Aquatic invasive weed control in Lake Pend Oreille

By Jennifer Ekstrom
Reader Contributor

When I started working to protect water quality in Lake Pend Oreille in 2009, our community was highly concerned about chemical herbicides being sprayed in the water in attempts by public agencies to eradicate eurasian watermilfoil. In the following years, flowering rush was added as another targeted aquatic invasive weed. People were concerned about the impacts the herbicides might have on human health and aquatic life, and also about the dearth of information available to the public prior to the chemicals being added to the water. Chemicals were being applied near drinking water intakes and public beaches with very little public notification. 

Due to endless pressure applied by the Idaho Conservation League and Lake Pend Oreille Waterkeeper (which I worked for at the time), we gained cooperation from the Idaho State Department of Agriculture to avoid using the most toxic herbicides and avoid applying herbicides near drinking water intakes and swimming areas. We also worked hard to gain a common understanding that in a water system as large as Lake Pend Oreille, eradication was a futile notion. At best, invasive weeds could be controlled, but never fully eradicated. Weed control by means of bottom barriers or diver pulling could maintain boat paths, docks and swimming areas with no risk to public health. 

Paddlers on Lake Pend Oreille. Courtesy photo.

Upon returning to the work of protecting North Idaho’s great lakes after a decade out of the area, last summer I again received phone calls from community members concerned about herbicide application. Flyers had been posted on docks and shorelines indicating that chemicals would be applied to the water in order to kill these same weeds. Both ISDA and the U.S. Army Corps of Engineers had resumed herbicide use in their efforts to manage aquatic invasive species in the lake. 

We met with the agencies last year and discussed the concerns that we had heard. We were assured there would be a collaborative process with opportunities for public input as plans were developed for the summer of 2024. Then, at a public meeting earlier this month, the agencies gave presentations to a largely empty room. It was in stark contrast to the level of interest our community has expressed, and we were disappointed we weren’t notified about the meeting in time to help get the word out. 

At the meeting, ISDA laid out its plans to conduct a eurasian watermilfoil survey, likely in mid-July, when the plants reach at least three feet. The survey will include the entire lake area near the shoreline that is not managed by the Corps. For areas they target with chemical application, they expect to begin in early August. Notices will be posted on docks 24 hours before chemicals are applied, and after 14-day notices have been given to those who are registered water rights holders within 1/4 mile of the areas to be treated. Municipal water suppliers within a “reasonable distance” will also be given notice.

We are pleased to be assured that City Beach and Sand Creek in Sandpoint continue to be treated by ISDA for flowering rush with mechanical removal, and that the agreement with the city of Sandpoint to avoid chemicals in the high-use swim area persists. ISDA has no plans to chemically treat submerged flowering rush this year. 

You can learn more about ISDA’s plan as they develop it, at: invasivespecies.idaho.gov/treatment-plans.

The Corps manages limited acreage in the Pend Oreille system, and their herbicide use will target only flowering rush. They will conduct a survey in late July to determine chemical application areas. The Corps is tentatively planning to treat 28 acres in August. 

Protections for bull trout, which are listed as threatened under the Endangered Species Act, restrict the timeframe of chemical herbicide application to July 15 through Aug. 31. 

Although this process may be more protective of people and special places than in years past, with chemicals applied to much smaller areas than previously, there is still room for improvement. As a voice for clean water and protector of the great lakes of North Idaho, the Idaho Conservation League hopes to work with the agencies to:

• discontinue use of the most toxic chemicals;

• ensure that drinking water intakes and public beaches are avoided;

• reduce the acreage of chemical application;

• urge agencies to focus on control methods other than chemicals, including bottom barriers and mechanical removal, where appropriate;

• develop a system where shoreline homeowners can “opt out” of chemical herbicides, similar to the system used on roadways;

• ensure the public is informed and has robust opportunities to voice concerns prior to chemical applications.

North Idaho’s lakes are scenic wonders, priceless economic assets and the foundation of our way of life. We must leave these waters better than we found them, so we can enjoy them for generations to come. 

For more information about aquatic invasive species plans for this summer, contact:

Idaho State Department of Agriculture, Jeremey Varley, [email protected] or 208-993-0950; U.S. Army Corps of Engineers, Taylor Johnson, [email protected] or Andrew Huddleston, [email protected]. Both can be reached at 208-437-3133.

Jennifer Ekstrom is North Idaho director for the Idaho Conservation League.