The Pantanal, a stunning biodiversity sanctuary in central-western Brazil, is threatened by intensive farming and deforestation, a leading environmental group warned as the world marked World Wetlands Day on Thursday.

Often referred to as the worlds largest freshwater wetland system, the Pantanal extends through millions of hectares of Brazil, eastern Bolivia and eastern Paraguay.

It includes sanctuaries for migratory birds, nursery grounds for aquatic life, and refuges for such creatures as the yacare caiman, deer, and jaguar. Some 4,500 different species live in the Pantanal.

A leading environmental group, the World Wildlife Fund for Nature (WWF), is sounding the alarm about the growing threat to the region posed by intensive farming, deforestation, urban growth and the proliferation of hydro-electric dams.

As evidence the group cites a three-year study by 30 experts from Brazil, Paraguay, Bolivia and Argentina, the counties that share the Paraguay river, which flows from its headwaters in Mato Grosso about 2,600 kilometers (1,620 miles) to its confluence with the Parana River in Argentina.

"The Pantanal is under threat," said biologist Glauco Kimura, who coordinates the Water for Life program at WWF.

"This may seem surprising but it is the sad reality. Our study shows that 14 percent of the Paraguay River basin must be urgently protected," Kimura said.

Navigating the Cuiaba river, an important Pantanal tributary, escorted by raptors and colorful parrots overhead, Kimura and his team stop at the Chapada dos Guimaraes National Park, on a plateau at the edge of the Pantanal.

The threat, Kimura explains, comes from the highlands, known here as the Planalto.

"This region is like a plate," explains Kimura. "The Planalto on the edges and the Pantanal at the bottom of the plate." The Pantanal suffers from what goes on in the highlands, he says.

There are thousands of acres of farmland across the highlands. Soybeans are the regions biggest crop, but corn, rice, cotton and sugarcane are also planted.

The Pantanal is also at risk from deforestation as cattle farmers cut down trees to make room for land for grazing.

Roughly 15 percent of the region's native vegetation has already been destroyed to make way for soybean cultivation and cattle ranching, according to the WWF, resulting in soil degradadation.

This worries Pierre Girard, a Canadian hydrologist at the Pantanal research center.

"Soybean is cultivated at the headwaters of the rivers that feed and then form the Pantanal. There are risks of erosion, but also of contamination of the Pantanal," he warns.

The WWF study -- conducted jointly with the US-based Nature Conservancy, another leading environmental group -- underscores the need for joint action by the countries and regions affected.

"There is no more space for intensive farming as if there was an infinite stock of native forest to destroy and fresh water to pollute," says Kimura. "We need to protect ground water, create more protected areas and improve agribusiness practices."

Kimura believes that protecting the Paraguay river basin is crucial to conserve the region's unparalleled wildlife diversity. Currently only 11 percent of the basin is protected.