North Idaho’s lakes deserve safer solutions, not chemicals
August 2, 2025
By Jennifer Ekstrom Reader Contributor
Our North Idaho lakes are havens for our communities. They are lifelines for fish and wildlife, cherished places for family excursions and vital sources of clean drinking water. Our treasured lakes deserve protection that prioritizes both human health and ecological integrity.
Once again this summer, Lake Pend Oreille and Cocolalla Lake are targeted for chemical herbicide application to kill Eurasian watermilfoil and flowering rush, which are aquatic invasive weeds. These weeds can certainly cause a nuisance for boating and swimming, but thankfully the areas where the nuisance is greatest are well suited for diver pulling to remove the weeds.
The Idaho State Department of Agriculture is finishing its weed surveys on Lake Pend Oreille, and is developing plans to kill Eurasian watermilfoil shortly thereafter. These plans will include using both chemical herbicides and diver pulling. Once the plans are developed, residents with formal water rights will receive a 14-day notice before herbicide application, and other waterfront homeowners may get just a 24-hour dockside notice, leaving many unaware.
The plans for Cocolalla Lake are already completed, with many areas of weeds slated for diver pulling. There are just fewer than 10 acres of weeds in Cocolalla Lake that will be targeted with the chemical herbicide florpyrauxifen-benzyl (ProcellaCOR).
Aquatic weeds washed up on the shoreline at the Memorial Field boat launch. If these weeds were pulled by divers they would be removed from the water, protecting water quality and the aesthetics of our shorelines. Courtesy photo.
To stay updated about ISDA’s 2025 weed surveys, chemical application and diver pulling plans, check the map at invasivespecies.idaho.gov/treatment-plans.
Meanwhile, the U.S. Army Corps of Engineers has announced plans to apply diquat dibromide (Reward) and diquat dibromide plus endothall (Aquastrike) to up to 60 acres of submerged flowering rush at Riley Creek, Morton Slough, Oden Bay North and the Pack River Delta. This is planned for Monday, Aug. 4-Friday, Aug. 8. The Corps is not recommending fishing or swimming restrictions; however, it is recommended that animals should not consume the water for 24 hours. Humans should not drink the water nor irrigate the landscape for three days, and there is a five-day restriction on irrigating food crops.
The Corps will avoid applying the herbicide within 600 feet of public drinking water intakes and water rights holder intakes.
Chemical use raises serious concerns, in addition to human exposure. When large quantities of weeds decompose all at once, they release nutrients that can fuel the next generation of weeds, increase the risk of toxic algae outbreaks and deplete oxygen that fish need to survive. This risk is elevated when they are killed at the height of summer when temperatures are high.
Concerns about human exposure and aquatic life increase because of a loophole in the permitting process that allows for duplicative applications — this can result in concentrations that exceed approved thresholds indicated on the product labels.
The Idaho Department of Environmental Quality needs to update its Pesticide General Permit, and fix a critical loophole that allows herbicide discharges on areas up to 80 acres — 60 football fields — with no coordination or meaningful regulation. As a result, multiple overlapping herbicide applications could occur by ISDA, the Corps, homeowners associations and individuals.
We all want to reduce the spread of invasive aquatic weeds, but chemical herbicides should be a last resort, not the first line of defense.
The most effective, environmentally safe methods for controlling invasive weeds in the areas where they are truly a nuisance — like boat launches and swimming areas — are diver hand-pulling and bottom barriers. These techniques work, and they don’t contaminate water, increase nutrient pollution or harm fish.
Join the Idaho Conservation League in sending a strong message before the plans are finalized and implemented. Urge ISDA and the Corps to reduce or cancel herbicide applications and focus on safer, proven alternatives. Contact the following people to make your voice heard:
Chanel Tewalt; director, ISDA; [email protected]; 208-332-8503; Jeremy Varley; chief treatment engineer and Noxious Weeds Section manager, ISDA; [email protected]; 208-332-8667; Taylor Johnson; chief, Natural Resources, U.S. Army Corps of Engineers; 208-437-3133 ext. 7225; [email protected].
Share your own story with them, and consider including some of these key points: avoid chemical applications near drinking water intakes by a wider safety margin; cancel or minimize the acreage of herbicide application; and prioritize non-toxic, effective methods — diver pulling and bottom barriers
Jennifer Ekstrom is North Idaho director of the Idaho Conservation League.
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