Corps refilling Willamette River reservoirs after drawdowns meant to help migrating fish

The Army Corps of Engineers is refilling two Willamette River basin reservoirs that the agency had temporarily drained to historic lows to help fish, but the drawdowns washed mud downstream, threatening drinking water sources.

The deluge of sediment spurred a wave of accusations from Willamette Valley residents and some Republican officials that the corps polluted rivers and possibly killed fish by draining Green Peter and Lookout Point reservoirs so low – achieving the opposite of its intention to help young salmon move down river through the dams. However, the corps and conservationists expect the rivers to run clear again as the agency ends the drawdowns this month, as planned, and begins refilling the reservoirs to protect communities from winter floods. 

Corps officials say it’s too soon to say whether opening the dams and letting the reservoir water drain through achieved the mission of helping young Chinook salmon and steelhead journey to the Pacific Ocean. A federal judge in 2021 ordered the corps to experiment with drawdowns as part of recovery plans for endangered salmon. There is evidence that similar operations at Oregon dams boosted salmon populations. 

At Fall Creek Lake in Lane County, the corps has periodically emptied the reservoir since the 1960s to help fish move downriver, stepping that up to seasonally since 2011. In 2020, 800 natural-born spring Chinook returned to the dam, compared to about 240 in 2007, according to the agency’s data.

“Where it’s been tried, it’s been shown to be extremely effective,” said Kathleen George, an environmental policy expert and member of the Confederated Tribes of Grand Ronde tribal council.

Other drawdowns produced promising results. Jeff Henon, a spokesperson for the corps’ Portland division, said more juvenile salmon survived their journey through Cougar Dam during a drawdown in 2012 and 2013. That’s because the low water level allowed fish to swim through outlets deep within the dam instead of a more dangerous route through hydropower turbines. Federal scientists have been recommending the drawdowns for 15 years.

“These measures have been shown to be effective,” said Margaret Townsend, a senior attorney at the Center for Biological Diversity.

‘Very successful’

The corps’ network of dams in the Willamette River basin protects communities from floods. Most of the dams also produce hydropower, though not much. According to the Bonneville Power Administration, eight dams in the Willamette system produced less than 4% of the total power produced by the federal government’s Columbia River hydro system in 2019. The drawdowns at Green Peter and Lookout Point mean that the dams won’t produce any power for months.

The dams are barriers for migratory salmon that would otherwise swim high in the Cascades to spawn and for their offspring attempting to migrate to the ocean. The corps and wildlife managers have intervened, trapping adult salmon at the bases of dams and trucking them upriver to spawn. But in some cases, after they’re moved upriver of dams they become food for bull trout. 

When reservoir levels are normal, young fish navigate vast lakes that are filled with predators and then spill through the dam when the water level is high enough, or try to go through passages with turbines. 

Research from years of drawdowns at Fall Creek Lake suggests that more fish survive the journey when the reservoir is drained because they can pass through safer outlets in the dam that are otherwise too deep to access. A National Marine Fisheries Service study in 2014 found that 98% of juvenile salmon passed through the dam alive during a deep drawdown, compared to less than 80% when the water level was higher.

The study also found that the drawdown flushed non-native, predatory fish including largemouth bass downriver, which made Fall Creek Lake safer for young Chinook salmon the following year.

“From a biological perspective, this fish passage operation has been very successful,” the corps wrote in 2012.

Like the deluge of mud that flowed from Lookout Point and Green Peter reservoirs, the deep drawdown of Fall Creek Lake sent large amounts of mud down the Willamette River in 2010. The river quickly cleared up, and corps officials say the mud probably didn’t harm young salmon while helping restore the river’s ecology by washing sediment and organisms like plankton downriver.

Operation mired in mud 

Willamette Valley residents have expressed doubt that the operations are benefitting fish because of the thick slurry of mud and old sediment that washed down the Santiam and Willamette rivers when the corps opened dam gates. The deluge sent water managers in Sweet Home, Lebanon and other communities scrambling to filter the sediment from their drinking water.

The Capital Chronicle obtained complaints submitted to the Oregon Department of Environmental Quality that called for investigations of possible water quality violations. Residents asked state officials to intervene.

“Thousands of fish have died. The river has never seen this much turbidity,” one complaint says.

Thousands of kokanee salmon, a type of sockeye salmon that don’t migrate to the ocean, died at Green Peter Dam in October because of the drawdown. However, lower numbers of the fish typically die each year when reservoir levels drop. 

Green Peter Dam is in Republican Rep. Lori Chavez-DeRemer’s 5th Congressional District. The Salem Statesman-Journal reported that Chavez-DeRemer asked U.S. District Judge Marco A. Hernandez for a “better alternative at Green Peter dam to improve fish passage.”

“While I am supportive of efforts to improve salmon and steelhead recovery, this court injunction is causing more harm than good,” she wrote.

Beth Quillian, a spokesperson for the Oregon Department of Fish and Wildlife, said in early December the agency hadn’t received any reports of fish kills since the kokanee die-off. She said the agency supports the drawdowns and that Chinook and steelhead need to pass through the dams.

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By Grant Stringer - Oregon Capital Chronicle