VERLOT — How do you move a river?

That’s the task crews faced this summer on the South Fork Stillaguamish River, by the Gold Basin Campground.

The answer: A lot of digging.

Workers demolished half the sites at the always-full campground off Mountain Loop Highway, ripping out concrete and fire pits and pit toilets. They logged hundreds of trees and dug a new 2,600-foot channel. Then, in August, they switched the river, like switching directions on a railroad track. As the water drained, they caught and moved hundreds of fish — Coho and juvenile Chinook salmon, rainbow trout, sculpin,lots of whitefish and a single bull trout.

To prevent sediment from sliding into the water, they built a series of barriers along the new channel using 1,600 logs. Behind them are a series of pools separated by small dams. Over a decade or so, they will fill up with silt. And trees will grow, creating a new wetland-type environment that will continue to catch and filter the silt.

The $5.3 million habitat restoration project to help endangered salmon species is an effort that spans 20 years. It involved a partnership between the Stillaguamish Tribe, the Stillaguamish Watershed Council and the U.S. Forest Service, and required a lot of design and labor. Anchor QEA, Oso-based Anderson River Construction, Goodfellow Bros. and union workers contributed to the project.

The work is a balancing act between habitat restoration and recreation. Darrington District Ranger Greta Smith saw it as an opportunity to teach campers about how we can help the environment.

Smith said the U.S. Forest Service is working with the National Forest Foundation’s Treasured Landscape initiative to make improvements along Mountain Loop Highway. She sees the Gold Basin project as a model for future endeavors.

“There’s a lot of potential in this effort,” she said. “We’re not quite done yet.”

The project will help protect the river from the Gold Basin landslide, which for decades has been the biggest source of sediment in the river.

The hillside is made of highly erosive clay, sand and gravel, the product of continental glaciers from more than 10,000 years ago, said Scott Rockwell, a forest and fish biologist with the Stillaguamish Tribe. Back then, this area was under hundreds or thousands of feet of water, he said. Gold Basin was part of a lake bottom.

The glacial soils were dropped in layers that can still be seen today from the campground. After the glaciers retreated, the hillside became exposed to the elements, and subject to erosion. Each year, the hillside has dumped about 40,000 tons of sediment into the Stillaguamish, according to a U.S. Forest Service environmental assessment published in 2018.

The landslides can be dramatic. In 1996, so much silt fell that it blocked the river, temporarily forcing it to go through the campground. And a couple of years ago, Rockwell said he found sediment at the campground, a sign of another large slope failure.

All that fine sand and silt isn’t good for fish, including the endangered Chinook salmon, according to studies. It can plug up gravel beds used for spawning, entombing eggs and suffocating baby fish. It can cloud up the water, making it harder for fish to find food and potentially injuring their gills.

The number of Chinook in the river is “extremely low,” according to a 2009 report published by Snohomish County. The Stillaguamish Tribe had been trying to do something about the Gold Basin landslide for more than two decades, said Shawn Yanity, the tribal fisheries manager.

“We had a lot of ups and downs,” he said. “… It always seems like it’s more of a struggle to do the right thing than doing the wrong thing.”

He said he wants to see a viable economy for salmon again. He wants there to be enough fish for everyone, for both tribal members and for sport.

“Our culture is disappearing with the salmon,” he said. “And that’s something that just isn’t acceptable for us.”

Zachariah Bryan: 425-339-3431; zbryan@heraldnet.com. Twitter: @zachariahtb.