EVERETT — Spencer Island is a haven for threatened Chinook salmon.

At the brackish heart of the Snohomish River estuary, the combination of fresh and salty water helps young Chinook prepare for their journey to the ocean.

“It’s critical,” said Mike Rustay, senior habitat specialist for Snohomish County.

Chinook salmon, which have declined 60% in the Salish Sea since the mid-1980s, are a linchpin piece of Puget Sound’s ecosystem. They’re also the favored dish of critically endangered Southern Resident orcas.

Spencer Island is a popular spot for birdwatching, hunting waterfowl and hiking, as well. As several groups start to plan a restoration project for the area, they want to consider both the people and wildlife who use it.

The state Department of Fish and Wildlife, in partnership with Snohomish County and the U.S. Army Corps of Engineers, is seeking public input on the project. At this stage, residents mainly seem concerned about how the $9 million project will affect the island’s trail network, said Seth Ballhorn, environmental planner for Fish and Wildlife.

Project leaders are considering 10 different designs that involve lowering and breaching dikes, as well as redesigning channels, to restore wildlife habitat on the island.

Some of the design options are especially beneficial to Chinook and other wildlife. But those same designs would also flood a majority of the island’s trail network.

“If folks wanted to off-road with waders, they could,” Ballhorn said, but “the county wouldn’t be maintaining that as a formal trail.”

Fish and Wildlife, and Snohomish County, already struggle to maintain trails on the island because the ground is unstable. Paths were created on former dikes made of wood chips or hog fuel, a wood byproduct, so they are constantly falling apart and sinking.

Spencer Island wasn’t necessarily “a planned restoration” project, Ballhorn said.

In the early 1900s, farmers diked and developed the island, destroying forested wetlands and crucial wildlife habitat. Fish and Wildlife, along with Snohomish County, purchased the property in 1989, with the state agency owning the northern side and the county owning the southern side.

Snohomish County removed sections of dike in 1994, so tidal water and fish could travel into the southern portion of the island. But in 2005, several dikes caught fire and collapsed.

The entire island became flooded.

This wasn’t an entirely bad thing, Ballhorn said, but it created challenges for future restoration efforts. Construction workers will have to use equipment like amphibious excavators, which tread lightly on land and float on water, to access channels and dikes that need to be altered.

Ballhorn led an in-person public feedback session for the project on Aug. 31, but only “a handful” of residents attended, he said. Project leaders hope more residents will share concerns and questions during the online public comment period, so they extended the deadline for participation to Oct. 8.

Fish and Wildlife posted information on its website this week that illustrates how each of the design options will alter trails. Images don’t include boardwalks or viewing platforms that may get built during the project, Ballhorn said.

After the public comment period ends, project leaders aim to have a single preliminary design for the project by early next year.

In 2019, Snohomish County completed a similar restoration project on Mid-Spencer Island — a site just north of the main Spencer Island. Construction workers successfully made multiple openings, or dike breaches, allowing more fish to find habitat.

Rustay said he hopes the upcoming project on Spencer Island achieves the same results.

“As we do more and more of these projects, we’re managing how we construct them, find funding for them and monitor them,” Rustay said. “The next sites we restore are benefited from that.”

Ta’Leah Van Sistine: 425-339-3460; taleah.vansistine@heraldnet.com; Twitter: @TaLeahRoseV.