OTTAWA — Canada must limit large-scale industrial activity in its boreal forest, the world's largest intact timberland, to preserve millions of lakes and rivers critical to forming Arctic sea ice, a new report said Wednesday.

Canada must limit large-scale industrial activity in its boreal forest, the world's largest intact timberland, to preserve millions of lakes and rivers critical to forming Arctic sea ice, a new report said Wednesday. The first of its kind study by the Pew Environment Group shows Canada's boreal forest contains more unfrozen freshwater than any other ecosystem, totaling more than 197 million acres of surface freshwater.

"When you look at a color-coded map of the world's (unspoiled) freshwater reserves (marked in blue), it's just shocking to see all the blue in Canada," the study's lead author Jeffrey Wells told AFP.

Canada's boreal forest possesses one quarter of the planet's wetlands, half the world's lakes larger than one square kilometer in size, five of the 50 largest rivers and the single largest remaining unpolluted fresh water body, Great Bear Lake.

Maintaining its flows, which contribute a majority of the freshwater input into the Arctic Ocean, is critical to forming Arctic ice as they decrease the salinity of the sea water, allowing it to freeze more quickly and easily.

But forestry, oil and gas extraction, mining and hydropower generation, the study warned, is rapidly increasing and negatively impacting the boreal water quality and quantity, as well as the surrounding ecosystems.

Lakes have been drained to access minerals underneath or to dispose of tailings and other mine waste. Erosion after logging is increasing amounts of silt and water flowing into rivers, and on a large scale can reduce regional precipitation. Construction of hydroelectric dams also has destroyed or degraded wetlands.

The boreal development footprint is currently 728,000 square kilometers (180 million acres).

Canada has already set aside 185 million acres from development, including key wetland and river areas, representing more than 12 percent of the 1.2 billion-acre forest.

But, the report concludes that governments should protect entire river, lake and wetland ecosystems by preserving intact at least 50 percent of Canada's boreal forest.

It also demands adherence to "sustainable" development in the rest of the vast northern forest.

In eastern Canada, most of the boreal rivers and lakes drain into the immense Hudson and James bays before the water is carried northward to the Labrador Current and flows south into the North Atlantic.

In western Canada, the flow from the Mackenzie River influences the strength and movement of major currents including the Beaufort Gyre and the Transpolar Drift, which carries cold, less-salty polar waters south into the deepwater North Atlantic Conveyor and back to the tropics.

Freshwater from the Yukon River flowing into the Bering Sea similarly contributes to the extensive sea ice of the Bering Sea before continuing north, eventually contributing to the North Pacific Current that rushes through the Bering Strait into the Arctic Ocean.

Stemming these flows would result in less seasonal Arctic sea ice which could hasten the rise in average temperatures worldwide.

Unchecked, warming in turn could lead to decreased precipitation in areas of the boreal forest, drying lakes and ponds that risk becoming so low that they no longer have outflow, the study said.

The Canadian boreal lakes and river delta sediment, peatlands and wetlands are also the largest on-land carbon storehouse in the world, storing more than 400 trillion pounds of carbon, it noted.

The analysis is the first compilation of decades of research on Canadian boreal water reserves from more than 200 peer-reviewed scientific studies, government reports and other sources.