Canadian mining giant Teck Resources says it will appeal a decision forcing it to clean up the Columbia River in Washington.

Teck admitted it discharged toxic slag and effluent from its Trail smelter into the Columbia River for a century, most of which drifted downstream into the U.S.

But the company maintains American authorities can't force it to clean the river.

“This stems from our earliest position on this case: How do two countries deal with issues across the border?” said Teck spokesperson Dave Godlewski.

“Our belief has been nations that share the longest undefended border in the world and have a long history of dealing with issues on a country to country basis should handle this.”

Godlewski also said Teck has spent more than $50 million studying the effects of pollution on the Columbia River and did major reclamation work on a beach just across the American border in Northport Washington.

A judge in Washington found last month Teck intentionally discharged at least 9.97 million tons of slag that included heavy metals such as lead, mercury, zinc and arsenic from 1930 to 1995.

The judge also found Teck knew the hazardous waste disposed of in the Columbia River was likely to cause harm.