In 2020, a mass die-off of 350 endangered African elephants in Botswana made headlines. There have been several theories as to what caused the deaths, but a new study finds it was likely due to harmful algal blooms, which can worsen with climate change.

Researchers at King’s College London recently used satellite data, spatial analysis, and water health data to gauge the link between where the elephant carcasses were found during the 2020 mass death event and the state of about 3,000 waterholes nearby. According to the findings, published in the journal Science of the Total Environment, the carcasses were found near waterholes that were experiencing significant harmful algal blooms at the time of the deaths. This raises concerns about yet another way our changing planet is seriously impacting wildlife.

Davide Lomeo, the study’s lead author and PhD student in King’s College’s Department of Geography, says, “Botswana is home to a third of all African elephants, and this unprecedented die-off within their largest remaining population underlines the escalating concerns surrounding the impact of drought and climate change on the Okavango Delta, one of the most important ecosystems in the world.”

The delta was where carcasses were first discovered in 2020. The research showed that 20 waterholes in the area, and located near the dead elephants, had significantly more harmful algal bloom events in 2020 than there were in the prior three years combined. This means there were likely toxins from the blooms in the water.

According to the United States Environmental Protection Agency, climate change may increase the likelihood and severity of harmful algal blooms for a variety of reasons. First is that the blooms thrive in warmer water. Second is that higher carbon dioxide levels in the water promote their growth. Another key factor is that increased rainfall can lead to more runoff in the water, including nutrients that are favored by the blooms. Drought can also keep them there longer.

In 2020, the region where the die-off occurred was experiencing a very wet year, following a very dry year, which researchers believe may have brought up large amounts of sediments and nutrients from the ground.

The U.S. Centers for Disease Control and Prevention says when animals consume the toxins in harmful algal blooms, they can experience serious symptoms including vomiting, diarrhea, stumbling and falling, and tremors and seizures.

The study showed that the elephants traveled an average of more than 10 miles after likely drinking from these contaminated water sources, and they may have died within four days, possibly suffering from the aforementioned symptoms.

The researchers say their study provides strong evidence that harmful algal blooms killed these endangered animals, which they argue shows that studying water quality during animal mortality events may help mitigate such deaths and inform conservation strategies.

Lomeo says, “Southern Africa is projected to become drier and hotter under climate changes, and as a result waterholes across this region will likely be drier for more months of the year. Our findings point to the potential negative effects on water quantity and quality, and the catastrophic repercussions on animals, this could have.”