LINCOLN, Neb. (AP) _ Sediment problems have put the Niobrara River on a list of the nation's most endangered waterways.
The American Rivers conservation group announced Wednesday that the nearly 570-mile-long river was 10th on the 2013 list. The Colorado River led the list.
The Niobrara has been on the list three times. Proposed dam projects were cited in listings in 1987 and 1989. The Niobrara was threatened by irrigation diversions in 2008, American Rivers spokeswoman Eileen Fretz said.
``This is the first time that the Niobrara has made the list for sediment,'' Fretz said.
The Niobrara begins in Wyoming and flows through northern Nebraska. It joins the Missouri River near the top of Lewis and Clark Lake, the reservoir formed by Gavins Point Dam near Yankton, S.D.
American Rivers said much of the problem stems from Missouri River sediment that backs up in Lewis and Clark Lake.
The buildup is so extreme at the confluence of the two rivers that the local water table has increased substantially, which American Rivers said can cause flooded farmland and affects boating and other recreation. As the sediment builds within the system, American Rivers said, the lower Niobrara loses the seeps, springs, riparian forests, prairies, and canyons that characterize it as a nationally designated ``wild and scenic river.''
Hydraulic engineer Paul Boyd told the Lincoln Journal Star ( http://bit.ly/11fyTOW ) that the Niobrara contributes a little more than half the sediment deposited near the confluence.
"Certainly, the mouth of the Niobrara is a concern,'' said Boyd, who works for the U.S. Army Corps of Engineers in Omaha. "Over the last 50 years, the riverbed has been coming up due to sediment depositing from the confluence down to Lewis and Clark Lake.
"If we didn't have the Niobrara we would be in a very, very different situation. We wouldn't have as much sand,'' he said.
Various studies have looked at ways to control sediment, and the corps is finishing one that looks at using water from Missouri River dams to flush sediment in the region, Boyd said.