The Klamath Tribes of southern Oregon are suing federal water managers over low water levels in Upper Klamath Lake, which the suit alleges put two endangered species of fish at risk of extinction.

The suit, filed Thursday in federal court, names the Bureau of Reclamation, which manages water in the Klamath Basin, along with the U.S. Fish and Wildlife Service and the National Marine Fisheries Service.

The lost river and shortnose suckers, known as C'waam and Koptu, respectively, to the tribes, were listed under the Endangered Species Act in 1988. The fish are important to the tribes for subsistence and as a vital part of their culture.

"Our creation story tells us that if the C'waam go away, the people go away," Don Gentry, tribal chairman, said in a statement. "The science makes it clear that this was the only option left to us to address the water and fish emergency in the lake."

The species have steadily declined as lake levels have dropped and water quality has eroded, said Mark Buettner, a fisheries biologist for the tribes.

Specific lake levels were mandated in a 2013 federal document called a biological opinion, but the tribes say those levels are now insufficient for the survival of the species and need to be retooled.

"These fish are reaching a tipping point. Too many fish are dying before they're old enough to reproduce," Buettner said in a statement. "Most of the younger fish are offspring of older fish that are nearing the end of their lifespans. We're basically looking at a biological bottleneck."

The tribes have voluntarily suspended fishing and now harvest only two fish per year for tribal ceremonies.

The suit calls upon water managers to take "immediate, emergency measures" to provide adequate water levels for the species' survival.

A spokeswoman for the Bureau of Reclamation said the agency works with the tribes regularly and will continue to do so, but declined to comment on pending litigation.

-- Kale Williams

kwilliams@oregonian.com

503-294-4048