Managing invasive aquatic noxious weed populations in the Arboretum wetlands

What’s going on in the Arboretum Wetlands?

Seattle Parks and Recreation is actively managing invasive aquatic noxious weed populations in the Arboretum wetlands along the Arboretum Trail and non-native trees adjacent to Arboretum Creek where Lake Washington Blvd intersects Lynn Street at the Wilcox Footbridge, extending to the South Stone Bridge.  

The weeds are growing so fast that they are displacing newly planted native plants, degrading the wetlands and habitat quality for local fish and wildlife.

The invasive plants we are controlling are:

  • Reed Canary Grass
  • Tree of heaven
  • Himalayan blackberry
  • Hedge bindweed
  • Bittersweet nightshade
  • Invasive European tree species

Weed leaves and stems will be treated with an aquatic-use herbicide containing either imazapyr or triclopyr. Trees will be treated by injection of imazapyr. These products have been approved and permitted for this use by Washington State Department of Ecology.

Intermittent treatments will occur the week of September 30th.

Treatment areas will be clearly marked and temporarily closed to public access. This is being done so that work can be completed quickly and efficiently. The areas will reopen the morning after treatments are complete.

There is no risk to humans, animals, birds, and other wildlife before, during or after; the treatments and pose no hazards to nearby habitat areas, beaches, parks and other recreational sites.