Nairobi, September 24 – Toxins in water produced by cyanobacteria killed more than 300 elephants in Botswana this year, officials said on Monday, announcing the result of an investigation into the deaths which had baffled and alarmed conservationists.

More than 70% of the fallen elephants were found near water sources polluted with large amounts of cyanobacteria — a single-cell organism also known as blue-green algae, named for their tendency to clump together in large green mats or “blooms” on aquatic surfaces. These blooms can be hazardous or even deadly, harboring toxins that attack the nervous system, skin or liver of animals exposed to them. Toxic cyanobacteria blooms have previously caused the mass dieoffs of fish, birds and other animals, according to a 2008 study in the journal Global Change Biology.

Not all Cyanobacteria produce toxins but scientists say toxic ones are occurring more frequently as climate change drives up global temperatures.

Southern Africa’s temperatures are rising at twice the global average, according to the Intergovernmental Panel on Climate Change.

“It amounts to having the right conditions, in the right time, in the right place and these species will proliferate,” Patricia Glibert, a professor at the University of Maryland Center for Environmental Science, who has studied cyanobacteria, told news agencies.

“These conditions are coming together more often, in more places, so we are seeing more of these toxic blooms around the world.”

Elephants arrive to drink water in one of the swamps in the Okavango Delta

While no other species seem to have fallen victim to these toxins (save for one horse), it’s possible that the elephants are particularly susceptible because they spend a lot of time bathing in the holes and drinking large quantities of water from them.

Africa’s overall elephant population is declining due to poaching but Botswana, home to almost a third of the continent’s elephants, has seen numbers grow to around 130,000.