Olympic Invasive Working Group (OIWG)

The Olympic Invasive Working Group (OIWG) is a loose-knit consortium of about 20 government agencies, tribes, non-profits, and private landowners, all working to eliminate invasive knotweed from waterways on the Olympic Peninsula. The group has met twice a year since 2005, to share information and work together to control knotweed. Clallam County Noxious Weed Control Board (CCNWCB), as the unofficial group leader, coordinates the meetings and supports the work of other group members.

Meetings are usually held in the spring and fall and minutes are kept and sent out to interested parties. OIWG members give reports on their activities and experts in the field are invited to present at our meetings. 

OIWG members have worked in all the major rivers on the Olympic Peninsula, and knotweed populations on most Clallam County rivers have been reduced by 90%! However, it is important to keep monitoring and controlling the few plants that do appear, otherwise plants will spread and all our hard work will be undone.

This map shows the scope of work undertaken by OIWG partners on the Olympic Peninsula in 2021.

OIWG Knotweed Points 2021

This map shows the amount of knotweed observed on the Olympic Peninsula in 2015.

Knotweed Map

Crew Member with Knotweed

Crew Member with Knotweed

Large Knotweed Patch After Herbicide Treatment

Dead Knotweed


The Hood Canal Coordinating Council is an active partner, which tracks knotweed control projects in the Hood Canal region and maintains records. Both Jefferson County's Noxious Weed Control Program and Mason County's Noxious Weed Control Program work closely with Clallam County in knotweed control.