Salem and Marion County go to federal court Tuesday, Oct. 6, to block the Army Corps of Engineers from draining Detroit Lake this fall.

The stakes: drinking water for roughly 220,000 people who depend on the reservoir, including Salem residents, hospitals, schools, the City of Turner and emergency supplies for Stayton and Keizer.

U.S. District Judge Mustafa T. Kasubhai will hear arguments in Eugene on whether to issue an injunction halting the planned "deep drawdown" for at least one year, as reported by the Tri-City Herald/Statesman Journal. The hearing will also address a dispute over whether the Corps must turn over its internal records to the court and to Marion County, first reported by KATU.

The Corps plans to begin lowering the reservoir anytime between Nov. 1 and Dec. 31, dropping it to 1,425 feet above sea level. That would tie the lowest the reservoir has ever been, matching levels reached in 2015 and 2019, and sit 25 feet below where it normally rests in winter. In future years, the reservoir could drop as low as 1,395 feet under a December 2024 biological opinion from the National Marine Fisheries Service.

The drawdown is meant to help juvenile spring Chinook salmon that hatched upstream of Detroit Dam navigate the reservoir and migrate out through the dam's base.

Marion County Commissioner Kevin Cameron said the plan does not comply with the law. "Our goal is to protect our community's clean water for drinking, irrigation, recreation and fish," Cameron said. "Because the Army Corps' current plan does not comply with the law, there should not be any deep drawdown of Detroit Lake this year."

Salem and Marion County argue the Corps skipped a turbidity study that Congress required after a 2023 drawdown of Green Peter Reservoir caused massive sediment problems. That drawdown disrupted drinking water in Sweet Home and Lebanon and flushed millions of kokanee salmon downstream. The popular fishery has not recovered. Congress set a Jan. 4, 2026, deadline for the study. The Corps missed it.

Salem's slow-sand filtration system works best when turbidity stays below 10 NTU, a measure of water clarity. During the Green Peter drawdown, turbidity hit 2,700 NTU.

The city has spent nearly $8 million over the past 18 months building backup water sources, including new groundwater wells on Geren Island, an aquifer storage facility in South Salem and an emergency connection with Keizer, according to a City of Salem press release.

Salem City Manager Krishna Namburi said in an Aug. 21 statement that the risks need to be addressed before the drawdown proceeds.

The city is also asking the judge to require the Corps to pause the drawdown if sediment levels in the North Santiam River reach thresholds that would shut down Salem's water treatment.

The Corps argues in court documents that Salem and Marion County have not shown they will suffer irreparable harm or that they are likely to win on the merits. The agency says it plans to lower the reservoir slowly, monitor turbidity and would "pause, modify or cease the deep drawdown if necessary."

The Native Fish Society intervened in the case in support of the Corps. Legislative director Jennifer Fairbrother said federal fisheries scientists have called for safer salmon passage past these dams for nearly 20 years.

NOAA forecasts an 81% chance of a very strong El Niño from October through December 2026, according to Marion County. The county warns those conditions could prevent the reservoir from refilling after a drawdown. The Corps' own analysis found that the level of low rainfall that causes water shortages when combined with a deep drawdown occurs one out of every four years.

Marion County filed its lawsuit on May 13. Salem filed separately on July 8. A coalition letter sent June 22 opposing the drawdown was signed by the cities of Stayton, Sublimity, Mill City and Idanha, along with the Detroit Lake Foundation, Detroit Lake Marina, Woodburn Area Chamber of Commerce and North Marion Tourism Collaborative.

Judge Kasubhai's ruling could come shortly after the Tuesday hearing. If he sides with the Corps, the drawdown would begin as scheduled this fall.