Four conservation groups have made good on their promise to sue the U.S. Army Corps of Engineers for approving the construction of a high-voltage transmission line.

In documents filed last week in federal court, the National Wildlife Refuge Association, Driftless Area Land Conservancy, Wisconsin Wildlife Federation and Defenders of Wildlife groups allege the Army Corps failed to satisfy federal standards before issuing two permits in 2017 and 2018 for the Cardinal-Hickory Creek project.

The $492 million undertaking involves the construction of a 102-mile line from Dubuque County to Dane County, Wis., crossing the Upper Mississippi River National Wildlife and Fish Refuge at Cassville, Wis. The project is a joint venture of ITC Midwest, American Transmission Co. and Dairyland Power Cooperative.

In the lawsuit, the plaintiffs claimed the Army Corps failed to independently assess the environmental impacts of the project, investigate less impactful alternatives and determine whether the project was in the public interest.

They requested the court to overturn the issuance of the permits and prevent the Corps from approving others in the case until an environmental assessment is conducted.

The conservation groups also this year sued the Rural Utilities Service and U.S. Fish and Wildlife Service. Additional litigation against the Wisconsin Public Service Commission is working its way through federal and state courts.