaf mould is washed into waterways, it turns them a dark colour and strips water of oxygen as it decomposes.
Photos supplied by the charity appear to show fish washed up on the riverbank, while it says it has also received reports of mud crabs and eels emerging from the water to escape the contamination.
Price said the results of water tests carried out by volunteers “aren’t good.”
“Healthy water should have at least 5 milligrams (mg) of oxygen per litre,” she said. “Fish experience distress when it falls below 4 mg per litre and start to die at 2 mg. In the Richmond River today, the dissolved oxygen levels are almost nil, sitting at 0.4 mg.”
People could aid OzFish by recording a pin drop or geo-referencing their location, estimating the number of fish, taking note of any key species they can identify, and taking photos and videos.
Dozens of fish kills are reported in NSW each year, but some events are more devastating than others.
The flooding of the Darling River at Menindee in March 2023 killed an estimated 20 million fish. And earlier this year, a marine heatwave was thought to be the cause of around 30,000 fish being found dead at Gnoorea Beach near Karratha on Western Australia’s Pilbara coast.
Price says that restoring swamplands around the Richmond River would help prevent similar events in the future.
“Urgent action must be taken to prevent further fish kills and build resilience into our waterways,” she said.
