A national environmental group says operation of Flaming Gorge Dam in Utah should be changed greatly to help protect endangered fish in the Green and Colorado rivers.

The Environmental Defense Fund says the dam should reduce current fluctuations in water discharges and try more to mimic historical flows that occurred before the dam was built.Of course, that would decrease the amount of peak-time electrical power the dam could produce - which could increase power rates for cities that buy it. It could also affect seasonal downstream water supplies.

The government plans similar changes at Glen Canyon Dam - but that is to protect the Grand Canyon. The fish that would be protected by changes at Flaming Gorge are considered "trash" fish by critics.

The recommendation came Monday as the defense fund released a study saying endangered species in rivers and lakes are much more imperiled than land mammals and birds. It said a third of North American fish are threatened, endangered or imperiled, but only 13 percent of mammals and 11 percent of birds are.

The report, "The Big Kill," included 10 case studies on what could be done in some areas to better help endangered fish - including in the Green and Colorado rivers to help the Colorado squawfish, humpback chub, bonytail chub and razorback sucker.

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It said studies say current operation of Flaming Gorge dam interferes with the mating and migration of those species by changing historical flow patterns.

For example, it said, "Abrupt fluctuations in surface water elevation from late summer to spring are believed to strand squawfish and other backwater species."

It said unnaturally high summer and early autumn flows allowed by reservoir operations also scatter squawfish and make it more difficult for them to mate.

The group said, "Flaming Gorge is the key to rehabilitation of the Green as a habitat for these fish. Operating as a peaking power facility, it's the greatest threat to recovery in this basin."

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