Federal officials are releasing a plan to recover struggling bull trout populations in five Western states with the goal of lifting Endangered Species Act protections.

The U.S. Fish and Wildlife Service says the draft plan for six recovery units spread over Idaho, western Montana, Washington, Oregon and a tiny portion of northern Nevada will be released on Thursday with public comments being taken through July 20.

The agency proposes allowing the lifting of federal protections in the six recovery units individually when specific requirement are met. The agency said the recovery units contain distinct populations of bull trout with unique characteristics.

"We think the approach is tactical and appropriate," said Steve Duke, bull trout recovery planning coordinator for the agency. "We think it focuses on what still needs to be done, and it lets local agencies and those with managerial oversight focus on those areas without having to look at the larger distribution of bull trout."

Specifically, the agency identifies 111 core bull trout areas in the six recovery units. Duke said the plan doesn't dictate actions, but looks at ways to keep clean and cold water in streams.

The draft plan is the result of a settlement the agency made last year following a lawsuit by two environmental groups — the Alliance for the Wild Rockies and Friends of the Wild Swan.

Michael Garrity of Alliance for the Wild Rockies said he's concerned the agency is looking to define bull trout differently in different regions so federal protections could be removed in some areas while fish are still in trouble in other areas. He said his organization would be against that plan.

"We're optimistic they'll listen to us," Garrity said. "But we're optimistic because we've sued them on bull trout about a dozen times and won each time. If they don't follow the best available science, we won't hesitate to sue again."

Bull trout are a cold water species listed as threatened in the lower 48 in 1999. Both Garrity and Duke said maintaining cold and clean water is essential for bull trout.

Non-native brook trout are a problem because they can hybridize with bull trout. Other problems include isolated of populations. The plan also considers warming waters due to climate change that is forcing some populations, Duke said, into upper regions of river systems.

"We expect that to continue into the future," he said.

He said the presence of bull trout is often a sign of a healthy river system.

"They're a good indicator species for a variety of reason," Duke said.

He said that bull trout occupy about 60 percent of their former range, which he noted has remained steady since the fish received federal protection in 1999.