Salem city leaders will receive an update this week on drawdowns to the Detroit Reservoir and how it will affect drinking water for around 200,000 residents.

At a City Council meeting Monday, councilors will receive a supplemental report from Salem Public Works Director Brian Martin that offers more information on drinking water treatment challenges the city can expect in years to come. The Salem Statesman Journal was first to report on the coming update.

In July, City Council voted to approve an emergency declaration as the U.S. Army Corps of Engineers prepares for a deep drawdown of the Detroit Reservoir to help endangered salmon make their way past Detroit Dam. That drawdown would bring the reservoir to its lowest level since the dam was built in the 1950s and release sediment that’s been accumulating for decades.

Though water today remains safe to drink, Salem’s drinking water treatment plant is not designed to handle that level of sediment.

Salem considers declaring drinking water emergency ahead of Detroit Lake deep drawdown

Speaking to OPB in August, water treatment officials in Salem said the city’s emergency declaration allowed it to move faster on upgrades to the treatment plant that will be needed as the Corps of Engineers engages in drawdowns each year, starting in fall of 2026.

The drawdowns are required because NOAA Fisheries indicated in 2024 that salmon and other challenged fish populations are having difficulty making their way downstream to the ocean.

The public works report indicates that city staff learned more about those drawdowns in an Aug. 26 meeting with the federal government.

“At this meeting, the Corps assured the City that it fully understands the potential consequences of the drawdown and indicated its intention to closely monitor levels of turbidity,” a summary of Monday’s report states.

Costly turbidity

Salem’s drinking water facility on Geren Island, near Stayton, relies on slow sand filtration to clean water before distributing it to residents. It measures the amount of sediment in the water using nephelometric turbidity units, or NTU.

“To illustrate: water with turbidity of 10 NTU or less looks clear; water with turbidity of 50 NTU looks cloudy; water with turbidity exceeding 500 NTU looks muddy,” the public works report states.

Salem approves emergency declaration over drinking water

Currently, the Geren Island treatment plant deals with essentially clear water that has 10 NTU or less. At that rate, slow sand filters at the plant can operate for about three months before staff take them offline for cleaning.

The Army Corps of Engineers gathered data from past drawdowns at other reservoirs in the Willamette River system and found that turbidity levels during those operations were sustained above 50 NTU and, in some cases, reached as high as 800 NTU.

Salem’s Public Works Department does not believe the Geren Island facility can sustainably deal with that level of turbidity. The impacts would be costly, according to the report.

Based on testing, the department’s staff estimated that filters intaking water at 50 NTU may only last 21 days before needing to be taken offline. Additionally, the life cycle of the filters would potentially be reduced from four years to just two months.

Replacing each filter would cost the city around $3 million.

What to know about Salem’s water emergency and what’s being done to prevent it

Corps of Engineers officials assured the city in the August meeting that they want to coordinate on the drawdown to try to prevent damaging effects to the drinking water supply and costly damage to the treatment facility. That may mean stepped drawdowns over multiple years or even pausing drawdowns if the water becomes too murky.

Meanwhile, Salem is making progress on measures that could further help the situation ahead of fall 2026. Since the emergency declaration in July, contracts have moved ahead to build up to four new groundwater wells at Geren Island and drilling is already underway.

The Corps of Engineers is expected to release a supplemental environmental impact statement on the Detroit Reservoir drawdown and open a public comment period in late October or early November.

Salem City Council will receive the updated report on drinking water at its regular meeting 6 p.m., Monday. People can attend in person at the Salem Public Library’s Loucks Auditorium, or view the session on YouTube.

News Source : https://www.opb.org/article/2025/09/22/salem-updates-drinking-water-treatment-drawdown/