Salem, OR.— Marion County is asking a federal judge to block a new U.S. Army Corps of Engineers policy calling for annual deep drawdowns of Detroit Lake, arguing the plan threatens drinking water, fish populations, agriculture, recreation and communities throughout the North Santiam Canyon.
The county filed a motion for a preliminary injunction Monday as part of its federal lawsuit against the Army Corps. The lawsuit was originally filed May 13 in U.S. District Court in Oregon and challenges the agency’s plans under the federal Administrative Procedure Act.
According to Marion County, the Corps’ new policy would lower Detroit Lake below its minimum conservation pool each fall. The reservoir would fall to its lowest historical level during the first year, followed by deeper levels that the county says have not previously been tested in subsequent years.
County officials contend those operations could disturb fine sediment at the bottom of the reservoir, substantially increasing turbidity in water flowing downstream. More than 230,000 people rely on downstream water supplies that the county says could be affected.
The county also argues that a deep drawdown followed by insufficient rainfall could leave the reservoir unable to adequately refill, potentially reducing water available to cities and agriculture. According to the county, the Corps’ own analysis determined that rainfall conditions capable of producing shortages in conjunction with a deep drawdown occur about once every four years.
Marion County points to the 2023 deep drawdown of Green Peter Reservoir as a warning of potential consequences at Detroit Lake.
Green Peter was subjected to a deep drawdown under a federal court order intended to improve downstream fish passage. The operation produced significant turbidity and a major fish kill. Marion County has previously said more than 1 million kokanee salmon died during the operation, with Corps biologists attributing the deaths to barotrauma.
The county’s latest release says the drawdown also damaged downstream water systems and argues similar conditions at Detroit Lake could harm both fish and municipal drinking-water infrastructure.
“Risking the drinking water of our communities while harming thousands of fish is patently absurd,” Marion County Commission Chair Colm Willis said. “Since the Army Corps refused to listen to reasonable requests from the county, cities, and schools, this lawsuit is the strongest means we have to protect our downstream communities as well as recreation at Detroit Lake.”
The Corps has previously said its Detroit Reservoir plan incorporates lessons learned from earlier drawdowns and is designed to reduce effects on downstream communities. In June, the agency said it understood communities’ dependence on clean drinking water and that its approach at Detroit had been modified based on those lessons.
The dispute stems from federal efforts to improve conditions for threatened Upper Willamette River spring Chinook salmon and winter steelhead. Deep reservoir drawdowns are intended in part to improve downstream passage for juvenile fish, but local governments contend the potential consequences for drinking water and other resources have not been adequately addressed.
Marion County’s lawsuit initially sought to stop the Corps from proceeding until it completed a turbidity report required by Congress and provided an opportunity for public review. Several Santiam Canyon communities have also opposed the planned drawdown, while the City of Salem filed a separate lawsuit in July seeking to pause the operation.
Commissioner Kevin Cameron said the county considers the potential drinking-water consequences unacceptable.
“Our residents depend on clean, reliable drinking water,” Cameron said. “The Army Corps should not be gambling with the safety of drinking water in our community.”
Commissioner Danielle Bethell said the county would continue challenging the policy because officials believe adequate safeguards have not been established.
“Water management must be grounded in data-backed science with meaningful protections in place for our communities,” Bethell said.
The requested preliminary injunction would allow a federal judge to determine whether the Corps can proceed with the planned drawdown while Marion County’s broader lawsuit remains pending.
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