The grim discovery was made over several weeks during an aerial survey.
PIC: The number of African elephants has fallen by around 111,000 to 415,000 in the past decade. (AFP)
Ninety elephant carcasses have been discovered in Botswana with their tusks hacked off, a charity said Tuesday, in what is believed to be one of Africa's worst mass poaching sprees.
Most of the animals killed were large bulls carrying heavy tusks, Elephants Without Borders said.
The grim discovery was made over several weeks during an aerial survey by Elephants Without Borders and Botswana's Department of Wildlife and National Parks.
"We started flying the survey on July 10, and we have counted 90 elephant carcasses since the survey commenced," Mike Chase, the charity director, told AFP.
"Each day we are counting dead elephants," he added.
The animals were shot with heavy calibre rifles at watering spots near a popular wildlife sanctuary in the Okavango Delta.
"The scale of elephant poaching is by far the largest I have seen or read about in Africa to date," Chase said.
The poaching coincided with the disarming earlier this year of Botswana's rangers, according to Chase.
The country has the largest elephant population in Africa at over 135,000.
The number of African elephants has fallen by around 111,000 to 415,000 in the past decade, according to the International Union for Conservation of Nature (IUCN).
The killing continues at a dizzying pace of about 30,000 elephants a year to meet demand for ivory in Asia, where tusks sell for around $1,000 (864 euros) a kilo (2.2 pounds).
Chase said elephants in Zambia and Angola, north of Botswana, "have been poached to the verge of local extinction, and poachers have now turned to Botswana".
Botswana Tourism Minister Tshekedi Khama confirmed to AFP that dozens of elephants had been poached, but gave no further details.
The government was not immediately available to comment on rangers being apparently disarmed earlier this year.
Botswana previously had a zero-tolerance approach to poaching, with a "shoot-to-kill" policy against poachers.
Poachers have also targeted rhino, said Chase, after six white rhino carcasses were found in recent months.