When the Okavango River, a dark green ribbon cutting through the Angolan Highlands, reaches the Kalahari Desert in Botswana it branches into the lush Okavango Delta.

A UNESCO World Heritage site, the delta covers about 5,791 square miles in northern Botswana. The oasis is home to more than 2,000 species of animals and plant life, including elephants, rhinoceroses and the endangered African wild dog. Described as “Africa’s last Eden,” it draws thousands of visitors every year.

But recently, conservationists came across a disturbing discovery near the famed wildlife sanctuary: the bodies of 87 elephants, many of which bore brutal injuries consistent with being killed for their tusks.

“I’m shocked, I’m completely astounded,” Mike Chase, founder of the conservation group Elephants Without Borders, told the BBC. “The scale of elephant poaching is by far the largest I’ve seen or read about anywhere in Africa to date.”

On Tuesday, the Botswana government issued a statement disputing the group’s claims, calling the statistics “false and misleading.” According to the statement, Elephants Without Borders only reported seeing 53 elephant carcasses while conducting aerial wildlife surveys supported by the government between July and August. An additional “verification mission … established that the majority were not poached but rather died from natural causes and retaliatory killings as a result of human and wildlife conflicts,” the statement said.

Chase said that each of the 87 dead elephants has a GPS location and every survey flight had four people aboard the plane, including a government employee. Voice recordings were also taken during the flights, Chase said. “I am an objective scientist, with no political agenda,” he said. “I am sad that our government has responded in this way.”

Botswana is home to one of the largest elephant populations in Africa, more than 130,000, according to the Great Elephant Census, which is considered the largest wildlife survey in history. The census found about 350,000 elephants in 18 African countries.

In a tweet Monday, Elephants Without Borders described the recent rate of poaching as “alarming.”

“When I compare this to figures and data from the Great Elephant Census, which I conducted in 2015, we are recording double the number of fresh poached elephants than anywhere else in Africa,” Chase told BBC.

An elephant carcass is described as “fresh” when it is killed within the last three months, but a majority of the elephants found near the delta died in recent weeks, NPR reported, citing an Elephant Poaching Incident Report Reference written by Chase.

According to the report, all the carcasses were “presumed to be poached” because “all of them had their skulls chopped to remove their tusks.” The wide range of classification and age of the dead elephants indicated a “poaching frenzy” that “has been ongoing in the same area for a long time.”

Poachers had attempted to conceal the “mounds of rotting flesh” with drying bushes, the report said.

In addition to the elephants, five white rhinoceroses had also been poached from the area in recent months, the BBC reported.

About four months ago, the government made a controversial decision to disarm Botswana’s anti-poaching unit, just one month after President Mokgweetsi Masisi was sworn into office. It’s a move that goes against Botswana’s former policy against poachers, which had garnered praise from conservationists for its “shoot to kill” stance.

“People did warn us of an impending poaching problem, and we thought we were prepared for it,” Chase told the BBC. “The poachers are now turning their guns to Botswana. We have the world’s largest elephant population and it’s open season for poachers.”

In its statement, officials also pushed back against the notion that taking weapons away from the Department of Wildlife and National Parks’s (DWNP) anti-poaching unit has contributed to the rise in poaching.

Since the 1980s, the country has instructed all its security agencies to take part in the anti-poaching effort, a practice that is still ongoing, the statement said.

The recent decision, the government said, “has not created any vacuum in anti-poaching operations as the anti-poaching unit in DWNP continues to play a pivotal role in combating wildlife crime through other strategic interventions.”

Given the country’s harsh anti-poaching policies, Botswana has long been known as a place where wildlife can thrive, largely free from human threats.