“Welcome to dead fish central,” said Graeme McCrabb, a local resident, as he navigated his speedboat through fields of rotting fish carcasses bobbing in the acid-green water of the river that runs through his town.
Millions of fish have died in the Darling River near his town, Menindee, in outback New South Wales, their bodies packing the surface of the water from bank to bank for miles. After days under the sun, their bodies had started to “break up and turn into fish soup,” as Mr. McCrabb put it, transforming the river that locals rely on for drinking and showering into an ecological wasteland.
Authorities have said the mass death was caused by a lack of oxygen in the water, called hypoxia, a result of recent floods and a heat wave. But furious locals say the true root of the problem is the overuse of Australia’s biggest and most vital river system.
The disaster is the latest episode in a long-running battle over the Murray Darling Basin, a vast network of lakes and rivers stretching across four states in eastern Australia, which sustains much of the country’s agriculture and dozens of communities along its banks. In an arid country where social, economic and environmental interests clash whenever water runs scarce, the issue has pitted states against each other, and riverside communities against farms upstream.
In Menindee — population: 551 — residents have endured the stink of decaying fish for several days. At its worst, one resident, Barry Stone, described it as “eye-watering. It stung the inside of your nose and made you want to throw up.”
And they fear for their drinking water, which is treated river water.
More frustratingly, they said, is how they have been raising concerns about the declining health of the river for years, to little avail. Even after a previous mass fish death in 2019, little was done to address the problem, they said.
Out on the river on Wednesday, Mr. McCrabb pointed out various species of dead fish: bony herring, gold perch, endangered silver perch, some invasive species. Five days into the die-off, fish corpses had started drifting downstream with the current and sinking to the bottom. Decaying skin and flesh had disintegrated into flakes, creating films of gray sludge on the water’s surface.
Crayfish covered in this film tried to escape up the sides of the steep riverbank, while the occasional live fish jumped out of the water or flailed near its surface, gasping. The initial die-off had further depleted oxygen in the water, causing more fish to die. Carp, which endure low-oxygen environments better than other fish, swarmed around the carcasses, thousands of tiny mouths opening and closing incessantly at the water’s surface.
Mr. McCrabb, a grape grower, has become an unofficial face of the disaster. During both the 2019 fish death and the current one, he has regularly taken his boat onto the water, documenting the carnage to raise awareness — and “rub salt in the wounds of the government,” as he puts it.
He is not the only one in the area to become an accidental activist. In Menindee, as in other towns along the river, small-business owners, retirees and Indigenous people traditionally associated with the area have mobilized in the face of what they see as an existential threat to their communities and livelihoods.
“You can put a time limit on the river,” said Ross Leddra, a Menindee resident and the president of the Darling River Action Group, a coalition fighting for better-quality water. “They’re saying in five to 10 years the river will be dead.”
Even though locals knew another fish death event was possible, “no one thought this would ever happen to this extent,” he said. “How are they going to repair the river when there’s millions of dead fish on the bottom decomposing into the soil?”
Authorities have called the cleanup a “logistical nightmare,” acknowledging that it will be impossible to completely remove the carcasses because of the scale of the disaster.
“I need to be very upfront with the community in saying: Will every fish be removed? I don’t think so,” said Brett Greentree, the state police assistant commissioner overseeing the effort.
Standing outside his home on the riverbank, Ross Files, a retiree, watched fish floating in the same water he used for bathing and laundry, and contemplated how long he might be able to continue living by the river.
“I think it’s the finish of me,” he said.
Mr. Files, 85, said that in his youth the river water was clean enough to drink from without treatment. He is one of many residents who say the river’s health started to decline when agriculture intensified upstream a few decades ago, leaving less water available to flow downstream.
“This problem didn’t start yesterday or last week or last year,” he said. “I’ve been here for 85 years, and for the last 25 I’ve had nothing but problems with the river.”
Some scientists share this view. The 2019 fish deaths happened during a drought and the current ones after a flood, said Richard Kingsford, the director of the Center for Ecosystem Science at the University of New South Wales. But, he said, the long-term causes were the same both times: “There’s not enough water in the river, and the whole system is engineered so these escape routes are closed.”
Over-extraction means parts of the river run dry more often, he said, and the small and medium-sized floods that used to periodically clear away organic debris have all but disappeared. That means when a big flood hits, that debris is all swept into the river, where it breaks down and deoxygenates the water.
That, combined with the construction of weirs that have prevented the fish from swimming to better-oxygenated water, has made this disaster worse, he said. He adds that while fish organically breed and die en masse, natural processes alone cannot explain the extraordinary scope of the recent fish deaths.
The New South Wales fisheries and water management bodies, by contrast, both attribute the disaster to weather-related causes. “For a natural event such as this, there are very few operational steps that can be taken to prevent them from occurring,” WaterNSW, which manages the state’s rivers, said in a statement.
Issac Jeffrey, chief executive of the National Irrigators’ Council, echoed this sentiment. “It’s awful to see, but it is part of the cycle,” he said via email.
On Thursday, after many of the fish had already sunk to the bottom of the river, the cleanup started with workers in small boats removing floating carcasses with hand-held nets.
Authorities said this will be followed by machinery that will drag nets through the river to scoop up sunken fish.
But to Mr. McCrabb, it seemed like a futile effort, considering how many days the fish carcasses had already been decaying and sinking in the water.
It was impossible to clean up a disaster this enormous, he said. “The only way to deal with it is to prevent it.”