Environmentalists on Tuesday sued in federal court to block the Highway 101 Willits bypass, which was on the verge of construction after more than five decades of planning and debate.

"We will be seeking an injunction" to stop the project from moving forward, said Jeff Miller of the Center for Biological Diversity, an Arizona-based organization with its nearest office in San Francisco.

Caltrans officials said they had not had a chance to evaluate the lawsuit, but "if they ( were to get an injunction, that could potentially delay the project," said spokesman Phil Frisbie. Caltrans had planned to begin seeking bids on the $210 million, 5.9-mile project this month. The bypass would skirt Willits to the east and eliminate the only stop light on Highway 101 between San Francisco and Eureka.

The lawsuit was filed in San Francisco federal district court by four environmental groups, including Miller's organization, the Willits Environmental Center, the Redwood Chapter of the Sierra Club and the Environmental Protection Information Center.

It targets Caltrans, Caltrans acting Director Malcolm Dougherty, the Federal Highway Administration and the U.S. Army Corps of Engineers, alleging they violated the National Environmental Policy Act and Clean Water Act in approving the project.

The groups contend the Willits bypass is unnecessary and will harm wetlands, salmon-bearing streams and endangered plants.

"Bulldozing a freeway the size of Interstate 5 through precious wetlands would be wasteful and destructive," Miller said.

While the project had been whittled by lack of funding from four lanes to two, it would entail grading for four, he said. Caltrans hopes to widen the bypass when, or if, additional funding materializes.

The project would result in the loss of nearly 100 acres of wetlands, Miller said. "It's the largest wetlands fill in northern California in nearly 50 years. It might even be the largest," he said.

The project also would impact Outlet Creek, which has tributaries that support salmon and steelhead, he said.

Caltrans purchased land to compensate for the loss, but it's inadequate, he said.

Ellen Drell of the Willits Environmental Center said the project is unnecessary. Caltrans should be improving public transit and maintaining existing roads rather than "clinging to outdated visions of new freeways," she said.

You can reach Staff Writer Glenda Anderson at 462-6473 or Glenda.anderson@pressdemocrat.com.