Protecting Washington’s Waters: Prevention and Readiness Against Invasive Mussels
Quagga and zebra mussels (QZM), aquatic invasive species (AIS), pose an imminent threat to Washington’s environment, economy, health, and way of life. Though not currently known to be in Washington, recent detections of quagga mussels (QM) in the Snake River in south-central Idaho in September 2023 and October 2024 demonstrate the significant risk that they will be introduced to our waters.
First discovered in the Great Lakes in the 1980’s, QZM were likely introduced via ballast water from trans-oceanic ships. Usually measuring an inch or less, these relatively small freshwater mussels spread from the Great Lakes to connected waterways but managed to travel to unconnected waterbodies by hitching a ride overland on aquatic equipment, gear, and watercraft — motorized and non-motorized. Though largely preventable, overland transportation of QZM and other species of AIS remains a major pathway of introduction. Practicing clean, drain, dry; watercraft inspection; and decontamination are all methods to stop the spread of invasive mussels but require behavioral change from aquatic recreationists and workers.
Where introduced, QZM are nearly impossible to eradicate thanks to their ability to rapidly reproduce and attach to surfaces. A single mussel can produce over 1 million eggs per year and free-floating larvae are microscopic — making them impossible to detect visually. Adults have long rope-like threads called byssal threads that attach to surfaces including rocks, plants, and even other species of mussels as well as infrastructure.
Reaching densities of up to tens of thousands per individual square meter, these invasive mussels can severely damage habitats and threaten native fish and wildlife resources. Additionally, byssal threads allow them to colonize intake pipes, threatening hydropower systems, irrigated agriculture, locks, fish ladders, hatcheries and utilities like drinking water. Should QZM establish in Washington, long-term mitigation and management costs are anticipated to exceed $100 million annually.
The environmental and economic threats posed by quagga mussels prompted strong support for prevention and readiness actions from the Washington State Legislature and, thanks to sponsorship by Representative Mary Dye and support of other legislators, $1.81 million was appropriated from the General Fund in state fiscal year 2025 (SFY25), starting in July 2024 and ending in June 2025. This investment qualified WDFW for an additional $1.81 million in funding from the U.S. Army Corps of Engineer’s Aquatic Plant Control (APC) Watercraft Inspection and Decontamination (WID) cost-share program which requires a 50% cost-share of non-federal funds.
These funds supported coordination with state, tribal, federal, regional, and local entities; increased watercraft inspection and decontamination; addressing introduction pathways; monitoring and preparing for rapid response and containment; understanding the risk to infrastructure; and public outreach.
Coordination and long-term leadership and planning
Successful prevention of the spread of QZM and response readiness requires collaboration across jurisdictions within Washington state and the greater Pacific Northwest region. WDFW engaged with state, tribal, federal, regional, and local entities to develop invasive mussel rapid response plans and near-term action recommendations.
Should QZM be detected in Washington State, WDFW and partners are prepared to act thanks to rapid response planning in SFY25. The State of Washington Interagency Zebra and Quagga Mussel Rapid Response Plan outlines response procedures and, in response to the detection of quagga mussels in the Snake River, the Interagency Quagga and Zebra Mussel Rapid and Extended Response Plan for the Snake River in Washington State was developed to specifically address detections in the Snake River.
Like Washington, Oregon is not currently known to have established populations of QZM and faces the same imminent threats. Forming the Oregon and Washington Invasive Mussel Near-Term Action Working Group, WDFW and the Oregon Department of Fish and Wildlife collaborated with partners and entities from both states and the federal government to release Near-Term Action Recommendations for preventing the spread of QZM and detection and rapid response readiness and preparedness.
The Quagga and Zebra Mussel Tribal Policy Coordination Group brought together co-managers and tribes from the Upper Columbia and Columbia River, to spotlight the risk and gather feedback for WDFW’s approach to increasing prevention and readiness. Coordination between WDFW and tribes is key for the success of prevention and readiness actions. Additionally, tribal governments have promoted the 2025 Affiliated Tribes of Northwest Indians resolution calling on Congress to appropriate $8 million to the U.S. Bureau of Indian Affairs for Northwestern regional invasive species grants. WDFW also provided information and technical support to numerous tribes, including participating in the 2025 Affiliated Tribes of Northwest Indians Natural Resources Summit, co-presenting with the Nez Perce Tribe; and provided the Kalispel Tribe of Indians a capacity building grant as seed funding to begin early detection monitoring.
