Anthrax is believed to have killed 128 bison northwest of Fort Providence, N.W.T.
The carcasses were found close to Mills Lake during a routine anthrax surveillance flight this week.
The Department of Environment and Natural Resources has issued an anthrax emergency response plan to deal with the potential outbreak.
"A field test on a couple of carcasses did turn out positive," said Judy McLinton, the department’s spokeswoman. "Given the number of carcasses and the chance when they looked at them that it was probably or potentially anthrax, we activated our emergency response plan."
On Thursday, the department sent samples from the dead animals to a Canadian Food Inspection Agency lab in Lethbridge, Alta. for testing, she said. They expect the results in a week’s time.
McLinton said the department will start disposing of the carcasses. Typically they burn carcasses that have died of anthrax but given the number, she said that could take up to six weeks.
"They’ll treat the carcasses with formaldehyde, tarp them, because we want to keep the anthrax spores intact, and then we’ll burn as we move along."
McLinton said it’s not possible to vaccinate bison for anthrax because the spores are in the soil.
She said the wet weather followed by a hot, dry stretch, contributed to the outbreak.
"What happens is if you get the right environmental conditions, which we have right now, in that area, the spores are in the ground, the bison go in, start rolling around, wallowing in the mud near the water and the spores come up and [the bison] inhale it," she said.
McLinton said the last large outbreak in the Mackenzie Bison Sanctuary was in 1993 when 172 animals died. She said anthrax killed nine bison in the Mills Lake area in 2009.
People with cabins in the area have been warned to stay away from the dead bison and the department said anyone who sees bison carcasses should call ENR right away.