Portland, Ore. – This fall and winter, residents living near Cougar, Green Peter, Lookout Point, and Fall Creek reservoirs should expect lower water levels as part of an effort by the U.S. Army Corps of Engineers (USACE) to support the recovery of endangered fish.
The lower reservoir levels, or “drawdowns,” are a critical element of the 2024 National Marine Fisheries Service’s Biological Opinion (BiOp), which aims to help endangered salmon exit the reservoirs through the dams to migrate downriver.
“Spring Chinook salmon are surface-oriented, so lowering reservoir levels closer to the dam outlets improves their ability to move out of the reservoir and downstream,” said Kathryn Tackley, a program manager at the Portland District who is working to implement the BiOp.
As part of their lifecycle, salmon and steelhead hatch in the river and then migrate downriver to the ocean, where they stay several years before returning to the river where they hatched. USACE’s Willamette Valley dams, which were constructed primarily for flood risk reduction, block the migration routes salmonids take during their lifecycle.
Tackley said these drawdowns should be considered the “new normal” for these reservoirs until USACE constructs physical fish-passage structures to replace the need for the drawdowns.
USACE will adapt the timing of the drawdowns to the weather and river conditions.
Residents can track real-time reservoir levels on the USACE “teacup diagrams” webpage, which will show daily water elevations for USACE-managed reservoirs.
Water Quality
In 2023 and 2024, deep reservoir drawdowns at Green Peter caused noticeable sediment movement downstream, which affected some water treatment facilities.
Increased turbidity may occur again during the 2025 drawdowns and USACE will continue to work closely with drinking water facilities during these operations.
"We are committed to balancing the needs of the communities with our responsibility to protect endangered species," said Col. Dale Caswell, the commander of the Portland District, U.S. Army Corps of Engineers. "During these drawdowns, we will continue to coordinate with downstream communities and state agencies to monitor and address drinking water concerns."
Detroit Drawdown Update
The 2024 BiOp calls for a deep drawdown at Detroit Reservoir to improve downstream fish passage.
USACE delayed the deep drawdown at Detroit until 2026 so that it can first perform and finalize a study – a “Supplemental Environmental Impact Statement” – that will analyze potential effects of the drawdown and get public input on the drawdown.
Recreation and Safety During Drawdowns
Drawdown measures will temporarily close some local boat ramps through February.
The Portland District encourages the public to check boat ramps availability at the “teacup diagrams” webpage before heading out to recreate. Users can click on the red dam icons to find boat ramp elevations shown alongside reservoir water elevations.
Beginning in October, the public should refrain from recreating in the reservoirs due to the drawdowns. Additionally, downstream recreators should use caution as suspended sediment and woody debris are likely to be dislodged during drawdowns, causing low visibility and difficulties in seeing submerged obstacles.
The lower reservoir levels may also uncover unknown hazards as the lakebed is exposed.
“The newly exposed areas of the lakebed may be soft and muddy,” said Christie Johnson, a Corps park ranger. “There have been several incidents in the past where people and pets have gotten stuck in the mud and required rescue.”
During the deep drawdowns, USACE will continue its mission to protect cultural and historical sites on federal land, and visitors are prohibited from collecting, excavating, removing, damaging or disturbing resources – such as artifacts, sites or resources of any kind, including rocks – from the lakebed.