The mysterious deaths of 350 African elephants has plagued Botswana wildlife authorities for months.
Hundreds of the massive animals apparently dropped dead in the Okavango delta in late May.
Their tusks were untouched. With no sign of foul play or anything to link these deaths, the theories of disease or poaching were dismissed.
Botswana is home to 130,000 African elephants, the largest population on the continent. Last year there was outcry when the country repealed a ban on hunting elephants, which had been in place since 2014. However the mystery elephant deaths showed no sign of either illicit or legal hunting.
Over 330 animals were found to have died in Botswana, with other cases in neighbouring Zimbabwe.
However the baffled conservationists my have found the culprit of these mass elephant deaths, at the bottom of dried up puddles.
Traces of toxic algal blooms were discovered in dry watering holes. Home to microscopic 'cyanobacteria', it is possible the elephants may have been uniquely vulnerable to the poison. 70 per cent of the elephant carcasses were discovered near watering holes.
In smaller doses the poisonous algae is normally not enough to kill most animals, however findings suggest it could eventually be lethal for animals which drink large quantities of water and spend much of their time bathing. Animals such as elephants.
With the exception of one horse, reported by Africa Geographic, it was only elephants which fell victim to the mysterious killer.
The analysis of the elephant epidemic was further complicated by the sensitivity of the data. The illegal ivory trade is rife in this part of the continent, and ministry workers had a huge job to extract and destroy the tusks of carcasses "within proximity to human settlements," said KD Maselesele, secretary for the Botswana ministry of natural resources.
"The ongoing investigations, into the deaths of the elephants, have revealed no evidence of poaching so far."
Laboratories Zimbabwe, South Africa and Canada helped study the mysterious deaths concluding that "commonly used agro-chemicals or pesticides have been ruled out as the cause of mortality." As was the theory that the elephants had suffered some sort of pachyderm plague, with "infectious pathogens unlikely to be the cause of death."
While the discovery of neurotoxins and poisonous bacteria is a breakthrough, some conservationists remain skeptical reported The Guardian.
"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," said UK-based conservation director Dr Niall McCann of National Park Rescue.
Other countries are using the findings to examine their own unsolved animal deaths from this year, such as neighbouring Zimbabwe in which over 20 elephants were found dead.