Increased watercraft inspection and decontamination
Overland transport of QZM and other AIS on contaminated aquatic equipment, gear, and motorized and non-motorized watercraft is preventable. Mandatory watercraft inspection and decontamination stations are key to protecting our waters from QZM.
Inspections are performed on all watercraft, but decontaminations are only preformed on watercraft at risk of transporting QZM or other AIS. This includes watercraft found to be contaminated with QZM or other AIS, watercraft last used in waterbodies known to be contaminated with QZM, or watercraft that inspectors can see has not been cleaned, drained, and dried. Inspectors look for AIS and provide free decontamination services for at-risk watercraft. At some stations, a QZM detection dog assists with inspections. Mussel detection dogs are trained to identify only the presence of quagga and zebra mussels which can be difficult to locate visually.
The Clarkston station protects Washington from potentially contaminated watercraft entering Southeast Washington. Thanks to funding provided the legislature in SFY25, watercraft inspections increased 87% from the previous year (Table 1). Invasive mussel detection canine, Fin, assisted Clarkston staff with inspections 83 times in 2025, an increase of 4050% from 2024’s two inspections. Decontaminations also increased at Clarkston to 17 in SFY25, indicating that watercraft at-risk of transporting QZM or other AIS are traveling into the state from the Southeast.
In South Central Washington, the Pasco station also saw an increase in inspections of 8% from the previous year with decontaminations of at-risk watercraft increasing 82% from the previous year (Table 2). Additionally, the Pasco station intercepted watercraft fouled with invasive mussels during SFY25.
Increased watercraft inspection and decontamination capacity strengthens prevention efforts. While WDFW focuses on major watercraft transportation routes, the agency is also training and collaborating with other entities and partners. WDFW sponsored Watercraft Inspection and Decontamination Level 1 and 2 training for tribes, utilities, and other partners in June of SFY25.
Addressing introduction pathways
While prevention efforts often focus on major pathways of spread like contaminated watercraft, the importance of addressing alternate pathways of introduction became apparent in 2021 when invasive mussels were detected on Marimo moss balls shipped to pet stores in Washington. Contaminated Marimo moss balls were detected again in 2024 in Renton, thanks to an aware fish wholesaler who alerted WDFW.
Thanks to SFY25 prevention and readiness funding, a WDFW AIS early detection monitoring team was able to arrive within minutes to collect samples of the mussels, moss balls, and eDNA, as well as plankton tows. To assist with future compliance inspection and rapid response, WDFW has obtained a list of retail pet stores from the Department of Licensing and is planning future outreach to pet stores and the public in partnership with the Washington State Department of Agriculture and the Washington Invasive Species Council.
Fish stocking and transport permits protect our native fish species from diseases and pathogens and ensure that fish will not harm species or habitat. Some fish are imported to Washington from out-of-state, or other countries where aquatic invasive species such as quagga or zebra mussels are present. WDFW now requires documentation from fish hatcheries showing invasive species inspections and results alongside fish health information, to ensure that transported or stocked fish don’t introduce invasive mussels or other problems into our waters.
Monitoring and preparing for rapid response and containment
Identifying infestation early is critical to preventing QZM from establishing populations and spreading beyond the area of initial introduction. Additional SFY25 funding allowed WDFW monitoring teams to increase monitoring efforts, using multiple methods to collect more samples at waterbodies statewide than in previous years. Due to the recent detection of QMs in Idaho, monitoring and early detection efforts were intensified in Washington’s Snake and Middle Columbia rivers to detect downstream establishment. WDFW increased early detection monitoring frequency and sites on the Snake River, where the river enters Washington state to the confluence with the Columbia River at the Tri-Cities. A total of 1,853 sampling instances occurred at 36 sites on the Snake River. In total, WDFW monitored 222 waterbodies statewide at 428 sites — including 6,232 samples. No QZM were detected in Washington’s waters.
In addition to the development of the State of Washington Interagency Zebra and Quagga Mussel Rapid Response Plan and Interagency Quagga and Zebra Mussel Rapid and Extended Response Plan for the Snake River in Washington State, WDFW and the U.S. Geological Service (USGS) partnered to initiate a State of Washington Dreissenid Risk Assessment still in development. WDFW is using this information to bolster response preparedness by purchasing supplies and equipment, staging it for future practice and use.
