Deforestation, pollution, overfishing and the illegal wildlife trade, together with climate change, "are pushing species populations to the edge," according to the Living Planet report released Thursday by WWF and the Zoological Society of London.
The assessment predicts that by 2020, populations of vertebrate species could have fallen by 67 percent from 1970 levels unless action is taken to reverse the damaging impacts of human activity.
One of the actions pushing the decline is the growing number of humans, which is driving overfishing, hunting and the destruction of habitats. The report detailed the strain that agriculture places on freshwater systems.
"Human behavior continues to drive the decline of wildlife populations globally, with particular impact on freshwater habitats," said Ken Norris, director of science at ZSL. "Importantly, however, these are declines - they are not yet extinctions - and this should be a wake-up call to marshal efforts to promote the recovery of these populations."