A new study suggests that over 350 elephants that died mysteriously in Botswana’s Okavango Delta likely drank water contaminated by toxic blooms of blue-green algae, or cyanobacteria. This event, which has been described as a “conservation disaster,” occurred in May and June 2020, with elephants of all ages observed walking in circles before collapsing and dying. Initially, there were various theories about the cause, including cyanide poisoning or an unknown disease.
The incident was the largest recorded elephant die-off where the cause was initially unknown, sparking significant concern. According to lead researcher Davide Lomeo, a geography PhD student at King’s College London, this uncertainty is what made the event particularly alarming. The new paper, published in Science of the Total Environment, proposes that the elephants were poisoned by drinking from waterholes affected by harmful algal blooms, which have become more intense due to the climate crisis.
Using satellite data, the researchers mapped the distribution of the elephant carcasses relative to watering holes and found that the elephants likely drank from waterholes within 100 kilometers (62 miles) of their location before dying within 88 hours. The team analyzed 3,000 waterholes and found that those with increased cyanobacteria blooms in 2020 had a higher concentration of elephant carcasses. While it’s possible other animals also died from drinking the contaminated water, their remains may not have been spotted during aerial surveys.
This mass die-off highlights the growing trend of sudden, climate-induced diseases. In the same year, 35 elephants in neighboring Zimbabwe died from an obscure bacterial infection linked to prolonged drought conditions. Other incidents, such as the mass death of 200,000 saiga antelope in Kazakhstan in 2015 from a climate-linked outbreak of blood poisoning, underscore the rising frequency of climate-related mass mortality events, which could push species to the brink of extinction.
The climate crisis, marked by extreme weather conditions like droughts followed by heavy rains, creates ideal conditions for harmful algae growth. In southern Africa, 2019 saw the driest year in decades, followed by an exceptionally wet 2020, leading to increased sediment and nutrients in the water, fueling unprecedented algal blooms. As the climate warms, the region is expected to experience hotter and drier conditions with intermittent heavy rains, which could lead to more frequent occurrences of such deadly outbreaks. Lomeo emphasized that these events serve as a warning that such climate-induced diseases could affect any animal in the future.
Dr. Niall McCann, director of conservation at National Park Rescue, called the study a compelling explanation for the 2020 elephant die-off, noting that it adds to growing evidence that climate change is having lethal effects on wildlife, livestock, and humans. Dr. Arnoud van Vliet from the University of Surrey also supported the study’s findings, affirming the view that cyanotoxins in drinking water contributed to the mass deaths.
The researchers stress the need for water quality monitoring to prevent similar incidents in the future, particularly as the southern African region faces drier and hotter conditions. The study was conducted in collaboration with several institutions, including the University of Botswana, the Natural History Museum in London, Queen’s University Belfast, and the Plymouth Marine Laboratory.
