A dead elephant is seen in this undated handout image in Okavango Delta, Botswana May-June, 2020. The number of elephants found dead in Botswana's Okavango Panhandle has risen to 275 from 154 reported two weeks ago, the government said on Thursday. PHOTOGRAPHS OBTAINED BY REUTERS/Handout via REUTERS

A dead elephant is seen in this undated handout image in Okavango Delta, Botswana May-June, 2020. Authorities are investigating the unexplained deaths over the past months. Poaching has been ruled out as the carcasses were found intact. PHOTOGRAPHS OBTAINED BY REUTERS/Handout via REUTERS

A dead elephant is seen in this undated handout image in Okavango Delta, Botswana May-June, 2020. In the report, EWB put the death toll at 356 and Chase said urgent action was needed to establish if the deaths were caused by disease or poisoning. PHOTOGRAPHS OBTAINED BY REUTERS/Handout via REUTERS

A dead elephant is seen in this undated handout image in Okavango Delta, Botswana May-June, 2020. Africa's overall elephant population is declining due to poaching but Botswana, home to almost a third of the continent's elephants. PHOTOGRAPHS OBTAINED BY REUTERS/Handout via REUTERS

A dead elephant is seen in this undated handout image in Okavango Delta, Botswana May-June, 2020. PHOTOGRAPHS OBTAINED BY REUTERS/Handout via REUTERS

A dead elephant is seen in this undated handout image in Okavango Delta, Botswana May-June, 2020. PHOTOGRAPHS OBTAINED BY REUTERS/Handout via REUTERS