The village is about 260 kilometers (161 miles) north of Fort McMurray, the Northern Alberta oil sands hub where a number of projects mine the richest petroleum deposits outside the Middle East, creating toxic pollutants as part of the process that converts the tar-like bitumen stripped from the sand into synthetic crude oil.

Lake Athabasca is fed by the Athabasca River, which also flows past Fort McMurray. While oil sands producers use large amounts of water to produce the crude, contaminated wastes are kept on site and are not released into the river.

The study, released by Fort Chipewyan's Nunee Health Authority, found unsafe levels of arsenic, mercury and polycyclic aromatic hydrocarbon in the lake's fish, as well as in sediments, water and wildlife.

Ecologist Dr. Kevin Timoney analyzed data ranging back to 1970 and claimed levels of the aromatic hydrocarbons have been rising since 2001 to unsafe levels.

More than C$100 billion in new projects are on the books for the oil sands region and production is expected to triple to 3 million barrels a day by 2015, with most of that oil expected to be exported to US refiners.

"There is a need for a moratorium on oil sands development," Russell Kaskamin, a councilor with the Mikasew Cree First Nation, said in a statement. "The federal and provincial governments are continuing to issue approvals for projects despite all the uncertainties with the true environmental effects of oil sands developments."

Last year a doctor in the village reported its population suffered from unusually high rates of rare cancers, thyroid problems and immune-system diseases. His report was contradicted by the Alberta Cancer Board, which found the incidence of cancer to be no higher than the provincial average.

Alberta Health Minister Dave Hancock said the provincial government has only seen a draft of the study but its preliminary view is that the study is based on old data. He cited previous claims about high arsenic levels and the cancers in the area that the government found to be overstated, though he added the province would review the work.

"We take it very seriously," Hancock said. "But we haven't seen the report in its final form or had time to analyze it."