SACRAMENTO – Three environmental groups sued the federal government Monday to block logging along the Salmon River, a major tributary of the northwestern California river that saw one of the nation's largest fish kills in 2002. 

The groups contend the U.S. Forest Service's proposed timber cuts would further endanger salmon populations in the region by raising water temperatures and adding sediment through erosion.

The suit was filed in Sacramento federal court to block logging of 744 acres of old forest along the federally designated wild and scenic river about 55 miles southwest of Yreka near the Klamath Mountains towns of Sawyers Bar, Forks of Salmon, and Cecilville.

The suit alleges the latest proposed logging would add to damage already done by three other recent projects in the Salmon River's watershed. Those timber harvests were the targets of environmental lawsuits and tree-sitters two years ago.

Forest Service spokeswoman Janice Gauthier said she couldn't comment on pending litigation, nor had the service had time to review the suit. But the forest service said in its plan and appeals decisions that the timber sale is aimed at thinning smaller, fire-prone trees to protect larger, fire-resistant trees and open the forest canopy.

The environmental groups contend the service is being deceptive, and the areas marked for logging "are primarily large-diameter old-growth canopy trees and wildlife snags rather than the smaller and intermediate trees."

"Virtually every old growth tree is marked for logging," alleged George Sexton, conservation director of Ashland, Ore.-based Klamath Siskiyou Wildlands Center, one of the nonprofit groups that sued. "They're going after old growth that the Fish and Wildlife Service says is critical to maintaining habitat for an endangered species, the northern spotted owl."

Many of those trees are three to five feet in diameter, he said.

The Klamath Forest Alliance and Environmental Protection Information Center joined in the suit alleging the timber cut violates the Klamath National Forest's management plan and regulations for protecting old-growth trees within the owl's habitat.