Tentative review to reconnect Spirit Lake to North Fork of Toutle River after 4 decades
The U.S. Forest Service is considering removing debris from the 1980 Mount St. Helens eruption that has been blocking Spirit Lake from flowing into the North Fork of the Toutle River for more than four decades.
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The strategy aims to address the lake's deteriorating, manmade outflow tunnel that protects an estimated 50,000 people downstream from floods by creating a new way for the lake's excess water to drain.
However, the connection to the North Fork of the Toutle River could take decades to fully form and the draft plan has no absolutes on the channel's creation.
First, crews plan to build another way for the lake's water to flow out, this time inside a pressure tunnel, and repair the current tunnel, creating necessary redundancy and a precise way to control lake levels, the draft plan states.
The blast's debris blocked the lake's natural outflow to the North Fork of the Toutle River after the 1980 Mount St. Helens eruption, while the eruption's sediment raised the lake's floor bed, creating the likelihood of the body of water at the top of the mountain spilling over the debris, causing catastrophic flooding and mudflows onto the communities below.
Now, officials say that the original 41-year-old outflow tunnel - created as an emergency measure - has the capacity to hold less water after years of cracking and moving rocks and needs to be repaired again. Twice since construction completed in 1985, the tunnel completely closed for service as water levels neared the breaching point of above 3,460 feet of elevation, according to the Forest Service's July report.
Mount St. Helens tunnel
Workers from the U.S. Army Corps of Engineers inspect the Spirit Lake drainage tunnel in 2015. They're standing on a section where earth movement had raised the floor nearly 2 feet. Issues such as the floor bed raising has prompted the U.S. Forest Service to review how to fix the 41-year-old structure.
Restoring the natural channel will also allow for more fish passage, but likely increase the amount of sediment downstream in the Cowlitz River, which local leaders have already said needs dredged today.
The Forest Service oversees the lake's tunnel, with the help of U.S. Army Corps of Engineers and U.S. Geological Survey.
People can comment on the draft decision, released Tuesday, through late summer.
The draft plan
The lake's current outflow tunnel needs repaired, according to the project's Final Environmental Impact Statement released this month.
The draft plan selected by Forest Supervisor Johanna Kovarik combines several options:
- repairing the existing 8,465-foot tunnel, which flows into South Coldwater Creak, to use as backup outflow,
- removing the lake's 1980 eruption debris to form possibly form a natural channel to reconnect the lake to the North Fork of the Toutle River downstream, opening decades of lost fish habitat, and
- creating a secondary pressure tunnel - which uses hydraulics instead of the current use of gravity to manage the amount of water that leaves the lake - to use as the main outflow with more precise control.
The draft plan states the new tunnel will be 11 feet in diameter, like the existing passage, and located next to the current tunnel on Harry Ridge.
Experts estimate it would take a little over three years to build.
Draft Record of Decision for Spirit Lake tunnel
Effects of creating a natural channel
The natural channel, however, would take much longer to form, an estimated 10 to 20 years.
If the natural channel does form, wildlife would greatly benefit. The cutthroat trout, rainbow trout and sculpins that live downstream could move to more water systems, the report states.
But breaching the debris would release Spirit Lake's cold water over four existing ponds in the Pumice Plain, which could affect wildlife, the report continues. The temporary drawdown of the lake would briefly expose its shores, where aquatic life lives today.
An estimated 1.8% more sediment could also be released into the Cowlitz River while the channel is being formed, then 0.9% once the channel is in use. The Environmental Impact Statement calls this "a minor effect."
However, city leaders in Longview, Kelso and Castle Rock said in December that sediment continuing to pile in the Cowlitz River has increased the need to dredge it to prevent flood risks. The U.S. Army Corps of Engineers says Congress has not OK'd such a request.
Instead, to prevent more sediment from reaching the Cowlitz, the Corps is preparing to raise the level of the dam on the North Fork of the Toutle River, which was built to prevent sediment from flowing downstream.
The floor bed of this Sediment Retention Structure, about 20 miles south of Spirit Lake, has also risen 100 feet since it was built in 1989, due to piling sediment, making it less effective. Now about 80% of sediment passes through to the rivers downstream.
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Issues surrounding the existing tunnel
After the May 18, 1980 eruption, the geography of Spirit Lake changed.
A massive landslide raised its bed by 200 feet. The surface area also expanded from 1.9 to 3.5 square miles, according to the July report.
With the lake's natural outflow blocked by the landslide, experts estimated the lake could overflow, prompting a federal emergency declaration in 1982 to construct today's deteriorating tunnel, which was built from 1984 to 1985.
Until construction was complete, an emergency temporary pumping facility was built and used.
Twice, the tunnel completely closed for repairs and neared the breaching level: in 1995-96 and 2016-17.
Mount St. Helens tunnel
On the snowy foothills near Mount St. Helens, project manager Brad Neu explains in 2016 how sections of steel ribs will be assembled inside the Spirit Lake tunnel to shore it up. The 41-year-old structure needs more repairs today, experts say.
After the tunnel floor rose through rock movement during the last repair, Congress requested that the Forest Service and other agencies work on a long-term fix.
Originally, 550 cubic feet per second of water could flow through the tunnel, but now only 400 cubic feet per second can pass through a constricted 300-foot section of the tunnel.
It is also difficult to reach the current tunnel.
Officials have to walk 250 feet from a staff parking lot, and cross a waterfall stream to reach the outlet. They have to use a helicopter or boat to reach the intake portion at Spirit Lake, which can be especially dangerous during the winter to open and close the tunnel gates.
To inspect the current tunnel, officials take up to 10 utility-terrain vehicle rides, up to seven boat trips from Duck Bay, and up to three flights a year, according to the report.
Spirit Lake Final EIS
Making the Truman Trail road permanent
Part of the draft plan includes building a 16-foot-wide temporary road to haul material to help form the natural channel, then removing the road when the work is done.
The Forest Service is completing a separate project to replace the gate at the tunnel's intake, which also created a temporary road along the Truman Trail.
However, the work on the tunnel and natural channel will make the Truman Trail road permanent, according to the draft plans.
A coalition of researchers and conservation organizations in 2021 challenged the plan to build the Truman Trail road, saying the Forest Service has not done the proper environmental assessments or adequately weighed the importance of research on the monument or the damage the road will cause.
However, the U.S. District Court for the Western District Court of Washington ruled in favor of the Forest Service in 2022, and construction of that 16-foot-wide Truman Trail road began in 2024.
The Truman Trail was originally built to help crews create the emergency pumping site needed while the existing tunnel was being built.
The new intake gate is expected to be completed in 2027, but has no effect on the failing parts of the tunnel to be addressed in the latest draft plan.
How to comment
Comments about the plan can be sent to:
Kelsey Jolley, Spirit Lake NEPA Coordinator
Gifford Pinchot National Forest All Units
987 McClellan Rd., Vancouver, WA, 98661
OR
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This story was originally published July 11, 2026 at 6:27 PM.