The waste water that leaked from a failed berm at the Obed Mountain Coal mine near Hinton, Alta. is now near Fort McMurray and moving north.

Aboriginal communities near Lake Athabasca in Alberta say they're worried about the long-term effects of the spill, and experts agree.

The contaminated sediment is expected to go through Fort Chipewyan any day now and to reach Lake Athabasca between Nov. 29 and Dec. 3.

At least one expert says some of the chemicals will likely stay there.

Donna Lisenby

Donna Lisenby works with the U.S.-based Waterkeepers Alliance, in concert with the Keepers of the Athabasca. (Waterkeepers Alliance)

Donna Lisenby is a scientist with the Waterkeeper’s Alliance in North Carolina with 16 years experience in water sampling and investigating the coal industry there.

“Heavy metals are exactly what they sound like: they're heavy, they sink,” Lisenby says. “Coal waste contaminants sink to the bottom of the river and when big floods happen... they move further downstream.”

Lisenby says the further downstream the plume travels, the less toxicity you'll see in the water. "Where you see it is in the sediment," she says. She says the sediments could takes years to arrive, but they will eventually migrate downstream. She says that sediment could affect the food that fish eat. 

"The tragedy here is that it's already in the river. We really don't know how long or how far it will go." 

Lisenby says the longer the clean-up is delayed, the harder it will be. She also says local water monitoring is key. 

Bruce Maclean manages a community based monitoring program for the Athabasca Chipewyan First Nation. He worries the sediment would blanket fish habitat in Lake Athabasca with contaminants.

“That sediment contains most of the contaminant load and so that will remain in the delta," Maclean says, "and will impact literally everything that relies on the sediment.”