Building like beavers to restore island streams

Published 1:30 am Wednesday, July 22, 2026

This summer, crews with the Vashon-Maury Island Land Trust will head into Upper Shinglemill Creek and try to do what beavers have done for millennia: slow the water down.

The work will begin with the installation of beaver dam analogs — hand-built wooden structures designed to mimic some of the benefits of natural beaver dams, Land Trust Operations Manager Jenny Stamper said.

The structures are meant to slow stream flows, help recharge the island’s aquifer, expand wetland habitat and improve conditions for young salmon and the insects they eat.

The project is one of the first early-action efforts in the Land Trust’s multiyear Watershed Restoration Plan for Judd and Shinglemill creeks, Vashon’s two largest watersheds, Stamper said.

Both waterways support chum and coho salmon and cutthroat trout, while Judd Creek historically supported steelhead, Vashon Nature Center Science Director Bianca Perla said in an email. The headwaters of both watersheds originate in Vashon town, with the divide between them falling roughly near the post office.

“A good proportion of islanders live within these watersheds,” Perla said in an email.

Judd Creek is also the island’s largest freshwater stream input into Quartermaster Harbor, meaning its condition can influence the health of the harbor.

The restoration plan, developed with support from the Puyallup Tribe, King County, the King County Flood Control District and WRIA 9, marks a new phase in the Land Trust’s work, Stamper said.

For decades, the organization has focused on conservation, stewardship and restoration — acquiring and caring for land, managing invasive plants and building public access to natural areas.

Now, with large areas under its ownership or management along both creeks, the Land Trust is turning more attention to the health of entire watersheds.

The work is focused on three basic elements of healthy streams: wood, water and bugs, Stamper said.

In old-growth forests, streams were historically filled with fallen trees and woody debris. Those logs created pools where fish could rest and hide from predators, slowed the movement of water through the system and helped create habitat for aquatic insects.

Those insects matter, too. They are a key food source for young salmon rearing in island streams before they head out to salt water.

Vashon Nature Center has collected salmon spawning data and monitored stream insects since the organization’s founding in 2016, with support from the Vashon Groundwater Protection Committee.

The center’s findings show that island streams continue to support small populations of spawning coho and chum salmon, Perla said. Those populations have remained low since the 1990s, fluctuating somewhat with broader ocean conditions while remaining relatively steady or declining slightly overall.

Cutthroat trout are more numerous and widespread, with both resident and sea-run populations found in Judd and Shinglemill creeks.

Recent Nature Center research has also highlighted the importance of Vashon’s small streams to salmon that are born elsewhere. Juvenile Chinook salmon, which do not spawn in island streams, have been documented leaving larger mainland watersheds and entering Tahlequah, Fisher and Raab’s creeks to feed and rear.

Researchers did not find juvenile Chinook using Judd or Shinglemill creeks, but the Nature Center is conducting DNA tests on juvenile fish found in those waterways to determine whether some may be coho from mainland populations.

“What this shows us is that our streams are not only important to the salmon that spawn here, but also to the survival of other salmon populations that spawn in surrounding mainland creeks,” Perla said in an email.

Vashon’s streams may never host spawning runs on the scale of large mainland rivers, she said, but they could provide valuable rearing habitat during a pivotal stage of juvenile salmon development.

Previous Land Trust restoration projects have also shown signs of success, Stamper said. Following earlier log installations in Shinglemill Creek, the Land Trust recorded increases in B-IBI scores.

The Benthic Index of Biotic Integrity, or B-IBI, measures the abundance, diversity and community structure of stream insects to assess the overall condition of a waterway. Data collected by Vashon Nature Center has helped track those insects before and after restoration work.

The Nature Center’s monitoring places Judd and Shinglemill creeks in fair to good condition — but not excellent condition, Perla said.

One of the most significant pressures on both waterways, particularly Shinglemill Creek, is stormwater runoff.

When rain falls on pavement, roofs and other nonforested surfaces, less water is able to soak into the ground. Instead, it can rush into streams, eroding channels, washing away aquatic insects, salmon eggs and young fish, and carrying pollutants toward Puget Sound.

