Temperature and other water quality changes in the lower river have affected aquatic insects like salmon flies, although it's not clear if those changes are causing bug populations to decline. Amanda Peacher / OPB

A central Oregon conservation group has filed a lawsuit against Portland General Electric over water quality on the lower Deschutes River.

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The Deschutes River Alliance says PGE has violated water quality standards for several years after installing a water-mixing device at Round Butte Dam, one of three dams along the lower Deschutes River.

The giant device, also called a “selective water withdrawal tower,” pulls warm water from the reservoir’s surface to blend with cold water from the bottom. The mix is intended to more closely resemble conditions were the dam not in place.

Related: Conservationists Sue PGE Over Water Quality Standards At Round Butte Dam

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The discharge that ultimately emerges from the dam is a warmer blend from the three tributaries of the lower Deschutes — the Crooked, the Metolius and the Middle Deschutes rivers.

But DRA president Greg McMillan said PGE has failed to meet water quality certification standards at the site hundreds of times since the mixing device was installed in 2009.

"We’ve logged and documented 1,600 violations of the water quality requirements. All of these standards are set to protect the life in the river, as opposed to being arbitrary numbers," said McMillan.

PGE and the Warm Springs Tribes agreed in 2009 to spend about $110 million to install a water mixing tower in the reservoir.

In an earlier interview with OPB, Oregon's Department of Environmental quality said the Deschutes River Alliance exaggerates the water quality violations below the dams. State regulators said that the water quality requirements have some built-in flexibility, given that the water mixing tower is relatively new and is the only facility of its kind in the nation.

PGE has indicated it will challenge the suit. The utility says it works closely with state water quality regulators.

"However, we recognize that this is a long-term project with long-term goals," PGE officials said in a statement Tuesday. "Restoring an ecosystem that was fundamentally changed 50 years ago will take significant time and investment."