Ernest Tonka, a member of the Liidlii Kue First Nation, told leaders gathered at the Deh Cho assembly in Kakisa last week that the Colomac mine near Yellowknife was one of the worst environmental disasters he has ever seen.
Tonka said he worked at the mine before it closed.
"I'm telling you the truth, they don't care about the land," he said of mining companies.
Expanding Nahanni National Park's boundaries and attempting to protect the Nahanni watershed may be futile unless Canadian Zinc Corporation's Prairie Creek mine is cleaned up, said Marie Lafferty, president of the Fort Simpson Metis Nation.
If the stockpile of cyanide stored at the site spills into the river system, the population of the Mackenzie Valley, "is going to be gone," Lafferty warned.
The park's superintendent, Chuck Blyth, said the Deh Cho's other mine -- North American Tungsten's CanTung site -- will be extremely costly to clean up.
The mine was expected to emerge from bankruptcy protection last week.