In addition to the monitoring and control of over 5,000 noxious weed infested sites in Thurston County, special projects are also performed by Thurston County Noxious Weeds.

Brazilian Elodea (Egeria densa) Removal - Chehalis River

Brazilian Elodea is a non-native submersed freshwater aquatic plant with a heavy infestation in the Chehalis River. Brazilian elodea can quickly spread creating large patches that grow up to the surface of the water. Established colonies of this plant reduce flow, leading to increased water temperature and low dissolved oxygen levels… a dangerous situation for aquatic animals.

Brazilian Elodea differs from native elodea found in Thurston County's rivers and lakes. It has a bottle brush like appearance and can grow up to the surface in deep water. It forms dense mats enabling it to cover a large area, displacing native plants. 

The origin of this plant in the Chehalis has been traced to Plummer Lake and is thought to have escaped from an aquarium dumped in the lake. Never dispose of aquarium contents in a native water system.

Thurston County has actively managed this invasive species since 1998. Currently, manual removal by snorkelers is the primary mode of management in the Chehalis River and is possible through continual support from Washington State Department of Ecology Aquatic Invasive Species funding.

​Variable-leaf milfoil (Myriophyllum heterophyllum) - Clear Lake & Blue Lake

Variable-leaf milfoil is a Class A noxious weed found in only 4 locations statewide. Thurston County has infestations on two lakes; Blue Lake and Clear Lake. Clear Lake currently has good control of this milfoil, but we are still working towards eradication in Blue Lake. Control efforts have varied over the years, using a combination of herbicidal treatments and manual removal by snorkelers. Continual monitoring and control are possible through Washington State Department of Ecology Aquatic Invasive Species funding.

​Information on Containment Ordinance

If you’re grading, putting in utilities for a development, building a new house, or any other land use activity of this nature, click here regarding the Noxious Weed Containment Ordinance and Knotweed species.