Understanding the risk to infrastructure
With the ability to attach to surfaces and foul intake pipes, QZM pose major concerns to any raw water infrastructure, such as WDFW’s dozens of fish hatcheries. Microscopic, free-floating larvae can enter hatcheries through contaminated natural water sources or be hiding in water used to transport live fish. To better understand hatchery vulnerability, WDFW with assistance from the U.S. Geological Survey has developed a hatchery vulnerability assessment. Currently, staff are pilot surveying five hatcheries to refine and finalize assessment procedures. In the future, WDFW will work with utilities, irrigators, and other raw water industries at risk to share procedures and assist with increasing overall raw water vulnerability assessments.
To better understand the risks associated with raw water systems and to explore engineering solutions, WDFW requested and took part in a Pacific States Marine Fisheries Commission 100th Meridian Initiative Columbia River Basin Team raw water infrastructure working group. Products of this working group include Invasive Mussel Control at Hydropower Facilities: An Update report, and Survey on Invasive Mussel Risks to Hydropower & Raw Water Infrastructure, and a survey of national and international raw water providers to understand their readiness, costs, successes and failures as lessons learned to inform future effort if the worst were to happen in Washington.
WDFW is also engaging with other jurisdictions and stakeholders on prevention and preparedness efforts such as the Preparing for Invasive Mussels: Vulnerability Assessment Guide for Raw Water Infrastructure and touring the Pacific Northwest National Labs to better understand lab capabilities and opportunities to bolster research.
Public Outreach
Preventing the spread of QZM to Washington’s waters requires a collective effort that includes the members of public. Practicing clean, drain, dry; stopping at watercraft inspection stations; and decontaminating at-risk aquatic equipment, gear, and watercraft is essential to protecting our waters, but some residents and visitors aren’t aware prevention starts with them. To help raise awareness, engage the public, and foster behavioral change in support of prevention efforts, WDFW acquired an aquatic invasive species communications specialist to develop and implement a statewide, strategic communications and outreach plan for QZM in SFY25.
Outreach materials developed as part of this strategic plan include an informational QZM rack card and a Clean, Drain, Dry brochure. Recognizing the importance of reaching everyone who recreates or works in or on the water, the rack card and brochure are available upon request in 9 languages including English, Chinese, Hindi, Korean, Russian, Ukrainian, Vietnamese, Tagalog, and Spanish. Digital outreach including social media content, blog posts in English and Spanish, and a webinar in collaboration with the Washington Invasive Species Council were also developed and implemented. As part of improving digital outreach, WDFW also worked to update existing and create new pages on the Agency’s website to improve public outreach.
In addition to statewide messaging, watercraft inspection station staff preform outreach and education during inspections, preforming 55,866 watercraft inspections in SFY25. WDFW staff also participated in 17 outreach events and opportunities including conferences, meetings, and workshops and canine detection dog, Fin, participated in 4 events with his handler, Nick Knauss.
Protecting our waters now and in the future
For decades, Washington has successfully prevented the introduction and establishment of invasive mussels thanks to efforts throughout the state and nationally in the U.S. and Canada. Detection of quagga mussels in the Snake River in Idaho was a wake-up call for jurisdictions to increase prevention efforts and response readiness.
Answering that call, WDFW, co-managers, tribes, researchers, industry, and federal, state and local governments have taken decisive and comprehensive action with support from the Washington State Legislature in SFY25. Investments made in prevention and response readiness supported coordination with state, tribal, federal, regional, and local entities; increased watercraft inspection and decontamination; addressing introduction pathways; monitoring and preparing for rapid response and containment; understanding the risk to infrastructure; and public outreach.
With support from the state legislature in SFY 2026 and 2027, WDFW will continue increased invasive mussel prevention and response readiness efforts, building upon statewide SFY25 accomplishments. WDFW can’t do it alone, though. Collective efforts to prevent the introduction and establishment of QZM and other AIS are critical and anyone who recreates or works on or in the water can help.
Any time you go out on the water, remember to clean, drain, and dry all your aquatic equipment, gear and watercraft — both motorized and non-motorized. It’s illegal to transport aquatic invasive species from one waterbody to another in the state and practicing clean, drain, dry every time you leave the water ensures you won’t receive fines up to $5,000 or a year in jail. With your help, Washington can protect our waters from invasive mussels.
Updated 9/18/2025: The original version of this blog contained 2 errors in the Clarkston Station percentage increases that have been corrected.
