BOISE, Idaho - An Idaho Indian tribe working to save a dwindling population of endangered white sturgeon is seeking to intervene in a lawsuit so it can challenge an environmental group's plan to help the largest freshwater fish in North America from becoming extinct.

The Kootenai Tribe has asked a federal judge in Montana to allow it to join a lawsuit over the operation of Libby Dam, which controls the flow of the Kootenai River from Montana, across the Idaho Panhandle to Corra Lin Dam at the end of British Columbia's Kootenay Lake.

The 167-mile stretch is the only place along the river where the fish - which can grow as long as 19 feet and live for a century - can be found. Since the dam was completed in 1974, the fish have never successfully reproduced in the river and an estimated 500 wild sturgeon remain, a number expected to drop to 50 by 2030.

White sturgeon are found in large rivers between Ensenada, Mexico, and Cook Inlet, Alaska, including the Columbia and Sacramento rivers, where their numbers also have been in severe decline.

In May, the Center for Biological Diversity filed the latest in a series of lawsuits against the federal government, alleging the plan for the sturgeon's recovery in the Kootenai does not require enough water to be sent through Libby Dam to improve the sturgeon's chances of reproducing and reverse its steady decline.

The suit in U.S. District Court in Missoula, Mont., challenges the latest "biological opinion" on the sturgeon from the U.S. Fish and Wildlife Service and seeks to force installation of additional turbines at Libby Dam to accommodate higher releases of water.

Center for Biological Diversity biologist Noah Greenwald of Portland, Ore., said during a high-water period last month, white sturgeon were seen in areas of the river favorable to spawning that they normally don't visit because the water levels are not high enough.

But Kootenai Tribal leaders and Idaho local government officials downstream say higher flows in the Kootenai will cause extensive flooding in the town of Bonners Ferry and riverside homes and farms. In mid-June, Libby Dam operators had to dump water over spillways to prevent the Koocanusa Reservoir from overflowing due to snowmelt and heavy rainfall.

The record June discharge sent the Kootenai to 3 feet above flood stage at Bonners Ferry, the highest it has been since the dam was built. Idaho authorities say the flooding caused more than $50 million in damage to farm fields, dikes and riverfront property. Hundreds of volunteers piled sandbags around the Kootenai tribe's riverside casino and hotel to protect it from the advancing river.

Kootenai Tribal Attorney Billy Barquin said although the tribe does have fears of flood damage to property and cultural artifacts, its primary interest is saving the sturgeon. The tribe supports the latest Fish and Wildlife Service biological opinion, contending its flexible "adaptive management" approach allows for experimentation with river channel reconstruction and creation of spawning habitat that may make additional flows from Libby Dam unnecessary.

"While we don't agree with everything the feds are saying, we think the habitat modifications are going to work best and we can get those implemented without as much damage as the high flows," said Barquin. "Throwing this biological opinion out and making us do a new one is not what the species needs."

U.S. District Judge Donald Molloy has yet to rule on whether the tribe can join the lawsuit. The state of Montana, which also opposes spilling additional water from Libby Dam, has also intervened in the case.

On the Net:

Sturgeon Recovery: http://www.fws.gov/endangered/features/sturgeon/

Center for Biological Diversity: http://www.biologicaldiversity.org/swcbd/