Chile's glaciers are on the retreat, a sign of global warming but also a threat to fresh water reserves at the southern end of South America, a report has found.

In a November report, the Chilean water utility -- Direccion General de Aguas de Chile (DGA) -- said the Echaurren ice fields, which supply the capital with 70 percent of its water needs, are receding up to 12 meters (39.37 feet) per year.

Twenty of the glaciers studied receded between 1986 and 2007 in Campos de Hielo Sur, the third largest ice reserve in the world after Antarctica and Greenland. At the current rate of decline, Echaurren and other small glaciers close to Santiago could vanish over the next half century.

"The results indicate that the Campos de Hielo Sur glaciers generally tend to recede, which could be due to climate change in the region," the study said.

"The glaciers have receded up to 580 meters (1,900 feet) due to reduced rainfall recorded by weather stations in Patagonia and temperatures rising by about one degree Celsius (1.8 degrees Fahrenheit) in the region over the last century."

The Chilean glaciers, located mostly in the remote flatlands of Patagonia, have receded by about 67 meters per year between 1986 and 2001 and by about 45 meters between 2001 and 2007, according to DGA.

The Jorge Montt receded the most of all glaciers studied, by 11 kilometers (6.8 miles) in 21 years, a loss of 40 square kilometers (25 square miles). The San Rafael glacier in southern Chile lost 12 kilometers (7.45 miles) over 136 years.

"The fact that the glaciers are receding is one of the most dramatic consequences of global warming, because that's where climate change is most obvious," glaciologist Andres Rivera of the Valdivia scientific studies institute (CECS) told AFP.

The melting or collapse of the ice wall formed at a glacier's extremity is not due solely to global warming, according to the scientists who wrote the DGA study. The depth of the lakes or fjords into which they fall also causes the glaciers to crumble.

Loss of glaciers along Chile's Andes mountain range, home to 76 percent of South America's glaciers over a surface of 20,000 square kilometers (12,400 square miles), is threatening the water supply for people and agriculture.

"The glaciers will continue to provide fresh water for at least a hundred years. The cities and crops will expand and a time will come where the glaciers will be the population's water source," the study warned.

But two glaciers bucked the trend. Pie XI, the biggest glacier in Hielo Sur, is also the only one that continues to expand in Chile. Perito Moreno in neighboring Argentina is its only glacier that is still spreading.

"These two examples are anomalies, exceptions in this region where the glaciers are receding and losing mass."