"It's not a huge amount," Eriel Deranger, spokeswoman for the Athabasca Chipewyan First Nation, said Tuesday. "But there is obviously a petrochemical of some kind in the Athabasca River system in such great quantities from upstream that it is now residing on the shores of Lake Athabasca."
Reports of dead fish are also coming in.
"There are numerous reports of dead fish being found along the delta, within the lake and the river system," Deranger said.
"None of the land users have ever heard of or seen anything like this on the Athabasca."
The sheen was first spotted late Friday night, said Deranger.
"A member of the (First Nation) was boating from Fort McMurray to Fort Chipewyan and just before he reached Poplar Point reserve, he started noticing that there was oil residue on the water," she said.
"It wasn't just a small area. The sheen was shoreline to shoreline."
Crews from the First Nation responded Saturday morning. The provincial government and Alberta's energy regulator were also notified.
As a precaution, the community's water intake on Lake Athabasca was shut down. It was still closed Tuesday.
Athabasca Chipewyan Chief Allan Adam and others from the band went up in a helicopter to survey the river.
"He and the folks on the ground realized that the sheen was much larger than five kilometres," Deranger said. "It wasn't shore to shore in all places but the sheen extended more than 100 kilometres."
Teams from Alberta Environment also took to the skies on Saturday and couldn't see anything, said spokeswoman Jessica Potter.
"It landed a couple of times where they saw some darkening, but it was determined to be silt. They couldn't see a sheen."
A sheen was clearly visible in photographs taken by band members Saturday.
Water samples taken by both the government and band are being analyzed. Band officials were also collecting samples and photographs of dead fish.
The government was sending a boat to the stretch of affected river Tuesday to take a closer look. Crews were to examine rocks and beaches along the river and also the location where it flows into Lake Athabasca.
Energy companies in the area say they haven't experienced any spills or releases.
Potter said one possible explanation is that heavy rains recently caused an unusual amount of erosion along the banks of the river, which cuts through natural bitumen deposits. High temperatures that followed may have softened the freshly exposed bitumen and allowed more than the usual amount to seep into the waterway.
Deranger said chemical analysis should be able to tell fairly readily whether the substance is natural bitumen or a refined petrochemical.
Either way, she said, the people of Fort Chipewyan have health concerns.
"Even if this is natural, it poses a serious health risk. The fact that the government has completely failed to do anything to remediate or clean up this film shows their lack of concern."
Potter said new, more intensive environmental monitoring on the Athabasca should eventually help in such situations.
"These are the things we're looking to differentiate — what's the background and what's new. That is the goal of the joint oilsands monitoring program, to really get an actual understanding of the full scope of what's going on, rather than just compliance monitoring."
— By Bob Weber in Edmonton
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