A mysterious mass die-off of more than 350 elephants in Botswana’s Okavango Delta in 2020 has been attributed to toxic water caused by harmful algal blooms, according to a recent study. Researchers warn that the incident underscores an “alarming trend” of climate-induced poisoning, with implications for wildlife conservation globally.
The deaths, described as a “conservation disaster,” involved elephants of all ages displaying unusual behaviour, such as walking in circles before collapsing and dying. First reported in May and June 2020, the event sparked intense speculation, with theories ranging from cyanide poisoning to unknown diseases. The new study, published in Science of the Total Environment, offers the most comprehensive explanation to date, suggesting that climate-induced toxic blooms of blue-green algae (cyanobacteria) in waterholes were the likely cause.
Algal Blooms and Climate Change
Researchers, led by Davide Lomeo, a geography PhD student at King’s College London, used satellite imagery to analyse the distribution of carcasses relative to water sources. Direct water testing was impossible due to the absence of samples. Their analysis indicated that the elephants, after drinking from waterholes with elevated levels of cyanobacteria, typically travelled around 100 kilometres and died within 88 hours. Of the 3,000 waterholes examined, those with increased algal blooms in 2020 corresponded with high concentrations of elephant carcasses.
“Elephants have no choice but to drink from these waterholes,” Lomeo explained. Smaller animals may have also been affected, but their carcasses were less likely to be detected due to predation or decomposition.
The study links the event to extreme climatic conditions in the region. Southern Africa experienced its driest year in decades in 2019, followed by heavy rains in 2020. This combination led to increased sediment and nutrients in water sources, creating conditions conducive to algal growth. As global temperatures rise, such extreme weather patterns are expected to become more frequent, raising the risk of similar mass die-offs.
Broader Implications for Wildlife
This incident is not an isolated case. In the same year, 35 elephants in Zimbabwe died from a bacterial infection linked to prolonged drought, while 200,000 saiga antelope perished in Kazakhstan in 2015 due to a climate-induced outbreak of haemorrhagic septicaemia. These mass mortality events highlight the growing threat posed by climate change to wildlife populations, potentially pushing already vulnerable species toward extinction.
Dr Niall McCann, director of conservation at National Park Rescue, emphasised the significance of the findings: “This study provides a compelling explanation for the mass die-off of elephants that shocked the world in 2020. It adds to the growing body of evidence that climate change can have a range of lethal effects on wildlife.”
Similarly, Dr Arnoud van Vliet from the University of Surrey noted that the research reinforced the established view that cyanotoxins in drinking water were the likely cause. Both experts stressed the need for proactive water quality monitoring and conservation measures to mitigate future risks.
Preventive Measures and Global Lessons
The researchers called for enhanced surveillance of water quality, particularly in regions projected to become hotter and drier due to climate change. As conditions for harmful algal blooms become more common, early detection and intervention could prevent similar tragedies.
The study was a collaborative effort involving scientists from the University of Botswana, the Natural History Museum in London, Queen’s University Belfast, and Plymouth Marine Laboratory. Their findings highlight the intersection of climate change, environmental degradation, and wildlife health, urging a reevaluation of conservation strategies in the face of a warming planet.
While the deaths of over 350 elephants in Botswana represent a significant loss for conservation, they also serve as a stark warning. As climate change reshapes ecosystems, both wildlife and human populations are increasingly vulnerable to its cascading effects.
