Invasive Species & Herbicides

Eurasian Watermilfoil, Curly-Leaf Pondweed, Flowering Rush, Zebra Mussels and Quagga Mussels

Lake Pend Oreille | Pend Oreille River

Limited herbicide treatment of aquatic invasive weeds

We advocate for limited use of herbicides to control aquatic invasive and nuisance weeds and are working to establish a comprehensive, ecologically sound, non-toxic approach to long-term management of vegetation in our waterways.

We worked closely with the City of Sandpoint in 2012 to establish and implement a new management program for aquatic invasive weeds at City Beach and the Windbag Marina using diver assisted hand-pulling. This program focuses on eliminating the need for chemical applications in our high-use swimming and recreational areas.

In addition, we support the use of biological control, which is the use of naturally occurring predators or pathogens to manage populations of aquatic invasive and nuisance weeds – including Eurasian Watermilfoil.

Through legislative action in the winter of 2015, our team’s efforts successfully changed Idaho’s Noxious Weed Law to allow for the movement of aquatic invasive weeds for the purposes of biological control research and implementation. With such a change, we hope to stimulate research into biological control agents and collaborate on their implementation as an additional tool to help safely manage the aquatic invasive weed populations in our watershed.

In February 2020, the City of Sandpoint announced a 3 year contract with a local weed management company which will guarantee the use herbicide-free solutions to beat back aquatic invasive species in areas frequented by swimmers and boaters on Lake Pend Oreille, including diver-assisted suction harvesting, bottom barriers, and other recommended methods. We plan to continue advocating for safe management practices and would like to thank the City of Sandpoint for its effort to keep our swimming areas free of aquatic herbicides! 


Did you know?

Our team worked closely with the City of Sandpoint in 2012 to establish and implement a new management program for aquatic invasive weeds at City Beach and the Windbag Marina using diver assisted hand-pulling.

Invasion and spread of new aquatic invasive species

Certain invasive species can seriously threaten the stability of the aquatic ecosystem in addition to degrading water quality. Our team works to prevent the introduction and spread of new aquatic invasive species, such as zebra mussels, quagga mussels, curly-leaf pondweed, Eurasian Watermilfoil, and flowering rush, within the Lake Pend Oreille system by raising community awareness and distributing educational materials to the public. 

Eurasian Watermilfoil

About: Eurasian watermilfoil is a rooted, submerged aquatic plant that can grow up to 20 feet tall. This plant is native to Europe, Asia, and North Africa and was likely introduced to the United States through the movement of watercraft and water-related equipment, such as in the ballast of a ship.

Threats: Eurasian watermilfoil spreads easily and grows quickly thanks to its ability to self-fragment, where pieces of milfoil break off and re-root nearby. Eurasian watermilfoil often creates a dense mat at the water’s surface which can become tangled in boat propellers and hindering water recreation. It also crowds out native plants, reduces biodiversity, diminishes fish habitat, and negatively impacts wetland habitats.

Sustainable Control Methods: Eurasian watermilfoil can be mechanically controlled with cutting and pulling by hand or with equipment and by using benthic mats. Biological control using weevils is also being researched and utilized in the US.

Curly-Leaf Pondweed

About: Curly-leaf pondweed is a rooted, submerged aquatic plant that can tolerate extreme conditions. It is native to Eurasia, Africa, and Australia and was likely spread by migrating waterfowl, intentional planting, and watercraft transportation.

Threats: Curly-leaf pondweed forms dense mats in the water, which then creates a great deal of waste when it dies off. Summer die-back can reduce dissolved oxygen levels and spark algae blooms. Large mats of it can inhibit aquatic recreation and outcompete native plants for light and space early in the growing season.

Sustainable Control Methods: Curly-leaf pondweed can be mechanically controlled through raking or seining it. Biological control using grass carp is currently being used in the US. 

Flowering Rush

About: Flowering rush is a reed-like aquatic plant with pink flowers that oftens grows in shallow, slow-moving water. It can also grow in deeper water in a submerged form that does not produce flowers. Flowering rush is native to Europe and Western Asia and was likely introduced the cargo ship ballast water and through international garden trade. It can easily be spread through water transport or by wildlife. 

Threats: Flowering rush creates dense growths along shorelines and wetlands, making it difficult to access open water. It can also outcompete native plants for habitat, threaten biodiversity, and decrease suitable habitat for native animals.

Sustainable Control Methods: Flowering rush can be mechanically controlled by cutting and hand digging. Raking or pulling can disturb the root system and is therefore not recommended. 

Zebra Mussels & Quagga Mussels

About: Zebra mussels and quagga mussels are aquatic invasive mussel species that can colonize soft and hard surfaces. They are native to eastern Europe and were introduced to the US through ballast water discharge from cargo ships. They can easily spread by attaching to watercraft, aquatic plants, docks, and other equipment and can survive out of water for up to 30 days. 

Threats: Zebra mussels and quagga mussels pose great ecological and economical threats throughout the US. They can reduce food available for other aquatic organisms, disrupt food webs, facilitate toxic algal blooms, threaten habitats for native species, and clog water infrastructure. They easily encrust lake and river bottoms as well as docks and watercraft, threatening aquatic ecosystems and recreation.

Sustainable Control Methods: Zebra mussels and quagga mussels invasions can be physically managed with benthic mats, water drawdowns to dry them out, or manual removal. Biological control treatments being researched involve the introduction of redear sunfish and the addition of carbon dioxide into the water column.

What you can do: Clean – Drain – Dry

In order to stop the spread of spread of aquatic invasive species, we all need to work together to protect our natural resources and be responsible for our actions! In every water body, every time, make sure to clean, drain, and dry your aquatic recreational equipment and all your gear.


 Clean off all visible aquatic plants, animals, and mud before leaving the water. Rinse equipment inside and out. Rinsing with water will remove organisms, but using hot water is preferred since it will kill the organisms. This is remove visible and large-bodied organisms that may have attached to recreational equipment during use.


Drain motor, bilge, livewell, and other water containing devices before leaving the water. This will remove small or invisible organisms that may have potentially entered water containing devices.


Dry everything for at least five days or wipe down your equipment with a towel. This will help prevent the spread of organisms that can survive in standing water.

 – Always report new sightings if you think you have found an invasive species to local authorities! –


Stop Aquatic Hitchhikers!
Information about aquatic invasive species and what you can do to prevent them from spreading.

Invasive Species in Idaho
Website about invasive species specific to Idaho, including Idaho laws and rules regarding invasive species and noxious weeds.

Bonner County, ID – Noxious Weeds Department
Contact information for the local weeds manager in Bonner County and additional resources about our local weeds and programs.

Support this Program!

Support healthy, chemical-free recreational areas and help our local community expand its program for non-chemical management of aquatic noxious weeds.

Become a Citizen Scientist!

Become a trained citizen scientist. Collecting water samples is a great way to enjoy time on the water & get involved in active stewardship of our local waterways!