CLACKAMAS COUNTY, Ore. (KOIN) — The U.S. Army Corps of Engineers will lower summertime water levels in Detroit Reservoir in order to mitigate risk in the unlikely event of a large earthquake, a decision residents and businesses worry will shorten the recreational season.

Detroit Dam is located about 150 miles east of the Cascadia Subduction Zone, a megathrust fault that stretches from Cape Mendocino, California all the way up to Vancouver Island, Canada. The subduction zone is capable of producing magnitude 9 and larger earthquakes approximately every 300 to 500 years.

While Corps officials stress that the dam is in "very good condition," a seismic hazard analysis last year revealed there is a possibility the spillway gate's supporting arms could buckle during such an event, resulting in an uncontrolled release of water. If that happened, it could unleash devastating flooding on large swaths of the North Santiam River canyon and urban areas, including the state capital.

"You're looking at the entire watershed downstream," said Dustin Bengtson, Willamette Valley Project deputy operations project manager for the Corps.

The potential threat to life and property is why Bengston said the Corps needs to err on the side of caution and take immediate action: Lowering the maximum lake level by 5 feet.

Detroit Lake normally fills to 1,563.5 feet at the dam. The Corps plans to lower that level to 1,558.5 feet, which would put less pressure on the dam in the event of a major earthquake. The reduction will likely remain in place for several years as the Corps studies the plan further and determines long term steps, which could include reconstruction of the spillway structure if needed.

Five feet may not seem like a lot, but it's enough to cut the lake's recreation season short. And the lake is the center of Detroit's economy. Read full story