Water Lily Removal on Beaver Lake Postponed until Thursday

Release Date: September 18, 2017

Due to expected rain on Tuesday, water lily removal has been rescheduled to Thursday, September  21.

Non-native, invasive Nymphaea Odorata (Fragrant Water Lily) removal on middle, upper, and lower Beaver Lake has been rescheduled to Thursday, September 21.  Lake property owners have been notified consistent with noticing requirements of the approved Department of Ecology Permit No WAG99419. Shoreline notification signs will be placed the day prior to water lily removal. Forecast of rain or wind may affect removal date.  

Responses to Frequently Asked Questions (FAQ) have been developed. Please see the FAQ link

For more information, please contact:


Chris Knutson

Water Quality Planner/Project Manager II

King County Water and Land Resources Division

201 S. Jackson St, Suite 600

Seattle, WA 98104-3855


206-477-4739 (office)


Informational Update on Non-native Invasive Water Lily Removal on Beaver Lake

Release Date: August 08, 2017

The Beaver Lake Management District (BLMD) has postponed the removal of non-native, invasive fragrant water lilies to better inform Sammamish residents on its impacts to Beaver Lake and the use of glyphosate for its removal.

Fragrant water lily (nymphaea odorata) is a King County listed noxious weed. In the last few years, the BLMD has identified the increased abundance of this listed noxious weed as a primary concern of Beaver Lake residents.  The invasive lily has several negative impacts to the lake ecosystem and recreational uses including: increased water temperature, reduced dissolved oxygen, likelihood of increased harmful algal blooms, poor habitat for native fish, risk of entanglement for swimmers (including confirmed deaths on other lakes), fouling of boat motors, etc.  

If left untreated, safety, recreational uses, and water quality in Beaver Lake will be affected. Several options for treatment of the lilies exist including mechanical removal, rotovation, bottom barriers, weed rollers, hand cutting and herbicide.  After consideration of these methods, it was determined that using glyphosate as a foliar treatment on the lily pads was the preferred option. This is the most commonly used approach to control large scale infestations. The estimated 5 acres of lilies on the lake were too large for the other alternatives to be feasible (although they may be used in the future if the overall population is reduced to a manageable level).

Last year (2016) the Beaver Lake Community Club applied for and received a permit to treat a portion of the lilies with glyphosate (only the shoreline of Community Club members). Several meetings were held at the Beaver Lake Lodge to discuss the treatment options. After discussion, they decided to proceed with the treatment and also decided to take the additional step of collecting several water samples 48 hours after the treatment to analyze for residual glyphosate in the water. Those samples were collected in locations where the herbicide was applied and all samples came back from the laboratory negative for glyphosate (below the method detection limit). This helped reassure the community members that they were not exposed to residual herbicide while recreating in the lake.

One of the reasons glyphosate is a preferable herbicide is that it is applied directly to the exposed leaves versus having to apply the chemical directly to the water like some other alternatives. This also helps reduce the potential exposure to people and other organisms. Although inevitably some herbicide will contact the water, glyphosate is not very mobile. It readily bonds with sediment particles and degrades quickly though microbial activity.

The use of glyphosate for this purpose has been reviewed federally by the Environmental Protection Agency (EPA), Washington State Department of Agriculture, and the Department of Ecology. Glyphosate was found to present a low hazard to public health and wildlife. The aquatic version has very minimal use restrictions which include no swimming or watering restrictions immediately after application and a 48 hour drinking restriction (or until concentrations below 700 parts per billion).  Under Permit No. WAG994319, the EPA and Washington State Department of Ecology have approved the product Rodeo (active ingredient glyphosate) to treat the invasive fragrant water lilies on Beaver Lake.

As lake residents ourselves, the Lake Management District Board shares your concern for our residents' health as well as that of the lake. We also greatly appreciate your ongoing feedback including opinions against using the treatment and considered it along with all the other information we have reviewed. However, given the information described above, we believe proceeding with the herbicide treatment at Beaver Lake is the best course of action we can take it is beneficial to the lake and protective of the health of its residents. We plan to move forward with the treatment in the near future. We will adhere to all the state requirements regarding treatment, monitor the effectiveness, and keep the community informed.

Thank you for your ongoing interest in Beaver Lake.


The Beaver Lake Management District Board


Below are several links to Department of Ecology and King County Websites that detail the issues related to fragrant water lily and glyphosate.






 *The Washington State Department of Ecology will be releasing a new Environmental Impact Statement on glyphosate the week of August 14th. Please see the website below after that date to review the document.



See Approved DOE Permit No. WAG994319 below.


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