They're concerned about gray wolf, Canada lynx habitat.

Two environmental groups are suing to block a land exchange for the planned PolyMet copper-nickel mine in northeastern Minnesota, saying the project would destroy important habitat for the gray wolf and Canada lynx.

The Center for Biological Diversity and Earthworks on Tuesday filed the legally required 60-day notice of intent to sue the U.S. Fish and Wildlife Service and the U.S. Forest Service for agreeing to the land swap. They say the mine would destroy nearly 4,000 acres of habitat for wolves and lynx, which are listed as threatened.

The Forest Service on Monday approved trading 6,650 acres of the Superior National Forest to PolyMet for about the same amount of private land elsewhere in the forest. The Fish and Wildlife Service says the mine won't significantly harm either species.