Algae bloom kills 350 elephants in Botswana

Satellite data analysis reveals algal blooms may have been responsible for a mass die-off of elephants in 2020.

More than 350 elephants have mysteriously died from drinking contaminated water , according to new research published in the journal Science of the Total Environment. The incident warns of a worrying trend of poisoning caused by climate change . The deaths of elephants in Botswana's Okavango Delta have been described by scientists as a "conservation disaster" . In 2020, hundreds of elephants of all ages walked in circles before collapsing and dying. Their bodies were first discovered in northeastern Botswana in May and June 2020, with many theories surrounding the cause of death, including cyanide poisoning or an unknown disease, according to the Guardian .

Dead elephants littered Botswana in 2020. (Photo: Guardian).

The incident is the largest documented mass death of elephants without a known cause, according to lead author Davide Lomeo, a PhD student at King's College London. The study found that the elephants were poisoned by water contaminated with blue-green algae blooms. The climate crisis is increasing the frequency and severity of toxic algal blooms.

The researchers used satellite data to analyze the distribution of elephant carcasses relative to the waterholes. They were unable to examine the specimens directly due to lack of availability. The team believes that the elephants traveled more than 100 kilometers from the waterholes and died within 88 hours of drinking. In total, they examined 3,000 waterholes and found that the waterholes with increased algal blooms in 2020 had high concentrations of elephant carcasses. According to Lomeo, the elephants had no choice but to drink there. It is possible that other animals died from drinking from the waterholes, but their carcasses were not detected by aerial surveys, and the carcasses of small animals were likely carried away by predators.

That same year, 35 elephants died in neighboring Zimbabwe from a bacterial infection linked to prolonged drought conditions. In 2015, 200,000 saiga antelope died from an outbreak of a blood-borne disease called anthrax in Kazakhstan. Mass die-offs are becoming more common in a warming world, potentially pushing species toward extinction.

In southern Africa, 2019 was the driest year in decades, followed by an extremely wet 2020. These conditions led to a lot of suspended sediment and nutrients in the water, which led to unprecedented algae growth. With climate change, much of the world will become hotter and drier with intermittent heavy rains. The study highlights the need to monitor water quality and take timely action where possible, the experts concluded.