Pennwest Exploration says between 400,000 and 600,000 litres of salty waste water escaped from the pipeline in addition to 5,000 litres of oil initially reported.
"Groundwater, and also the environmental damage for wildlife ... that's always the concern," said Billy Joe Laboucan, chief of the Lubicon Lake Cree.
"Especially if it's in a boggy area. It's really hard to get all of that. It seems to seep it."
Alberta Environment said Monday that a swampy area of muskeg and wetlands just under two hectares in size has been affected.
Pennwest has said no waterways have been touched.
Nobody from the company was available Monday. Pennwest's headquarters are in downtown Calgary, which remained largely deserted due to heavy flooding.
The spill is about 20 kilometres from the aboriginal community of Little Buffalo. It is regularly used by locals for hunting and trapping.
Laboucan said effects are still visible from a 2011 leak from a Plains Midstream pipeline, which released 4.5 million litres of oil into similar terrain.
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