Earlier this year, the carcasses of hundreds of elephants were discovered scattered around waterholes in northern Botswana in what was described at the time as a "conservation disaster". The circumstances around the deaths were mysterious: the elephants were found with their tusks still intact, ruling out the possibility that ivory poachers could be to blame, and some of the animals were seen by local witnesses walking around in circles, while the carcasses of others show that they fell suddenly onto their faces just before they perished. Theories around the deaths ranged from natural anthrax poisoning – an option that was eliminated fairly early on – to a bacterial infection.

Botswana government officials have released some findings from their investigation into an unexplained elephant die-off. 

On Monday – some five months after the carcasses were first found – government officials from Botswana finally released some findings from their investigation into the unexplained die-off. They concluded that the elephants died from toxins produced by cyanobacteria. “Our latest tests have detected cyanobacterial neurotoxins to be the cause of deaths. These are bacteria found in water,” Mmadi Reuben, principal veterinary officer at the Botswana department of wildlife and national parks, said in a news conference. “However we have many questions still to be answered such as why the elephants only and why that area only. We have a number of hypotheses we are investigating.”

According to local sources, 70% of the 330 recorded elephant carcasses were found near waterholes believed to contain algal blooms, which typically form when cyanobacteria multiply rapidly as a result of warm, stagnant water that is rich in nutrients. Although not all algal overgrowth can be harmful, in cases where toxins produced in the bloom reach high concentrations they may pose a threat to wildlife, humans and the environment.

Around 70% of the elephant deaths were recorded near waterholes.

Cyanotoxins were initially not thought to be responsible for the elephant die-off, as no other animals – aside from a single horse – were found to be affected in the area. Algal blooms typically impact a variety of species that may have come into contact with the water. Scientists believe that the elephants may be at increased risk as a result of the amount of time the pachyderms spend bathing and drinking large quantities of water. 

Details of the specific toxins detected in the area's waterholes were not disclosed, nor were the names of the laboratories where the samples were tested. Reuben only specified that water samples were analysed in Botswana, South Africa and the US and a "combination of neurotoxins" were found.

Dr Niall McCann, director of conservation at UK-based charity National Park Rescue is hopeful that the findings are accurate: “I hope that what the government has said is true because it rules out some of the more sinister things,” he told told The Guardian. McCann has been critical of the government's slow response to the tragedy which meant that fresh tissue samples were not transported to laboratories for rapid testing. 

“Just because cyanobacteria were found in the water that does not prove that the elephants died from exposure to those toxins. Without good samples from dead elephants, all hypotheses are just that: hypotheses,” according to McCann.

The area in which the elephants were found is home to 10% of Botswana's pachyderm population.

In order to avoid future mass mortalities caused by algal blooms – a phenomenon that will likely occur more frequently and with greater severity as the planet warms up – the Botswana government intends on keeping a close eye on waterholes during the next rainy season. “It is important to monitor now to effectively detect the growth of these algal blooms in the water”, Reuben explained.

In nearby Zimbabwe a similar, albeit less severe, elephant die-off was recorded in August raising concerns that the two incidents may be connected. Authorities have, however, linked this die-off to a bacterial infection, possibly a strain of a bacteria called pasteurella made famous when it wiped out 200,000 saiga antelope in Kazakhstan in 2015. Thankfully fresh samples were collected from the Zimbabwe elephants and have been sent to the UK for testing. 

If the cause of death is something relatively common, scientists should have no problem identifying it. “However, new emerging infectious diseases are happening all the time and the more we look into epidemiology the more we discover we don’t know. So it could be a complete mystery again,” said McCann.