That runoff also represents water that is not replenishing Vashon’s aquifers. The island is designated by the U.S. Environmental Protection Agency as a sole-source aquifer area, meaning rainfall is the source of the island’s drinking water.

“With climate change, we are predicted to have even more intense storms dumping more water all at once on our landscape,” Perla said in an email. “This means that runoff is a problem to address now and for the future as well.”

The Land Trust’s approach will vary by location, Stamper said. Smaller, flatter reaches of creek are better suited for beaver dam analogs, which can help restore wetland conditions and support aquifer recharge.

Areas with more flow and velocity may call for post-assisted log structures, while lower reaches of Shinglemill Creek, where water moves with more force, may need larger woody debris structures.

The first work in Shinglemill Creek will focus on a fork flowing from the headwaters of Fisher Pond, Stamper said. The project is funded by King County’s Department of Natural Resources.

The protected wetlands around Johnson Pond and across Cove Road are considered important aquifer recharge areas. During rainy months, water moves quickly through drainage ditches near 107th Avenue Southwest and Cove Road before entering the ravine.

The Land Trust hopes to slow some of that flow and expand wetland habitat in the area, Stamper said.

Work is already underway. The Land Trust’s stewardship crew has been thinning trees at the Mary Matsuda Gruenewald Forest on Matsuda Farm, and staff are turning those thinnings into poles that will be used to build the beaver dam analogs.

The timing matters, Stamper said. The area contains high-recharge soils, and installing the structures before fall rains return could help boost aquifer recharge.

Perla said the Land Trust’s increased focus on stream restoration comes at a critical time. The organization now controls enough land in both watersheds to meaningfully affect their future, she said, while heavier storm runoff is expected to place increasing pressure on the creeks.

“If we can start helping our watersheds deal with this increased pulse of water flow now, we can increase these watersheds’ ability to adapt to the changes that global warming is bringing to us,” Perla said in an email.

Holding water on the landscape longer could benefit wildlife while also allowing more rainfall to sink into the aquifer that supplies island residents, she said.

The Nature Center has also begun researching emerging water-quality threats, including PFAS — often called “forever chemicals” — and 6PPD-quinone, a chemical produced from a tire additive that is lethal to coho salmon.

Early pilot testing detected the chemicals in both Judd and Shinglemill creeks, Perla said. A grant from the Rose Foundation will support additional testing over the next year, including research into whether concentrations increase during storms.

The Judd Creek portion of the restoration plan is also taking shape, Stamper said. The Land Trust’s first proposed project there will be off Singer Road, near the site of a planned addition to the Judd Creek Trail system.

The project is expected to focus on areas with year-round water flow on Land Trust property, including primary coho salmon spawning and rearing areas.

To guide the work, the Land Trust’s stewardship team spent the spring walking reaches of Judd and Shinglemill creeks, measuring water depth, taking photos and documenting stream conditions, Stamper said.

That information was sent to Wolf Water Resources, the engineering team helping refine the restoration plan.

The Land Trust is also working with a Technical Advisory Committee, co-chaired by board members Shana Lee Hirsch and Phil Levin, to review project plans and ensure the work reflects current science and regional best practices.

This summer’s work will be monitored after installation. Land Trust staff plan to collect data, measure water temperature and water levels, and adjust the structures as needed, Stamper said.

Perla said that kind of planning and follow-up is particularly important for restoration projects that could influence an entire watershed.

Careful planning, clear goals and monitoring the actual — rather than merely anticipated — effects of the projects will help determine whether the work is succeeding, she said.

“We are happy to see that the Land Trust appears to be incorporating all of these,” Perla said in an email, “which will hopefully increase the chances that these restoration actions will actually benefit island watersheds, wildlife and people.”

The goal is not to install permanent structures, Stamper said, but to restart natural processes — slowing water, building habitat and helping streams hold more of the winter rain that moves through Vashon’s watersheds.