The decline of native salmon and steelhead in the Willamette River Basin has been documented for decades, but this year brought particularly bad news.

Wild steelhead returned to rivers such as the North Santiam and Molalla at such low numbers state biologists said basin-wide extinction was a real possibility.

Meanwhile, wild chinook numbers haven’t improved after being listed as “threatened” in 1999 under the Endangered Species Act.

The response to what many view as a crisis has included an array of options this year, from removing sea lions that prey upon fish to ending the practice of stocking rivers with hatchery-raised species.

But on Thursday, three conservation groups took aim at what they say is the biggest culprit in the decline of native fish — dams.

More on steelhead:Steelhead runs plummet to historically low levels on Santiam, Willamette

The Native Fish Society, Wild Earth Guardians and Northwest Environmental Defense Center issued a notice of intent to sue the U.S. Army Corps of Engineers over what they’re calling the agency’s failure to improve dam passage for adult and juvenile fish.

They say the Corps has consistently missed deadlines or dragged its feet in meeting requirements to improve habitat conditions following a 2008 legal agreement.

“Upper Willamette salmon and steelhead are at risk of becoming extinct and the dams are a primary threat,” said Conrad Gowell, River Steward Program Director for the Native Fish Society.

“There were agreed upon actions the Corps were legally required to take, and they’ve either showed a pattern of delays or just missed deadlines, at the same time these endangered species have continued to decline,” he said.

The groups say Cougar Dam, on the McKenzie River, was supposed to have downstream fish passage by 2015, but that won’t happen for years. The Corps also is postponing efforts to improve passage and water temperatures at the Middle Fork Willamette dams, the lawsuit says.

It's not the first lawsuit to be filed against the Corps in 2017. This spring, two environmental groups sued to Corps in an effort to get them to stop funding stocking of hatchery-raised summer steelhead into the Upper Willamette system.

Corps spokesman Tom Conning said the agency is committed to actions beneficial to fish, but they have to balance it with what’s “technically feasible and cost-effective.”

Related:Report: Sea lions push Willamette River steelhead to brink of extinction

Conning said the agency has spent $194 million to improve habitat conditions and fish passage in the North Santiam, South Santiam, McKenzie and Middle Fork rivers.

(See the list of examples below).

“While (there is) focus on the needs of the fish, we continue to balance flood risk management with hydropower generation, irrigation, water quality, fish and wildlife, and recreation,” he said.

More on steelhead:North Santiam's summer steelhead run faces uncertain future

Gowell said the lawsuit was a “last resort” and that he hoped the notice would restart an emphasis on improving conditions for fish.

“We’ve reached a point where we can’t wait another 10 years,” he said. “We need to take action now.”

List of Corps projects since 2008 agreement on improving conditions and endangered fish

North Santiam:

• Adult Upstream Passage – Minto Adult Fish Collection Facility (2012)

• Interim Temperature Control through Operational Modifications at Detroit (2009)

• Design underway for Long-term Temperature/Downstream Passage at Detroit (ongoing)

South Santiam:

• Adult Upstream Passage – Foster Adult Fish Collection Facility (2014)

• Extended Foster Dam Fish Weir Ops (2013)

• Downstream Fish Passage Spillway Weir Modifications at Foster Dam (2017)

More on steelhead:Lawsuit seeks elimination of summer steelhead on Willamette, Santiam rivers

McKenzie:

• Temperature Tower at Cougar (2005)

• Adult Upstream Passage – Cougar Adult Fish Collection Facility (2010)

• Downstream Passage Testing with Portable Floating Fish Collection (PFFC) at Cougar (2014)

Middle Fork:

• Adult Upstream Passage – Fall Creek Fish Collection Facility Design (Construction – FY16/18)

• Downstream fish passage through Fall Creek Drawdown (2009)

• Completed alternative evaluations for Dexter Adult Fish Collection Facilities

• Implementation of Middle Fork Willamette RM&E Plan (2017)

Habitat:

• Habitat Technical Teamwork ongoing – land purchases/habitat restoration funded

Zach Urness has been an outdoors writer, photographer and videographer in Oregon for nine years. He is the author of the book “Hiking Southern Oregon” and can be reached at zurness@StatesmanJournal.com or (503) 399-6801. Find him on Twitter at @ZachsORoutdoors.