About 125,000 western lowland gorillas have been found living in a swamp in equatorial Africa.
“It’s pretty astonishing,” Hugo Rainey, one of the researchers who conducted the survey for the U.S.-based Wildlife Conservation Society, told CNN Tuesday.

The last census on the species, carried out during the 1980s, estimated that there were only 100,000 of the gorillas left worldwide. Since then, the researchers estimated, the numbers had been cut in half.

WCS survey teams conducted the research in 2006 and 2007, traveling to the remote Lac Tele Community Reserve in northern Republic of Congo, a vast area of swamp forest.

Acting on a tip from hunters who indicated the presence of gorillas, Rainey said that the researchers trekked on foot through mud for three days to the outskirts of Lac Tele, about 80 kilometers (50 miles) from the nearest road.
Western lowland gorillas are listed as critically endangered, the highest threat category for a species. Their populations are declining rapidly because of hunting and diseases like Ebola hemorrhagic fever, whose symptoms include diarrhea, vomiting and internal and external bleeding.

War, habitat loss, poaching and disease are the major threats to the mountain gorillas, made famous by researcher Dian Fossey and the film “Gorillas in the Mist.” The mountain gorilla population is starting to recover after decades of conservation work. From a population of around 230 in the 1970s, the mountain gorillas now number around 700, the WCS says.