Toxic Algae Confirmed as Cause of Mass Elephant Deaths in Botswana

A new study has definitively linked the deaths of at least 350 elephants in Botswana’s Okavango Delta in 2020 to toxic algae, Al Jazeera reports.

Researchers from King’s College London, collaborating with the Plymouth Marine Laboratory and the Natural History Museum, found that cyanotoxins, produced by cyanobacteria (blue-green algae), contaminated around 20 watering holes across a vast 6,000 square kilometer area.

The discovery followed an investigation triggered by aerial surveys conducted by Elephants Without Borders in early to mid-2020. These surveys revealed a shocking number of elephant carcasses and bones scattered across the Ngamiland district. The spatial clustering of the remains suggested a rapid, localized cause of death rather than a gradual decline. The absence of poaching evidence (tusks were intact) ruled out human involvement. Initial theories involving infectious diseases like anthrax and encephalomyocarditis virus were also dismissed due to the lack of clinical signs in the deceased elephants.

The research team, led by Earth observation scientist Davide Lomeo, used satellite imagery to analyze the location of the carcasses and the distances elephants traveled after drinking from various water sources. The data revealed that elephants died an average of 3.6 days (88 hours) after drinking from contaminated water holes, a timeframe consistent with known toxicological effects of blue-green algae poisoning in other mammals. The average distance the elephants traveled after drinking was 10.2 miles.

While the evidence strongly points to toxic algae as the primary cause, the researchers acknowledge some limitations. The COVID-19 pandemic hampered timely tissue sample collection, preventing definitive confirmation of cyanotoxins in the elephants’ bodies. Furthermore, the precise toxicity levels in each waterhole couldn’t be measured remotely. It remains unclear whether the elephants drank from multiple contaminated sources or if a single event caused the fatal intoxication. The possibility that other animals may have also been affected, but were removed by scavengers, also cannot be ruled out completely.

Despite these uncertainties, the Botswana government has officially attributed the mass die-off to environmental intoxication by cyanobacterial toxins. The researchers warn that similar events could occur in other arid regions where animals depend on stagnant water sources. Further research is needed to fully understand the specific environmental conditions that create lethally toxic algal blooms and the broader implications for wildlife and ecosystems.