Marian Hanson transplants plants to accommodate the lack of shade because of a fallen tree at the Adopt-A-Stream Foundation in McCollum Park in Everett.

EVERETT — More than 20 years after drawing up a master plan, the Northwest Stream Center is preparing to open this summer.

The center, a project of the Adopt-a-Stream Foundation, has a few things left to do before formally opening its doors.

That’s probably news to the hordes of schoolkids who already have taken tours of the site and marveled at the underwater views of cutthroat trout or the blooming skunk cabbage in the 20-acre wetland in Snohomish County’s McCollum Park.

“We want to get everything ready,” said Tom Murdoch, the executive director of the foundation. “We’re not quite ready to accommodate the general public right now.”

The projected opening date is late spring or early summer, he said, but that’s dependent on a number of things being accomplished, many of which rely on volunteer labor and the arrival of donated materials and funds.

There are a large number of interpretive signs, for example, but the posts and frames haven’t arrived yet, Murdoch said.

Lighting still needs to be installed along the walkway. Viewpoints along the raised boardwalk that winds through the wetland are built when sponsors come forward with the necessary support.

There are a lot of opportunities for sponsorships, Murdoch said.

The Trout Stream exhibit, for example, has received about $1.5 million in donated materials, supplies and labor from 51 companies and organizations. The exhibit includes underwater viewing windows into an active trout stream, allowing visitors to watch wild cutthroat trout, freshwater mussels, crayfish and other animals in their natural habitat.

The elevated boardwalk was a multiyear effort that started out with bushwhacking through the swamp to lay out the route, removing valuable plants for repotting elsewhere on the site, and clearing out invasive species.

Thousands of plants were removed, including 50 to 60 large skunk cabbages, whose roots go down two feet.

“Most of the work was done wearing chest-waders and up to our shoulders in muck,” Murdoch said.

The boardwalk is made of recycled plastic lumber, and with more than 5,000 deckboards, it took over 10,000 hours of donated labor to build and install.

Murdoch credits two volunteers in particular with the work: Larry Gearheard, who assembled much of the walkway, and Marian Hanson, who repotted thousands of plants and kept the area clear of invasive species.

“We call her the swamp lady,” Murdoch said. “Marian was often out here fine-tuning the naturescape around the boardwalk,” he said.

Without the volunteer help over the years, none of this would have happened, he said.

Chris Winters: 425-374-4165; cwinters@heraldnet.com. Twitter: @Chris_At_Herald.