Gov. Brian Schweitzer said Tuesday that Stimson Lumber Co. needs to clean up contamination at the company’s mill site in Bonner now that the mill is closed.

The company countered that it has planned to clean up the location.

Stimson recently closed the plant after 122 years of logging operations, citing a deteriorating housing market and falling timber prices.

The governor said Tuesday that pollution in a holding pond could get into the Blackfoot and Clark Fork rivers.

Schweitzer said that the Montana Department of Environmental Quality has found the pond is contaminated with PCBs and other toxic compounds. Cleanup would cost $5 million.

A failure of the pond when the river is running high could release pollution, he said.

‘‘This is a very important site,’’ Schweitzer said. ‘‘It sits immediately upstream from the Milltown Dam site, one of the most outstanding examples of Montana’s efforts to establish our restoration economy.’’

Stimson said it was surprised by Schweitzer’s announcement.

But the company said it already has hired an environmental firm to evaluate the site, and is waiting for the recommendations the come from the review.

‘‘It has always been our intent to make this site attractive to another industrial user who will bring jobs back into the community,’’ Jeff Webber, Stimson vice president, said in a release. ‘‘Stimson Lumber Company is fully committed to environmental cleanup of the Bonner mill site.’’