Gaborone, Botswana

In 2020, the world was shocked by the unexplained deaths of 350 elephants in Botswana’s Okavango Delta. While initial investigations ruled out poaching, the exact cause remained elusive for months. A new study led by King’s College London now provides the strongest evidence yet that toxic algae, likely driven by climate change, were responsible for the mass die-off.

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The research, conducted by PhD student Davide Lomeo and co-supervised by Plymouth Marine Laboratory (PML) and the Natural History Museum, points to toxic blue-green algae, or cyanobacteria, as the primary suspect. These algae bloomed in watering holes after a year of heavy rainfall followed by dry ones, creating a toxic environment for the elephants.

The tragic event

The elephants’ carcasses were discovered in the Okavango Delta in May and June 2020. At first, poaching was ruled out, and scientists began investigating other possible causes. While the presence of toxic algae was suspected, a lack of samples due to COVID-19 restrictions made confirmation difficult at the time.

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Study analyses 3,000 waterholes

In their recent study, published in Science of The Total Environment, researchers used satellite data to examine the distribution of elephant carcasses and compare it to the locations of waterholes across the region. The team analysed over 3,000 waterholes and found that those affected by large algae blooms in 2020 had a higher concentration of elephant carcasses nearby. 

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The researchers concluded that the elephants, after drinking from the contaminated watering holes, typically travelled more than 100 kilometres before succumbing to poisoning, usually within 88 hours of drinking the toxic water. 

While similar deaths of elephants in Zimbabwe raised questions about the role of toxins, the new study strongly supports the theory that cyanobacteria in Botswana’s water holes were responsible for the mass die-off.

(With inputs from agencies)