This Class B noxious weed is widespread throughout Washington State. Control is not required but recommended in King County. This species is also on the Washington quarantine list (known as the prohibited plants list) (external link) and it is prohibited to transport, buy, sell, offer for sale, or to distribute plants or plant parts of this species, into or within the state of Washington. It is further prohibited to intentionally transplant wild plants and/or plant parts of this species within the state of Washington.
Eurasian watermilfoil is a submerged aquatic plant that is present in many lakes in King County, especially lakes with public boat launches. In order to prevent further spread of this and other aquatic weeds, boaters should clean all vegetation from boats and trailers before moving between lakes. If Eurasian watermilfoil is detected early enough, it may be possible to control it.
Additional information on Eurasian watermilfoil
What to do if you find this plant in King County, Washington
Because Eurasian watermilfoil is so widespread, property owners in King County are not required to control it and we are not generally tracking infestations. We can provide advice on how to control Eurasian watermilfoil, but there is generally no legal requirement to do so.
Milfoil impacts - click thumbnail for larger image