Aquatic weed treatments week of July 16th

Aquatechnex will be treating invasive and nuisance aquatic weed growth that is interfering with swimming and boating sites on Lake Washington the week of July 16th under a permit from the Washington Department of Ecology.  The schedule will be as follows:

Tuesday July 16th, Stan Sayers and Seward Park

Wednesday July 17th, Matthews Beach, Madrona Beach

Thursday July 18th, Madison Beach, Magnuson Beach, Leshi Marinas

Friday July 19th, Mt. Baker Beach, Prichard Beach, Lakewood Marina

Dense aquatic weed growth is both a threat to swimmers and an impairment to rescue workers during swimming emergencies.  The objective of these treatments is to limit the impact of this growth within high use areas and communities beaches to improve safety.

Questions can be addressed to the City Parks Department or Aquatechnex at 360-527-1271 or


2018 Treatment Program is announced

The first treatment for invasive Eurasian Milfoil at the Seattle Parks beaches and moorages on Lake Washington will be performed on Wednesday May 23rd.  Each location will be posted prior to treatment with water use restrictions.  There is a 24 hour swimming precaution required by the DOE permit and the beaches will be closed for this activity the day of treatment

A treatment map can be viewed at May 23rd Treatment Map

The water use restrictions apply within the yellow treatment polygon and within the blue buffer that extends 400 feet in each direction.

The treatments will start at Matthews Beach on the north end, and end at Prichard Beach in the south.  You may have to zoom in on the treatment map to search location.  You may also enter your address in the top right corner and determine if your home is within a treatment zone.

Eurasian Milfoil Treatments to Happen Wednesday, May 31st

Aquatechnex biologists will be treating the harmful introduced aquatic plant species Eurasian Milfoil at a number of Park Beaches on Wednesday, May 31st.  Eurasian Milfoil poses a threat to swimmers and can also impact rescue efforts if a swimmer is in trouble.

We will be using a US EPA and Washington Department of Ecology approved product that selectively targets this invasive aquatic species.  On Tuesday we will be posting signage at park locations where treatment will occur.  There is a 3 day restriction on drawing water from the treatment area of the lake to irrigate.  There is also a 24 hour swimming precaution and the City will be closing the beaches for this period.

The treatment map can be viewed at

You can zoom into a location and view it.  You can also enter an address and zoom to that location to see if this affects your property.  The yellow treatment polygon shows area to be treated.  The blue buffer polygon shows WA DOE Required Water Use Restriction Zone.  The restrictions that will be posted on lake shoreline areas within the blue buffer are a 24 hour swimming precaution and a 3 day irrigation restriction if you draw lake water to irrigation with.

Integrated Aquatic Weed Management Program for 2017

This summer, Seattle Parks and Recreation (SPR) will begin an integrated aquatic weed management program to control Eurasian Milfoil and fragrant water lily infestations at its lakefront properties on Lake Washington.

Controlling these weeds will improve water quality and recreational access at freshwater beaches, swim areas, moorages and other high-use recreation locations along the lake.

Mowing, hand cutting, and removal of the weeds will continue as in past years.  SPR will complement this work by using selected US EPA and Washington DOE approved aquatic herbicides.  This use is permitted by the Washington Department of Ecology (Ecology).  These herbicide 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 herbicide.  This web page will be used to communicate with interested parties. A interactive ArcOnline web map will be added as soon as sites are finalized.  This page will also be updated just prior to treatment to inform the public as to where actions are occurring.