Cyanobacteria in water resulted in the mysterious death of hundreds of elephants around the Okavango Delta in earlier this year, Botswana's Department of Wildlife and National Parks (DWNP) senior officials said on Monday.

Principal veterinary officer in the DWNP Mmadi Reuben said neurotoxin producing cyanobacteria species was responsible for the deaths of some 330 of jumbos.

When this occurred tests were conducted at specialist laboratories in neighbouring South Africa, Zimbabwe, the U.S. and Canada. 

"The deaths were caused by poisoning due to cyanobacteria which was growing in pans," Reuben said. He also said mortality stopped towards the end of June 2020, coinciding with the drying of pans.  Botswana's elephant population is estimated at around 130,000.

Deputy director of DWNP Cyril Taolo said anthrax and human involvement were ruled out.

"We cannot talk about human involvement in these cases," said Taolo.

Meanwhile, Botswana will continue to study the occurrence of the bacteria.