Aquatic Weed Management Program in 2026 

Seattle Parks and Recreation (SPR) will continue the integrated weed management program at selected lakefront properties on Lake Washington this June and July. This program helps control invasive and noxious aquatic weeds, including Eurasian milfoil, Egeria, fragrant water lily, and pond weeds. 

Controlling these weeds improves water quality and recreational access and safety at freshwater beaches, swim areas, moorages and other high-use recreation locations along the lakes. This weed control creates a more natural, aesthetically appealing environment that nourishes native plant growth and aquatic species with the proper water temperature and oxygen level.   

Hand cutting, and manual removal of the weeds will continue as in past years. SPR will complement this work by using selected aquatic herbicides. This use is permitted by Washington Department of Ecology (Ecology). These herbicides have been screened and endorsed by Ecology as an effective solution to control these noxious and invasive weeds.   

SPR has contracted with AquaTechnex, LLC to apply the selected non-glyphosate aquatic herbicides along the shore of Lake Washington at the following locations: 

Eurasian Milfoil Treatment 

June 23–24, 2026 (7 AM – 3 PM) 

• Madrona Beach 
• Mt. Baker Beach 
• Pritchard Island Beach 
• Seward Park Swim Beach 

There are no swimming or fishing restrictions associated with this treatment. Visitors are asked to remain at least 50 feet away from AquaTechnex boats while treatment activities are underway. 

Egeria, Pond Weed, and Fragrant Water Lily Treatment 

July 27, 2026 (7 AM – 3 PM) 

• Matthews Park beach  
• Prichard Island Beach  
• Stan Sayers Pits   
• Seward Beach 

This treatment requires a 24-hour swimming and boating closure beginning at the time of application.  

Informational signs will be posted near the treatment locations prior to treating the plants and appropriate safety precautions will be taken to ensure that there will be no exposure to park visitors, pets, and wildlife.    

The work is being performed under a permit from the Washington State Department of Ecology.   

For more information, please contact Bridget Kelsh at Bridget.kelsh@seattle.gov.For information about aquatic noxious weed control permits visit: https://ecology.wa.gov/Regulations-Permits/Permits-certifications/Aquatic-pesticide-permits/Aquatic-noxious-weed-control.