Knotweed Program
Since 2010, the Skagit Fisheries Enhancement Group (SFEG) has led knotweed control efforts across the Upper Skagit Watershed. Working through the Skagit Cooperative Weed Management Area (CWMA), a coalition of 18 federal, state, local, tribal, and nonprofit partners, we take a coordinated, watershed-scale approach to tackling this invasive threat.
On the ground, AmeriCorps members from the Washington Conservation Corps do the work, covering roughly 3,500 acres of floodplain habitat along 30 miles of waterways each season.
What is Knotweed?
Knotweed is a class B weed on the Skagit, Snohomish and Whatcom Counties noxious weed lists. This means landowners are responsible for control. Three species of knotweed (Polygonum spp.) have been found in the upper Skagit River watershed– Japanese, Giant, and Bohemian. Knotweeds are perennial plants native to Asia, but in the past were planted in the Pacific Northwest as ornamentals. They have since escaped cultivation and wreaked havoc on our natural ecosystem. Common names include Mexican or Japanese bamboo, elephant ear, or fleece flower.
Scientific Names include: Polygonum cuspidatum, Polygonum sachalinense, Polygonum x bohemicum.
Why is it a problem?
A healthy river ecosystem depends on native plants, and knotweed puts that at risk. Left unchecked, invasive species can overwhelm native vegetation, stripping away the habitat that fish, birds, and other wildlife rely on.
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What makes knotweed so difficult to control isn’t just how fast it grows; it’s how easily it spreads. A single fragment washed downstream in a flood, carried on a tire, or moved by a piece of equipment can take root and start a new infestation. Once established, knotweed doesn’t share space. It forms dense stands that shade out everything around it, and nothing can survive underneath.
That’s a problem with consequences that impact the entire ecosystem. Studies show that streams choked with knotweed have fewer macroinvertebrates, the small aquatic insects at the base of the food web that juvenile salmon rely on. Less insect life means less food, and less food means fewer fish making it to adulthood.
Winter makes things worse. When knotweed dies back seasonally, it leaves bare ground exposed just as winter rains kick in and salmon head upstream to spawn. Without plant roots holding soil in place, rainfall washes sediment directly into streams, smothering the gravel beds where salmon lay their eggs.
Over time, knotweed also prevents forests from recovering. Native trees can’t establish in infested areas, and without trees falling into streams, waterways lose the logs and structure that create the diverse habitat juvenile salmon need to hide, rest, and feed.
The result is a slow unraveling of the riparian ecosystem, one that affects not just plants, but fish, wildlife, and the health of the watershed as a whole.
