aAs soon as the barrier broke, a poisonous flood brought death to the river. In February 2025, more than 50 meters cubic liters of acid and heavy metals leaked through a weak wall built to contain mining waste in Zambia’s copper belt and into the Chambisi River, a tributary of the Kafue River, the country’s longest waterway.
A plume of acid drifted downstream, bringing thousands of lifeless fish to the surface and leaving behind the carcasses of crocodiles and other wildlife.
For the millions of Zambians who depend on Kafue, the collapse of the tailing dam at the Chinese state-owned Sino Metals Reach copper mine has created a national environmental emergency that is far from over. The spill cut off drinking water to Kitwe, Zambia’s third largest city with a population of 500,000 people.
The double quotes looked like diesel mixed with oil. We had already planted crops but they died Mary Milimo
Signs of contamination were detected 60 miles downstream from the collapse. Helicopters tracked the spill downstream and dropped lime into the water to neutralize its corrosive forces.
The affected areas are home to rare wildlife such as the Kafue-lechwe-Zintelope, the Zambian Barbet and the Raven’s Crane.
“It was like a mixture of diesel and oil. We had already planted crops, but they died. Now when we dig up the soil to plant, it is yellowish and has a pungent smell,” said Mary Milimo, 65, a smallholder farmer who lives near where the Mwambasi River joins the Kafue River.
“There are no more fish here,” said Patrick Chindemwa, 66, who farms nearby. “We planted corn using irrigation in October, but all the corn died.
“The ground is yellow and the soil here is like grease. It’s slippery and melts when it rains. We need help,” he says.
Sino Metals did not respond to a request for comment.
Dead fish floating in the Kafue River near the town of Luanshya, Zambia. Water toxicity prevents farmers from irrigating their crops. Photo: Richard Kill/AP
Almost a year later, the Kafue disaster is the latest stain on the mining industry and its long history of environmental disasters caused by improperly stored waste. Tailings dams are repositories for mining waste, often toxic and stored underwater, dumping trash onto landscapes around the world. They often hold large amounts of toxic and harmful substances.
quick guide
What is a tailings dam? What happens if the dam fails?
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What is a tailings dam?
A tailings dam is a structure designed to store mine waste. They last forever. Some are constructed like traditional dams to hold back water, while others are constructed using rock or other waste materials. Some of them are huge, making them some of the largest man-made structures on Earth.
what do they have?
The contents vary depending on the type of mine, but most often contain mud, rocks, and wastewater. However, during the mining process high concentrations of heavy metals and other substances harmful to humans and nature are often unearthed, and these often form part of the contents of tailings dams.
What happens if we fail?
If a tailings dam fails, the consequences can be dire. Large amounts of pollutants can rapidly enter the surrounding environment and contaminate water, soil, and wildlife. In the worst case, hundreds died. In 2019, a tailings dam collapsed near Brumadinho, Brazil, sending a torrent of mud into miners’ canteens and the area below, killing 272 people.
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Although tailing dams are theoretically built to last forever, the increase in extreme weather events due to the climate crisis is changing the risk profile of many structures. Experts say floods, torrential rains and other extreme weather events, many of which are more volatile, mean they increase the risk of future disasters.
Double quotes don’t just disappear. They must be maintained forever…we will be leaving our descendants with huge piles of waste Professor Elaine Baker
An analysis prepared for the Guardian by researchers Tim Werner and Victor Wegner Maus, who have played a leading role in establishing the true scale of the world’s mining industry, found that there are at least 108 tailings dams in key biodiversity areas around the world, a significant underestimate likely due to data limitations. This is approximately 5% of the known tailings facilities registered in the Global Tailings Portal database.
In 2019, a tailings dam collapsed near Brumadinho, Brazil, sending a torrent of mud into miners’ canteens and the area below, killing 272 people. Four years ago, another dam collapsed in Mariana, Brazil, killing 19 people and spreading pollution to more than 600 miles of rivers and waterways. Subsequent research has shown that the invasion caused widespread ecosystem destruction, increasing the risk of extinction for 13 aquatic species and negatively impacting 346 species.
Environmental impacts of tailings dams could last for decades, often with disastrous consequences in nature. Heavy metals do not break down over time and can evolve into many toxic forms, accumulating up the food chain, inhibiting plant growth, and altering soil microbial populations.
Professor Elaine Baker, a marine scientist at the University of Sydney who helped develop the first public database of tailings dams around the world, said: “Our mining methods are still very similar to the Romans. We take a lot of waste and dump it somewhere and hope it doesn’t harm anyone.”
More than 300 people have died after the collapse of the Brumadinho tailings dam in Minas Gerais, Brazil. Photo: Antonio Lacerda/EPA
“They don’t just disappear,” she added. “They have to be maintained forever, so we end up leaving a huge pile of waste to our descendants.
“Dams are inherently more unstable than water dams. We often build dams in valleys, where we build dam walls and dump tailings behind them. They’re some of the largest man-made structures on Earth. When a dam breaks, it creates a slurry of mud that just rolls down the hill,” she says.
Due to the secretive nature of the mining industry, the true global scale of Tailwater Dam is still not fully understood. But it will be extracted in large quantities in coming decades as demand for construction materials and materials needed for the transition to renewable energy increases.
Bora Asuka, a PhD student at the University of Queensland, is researching the scale of tailwater dams in protected areas. Her research found that many are located in critical areas with high biodiversity and are at disproportionate risk of collapse.
Juliet Baraya, a farmer who lives near the Chambisi spill, is surveying damage to her crops and fish ponds. Photo: R Kille/AP
“A surprising 9% of all tailings dams around the world were found to be within protected areas. The majority were created after protected areas were formed. By industry standards, these were also very high-risk tailings facilities,” she says.
Institutional investors such as the Church of England’s pension fund have launched a safety initiative in the wake of the Brumadinho disaster and have called for greater transparency regarding tailwater dams in the mining sector. Together with the Ethics Council of the Swedish National Pension Fund, they brought together investors who collectively oversee $25 trillion (£18.5 trillion) and urged portfolio companies to adopt the highest standards of tailings management.
Illegal and artificial mines also contribute to the problem, with few procedures and even fewer incentives for disposing of mine waste.
Emma Gegen, research director at the International Council on Mining and Metals (ICMM), an industry group that aims to promote sustainable development in the sector, said Brumadinho was a turning point for mining companies in their approach to the Tails dam.
“Any loss of life due to tailings facilities is unacceptable. Standards for conventionally managed tailings have improved significantly,” she said, detailing the 73-point standard developed by the mining industry for best practices in waste management.
A waste trail along the Mwambasi River, a tributary of the Kafue River, after the collapse of a tailings dam at a Chinese-owned mine. Photo: Richard Kill/AP
“It may seem dire,” she says. “I think we’ve really come a long way since the standards were introduced.”
Despite the industry’s efforts, Gergen acknowledged that most mining companies are not members of the ICMM and that the few tailings dams they oversee are likely to meet the council’s standards. This benchmark is designed to adapt to the challenges of more extreme weather events due to climate change, which are expected to put additional pressure on tailings facilities.
Last year, an investigation into the Kafue disaster by Zambian authorities found no evidence that the tailings dam was being maintained by qualified engineers and found cracks and uncompacted walls in the structure. Experts have warned that a similar disaster could occur without drastic action.
“There’s no reason why we see tailing dams in so many conservation areas and conservation areas,” Baker said. “The industry goes wherever it wants to go, wherever it finds deposits. They don’t really care.”
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