The tailings pond at CNRL's Horizon oilsands project near Fort McKay, Alta. The uncontained western edge of the pond can be seen at the bottom of the picture. (CBC)

A northern Alberta tailings pond appears to have toxic sludge flowing into the muskeg from an uncontained western edge, a situation uncovered by a CBC News investigation.

The pond, located in a remote area about 70 kilometres northwest of Fort McMurray, contains toxic waste from the Horizon oilsands project operated by Calgary-based Canadian Natural Resources Ltd. (CNRL). It has been in operation for about a year.

Mike Orr, a band councillor from the Fort McKay First Nation, is worried about what might happen to the band's traditional food sources if animals drink water from the pond. (CBC)The pond has containing berms on all but its western side. According to documents obtained by CBC News, the company is relying on topography and clay beneath the surface to contain the tailings on that section of the pond.

CNRL is legally permitted to have this setup. The plan was approved six years ago by Alberta's Energy Resources Conservation Board (ERCB).

But members of the Fort McKay First Nation are worried animals they traditionally hunt and trap may be drinking the water flowing from the tailings pond because there isn't a barrier to keep them away.

"I feel like I want to cry," said band councillor Mike Orr. "I grew up on the land. That's the way I was brought up — to live off the land."

Band worries about toxins in food chain

CBC News was invited onto the traditional traplines by members of the Fort McKay First Nation.

Dikes surround the pond on all but the western side.

The land rises slightly at that point and the natural rise in elevation appears to be used to contain the tailings.

University of Alberta water scientist David Schindler watches CBC video of the tailings pond. (CBC)Streams appear to flow toward and away from the tailings pond. Fresh deer and moose tracks are seen going towards the water. Muskrat dams are visible nearby.

The sight upsets Orr, a hunter and trapper who was raised on a trapline. Orr is concerned that toxins in the tailings may get into the food chain.

"They should have a gate or something right around there and no creeks coming to it," he said.

"Divert the creeks or something because we have all that water flowing into here, good clean water with the animals and the beavers ... it's got to stop."

CNRL did not make anyone available for an interview on the weekend, despite several requests for comment from CBC News.

Environment Canada declined comment. A spokesman indicated in an email to CBC News that his department will assess the tailings pond to ensure it complies with federal laws.

Clay not always reliable, expert says

CBC News shot video of the tailings pond and screened it for the world-renowned water expert and ecologist from the University of Alberta, David Schindler.

"This is such a big area," Schindler said as he watched the video. "Some of those chemicals have to be seeping into groundwater and Environment Canada should step in."

Some scientists believe that using the land to contain tailings might be better at keeping toxins out of the water than dikes, which are usually made of sand.

The land beneath the forest floor is made of clay, which is believed to be a natural sealant. But Schindler says clay isn't completely reliable and engineering tests often don't account for holes created by tree roots or burrowing rodents.

"I'd be concerned that there might be some tree root holes that, after the trees die and the roots decay, that there are channels that material could follow either into groundwater or into other surface waters that are lower elevation," he said.

Orr hopes the federal government moves quickly to make sure toxins aren't contaminating the area's food and water.

For his part, Schindler expressed disbelief that regulators would approve this type of tailings pond.

"[I] wonder if the people who approved this have ever gone back for a look," he said.

With files from the CBC's Michael Dick and James Hees