A new report from the World Wide Fund for Nature predicts devastating declines in wildlife populations over the next five years, unless quick action is taken.

By the end of the decade, we’re likely to have lost 67 percent of all vertebrate wildlife compared to 1970, it says.

According to this year’s Living Planet Report, released every two years, wildlife populations have already suffered tremendous losses in the last few decades. Vertebrate populations have plunged by 58 percent overall since 1970, the report says. And organisms living in freshwater systems, such as rivers and lakes, have fared even worse, declining by 81 percent in the last four decades.

“For decades scientists have been warning that human actions are pushing life on our shared planet toward a sixth mass extinction,” wrote Marco Lambertini, director general of WWF International. “Evidence in this year’s Living Planet Report supports this.”

The biennial report relies on data from the Living Planet Index , an ongoing project that monitors changes in more than 18,000 wildlife populations composed of nearly 4,000 animal species.