Protecting Washington’s waters
Invasive freshwater mussels threaten our waters, economy, and infrastructure.
Washington remains one of the few western states without established populations of highly invasive freshwater mussels including quagga, zebra, and golden mussels, but the regional risk of introduction continues to increase. Invasive freshwater mussel populations in Idaho and California, as well as interceptions and a detection in Oregon, demonstrate the threat is closer than ever before.
Invasive freshwater mussels pose an imminent threat to Washington’s economy, freshwater resources, environment, public health, and way of life. Where introduced, eradication is rarely possible, leading to irreversible environmental impacts and ongoing mitigation and management costs impacting all Washingtonians and industries.
An imminent threat to Washington
Invasive freshwater mussels, an aquatic invasive species (AIS), are not currently known to be established in Washington. However, recent interceptions at Washington’s mandatory watercraft inspection stations and in nearby states and regional invasive freshwater mussel detections illustrate that prevention efforts are more critical than ever before.
The Columbia River Basin, Puget Sound Basin, and other waters support approximately eight million people, irrigate more than 670,000 acres, facilitate more than $25 billion in annual commerce, and generate one-third of hydropower in the Pacific Northwest. They also sustain fisheries, provide drinking water and recreation opportunities, and support tribal treaty-protected resources.
If established, mitigation costs to hydroelectric facilities alone are projected to exceed $100 million annually, with similar costs anticipated for agricultural irrigation, drinking and wastewater systems, fish hatcheries and fish passage infrastructure, navigational locks, and other sectors using untreated environmental water known as raw water. Invasive freshwater mussels can attach to infrastructure, plants, and native species, a process known as fouling. In Brazil, golden mussels fouling in hydroelectric facilitates account for more than $100 million in lost power production due to outages annually.
Quagga and zebra mussels were introduced to the United States in the 1980s through the ballast water of trans-oceanic ships and have since spread westward across North America. Invasive freshwater mussels can spread through connected waterways and into unconnected waterways through human activity. Adult mussels, typically measuring an inch or less, and microscopic juveniles can hitch a ride overland on aquatic equipment, gear, and watercraft to new, uninfested areas.
Accidental human spread likely contributed to the introduction of quagga mussels in the Snake River in south-central Idaho, first detected in 2023. In 2024, golden mussels were detected in the U.S. for the first time near the Port of Stockton, California. Believed to have come to the U.S. in the contaminated ballast water or hulls of trans-oceanic ships, much like quagga and zebra mussels, golden mussel detections have since spread as far south as Los Angeles. Within two years, golden mussels have been impactful to the point multiple counties have declared emergency proclamations and spent millions to mitigate impacts, with a county estimating more than $36 million will be required annually.
While golden mussel detections appear to be spreading south, the interception of a golden mussel-fouled watercraft in Oregon in early 2026, and two additional interceptions on Interstate 5 in summer 2026, demonstrates an active pathway for northward spread. Due to the potential for golden mussel introduction, Washington is undertaking permanent rulemaking to prohibit possession of the species. When a single, dead quagga mussel was detected at Oregon’s Prineville Reservoir approximately 177 river-miles from the Columbia River Basin, it became clear the threat of introduction continues to move closer to Washington’s borders.
Investing in prevention and readiness
The state Legislature’s crucial investment in prevention and readiness efforts during the 2025–2027 biennium enabled WDFW, working with tribal governments and federal, state, regional, and local partners, to significantly expand and strengthen statewide watercraft inspection and decontamination, early detection monitoring, rapid response planning, public outreach, scientific assessment, and interagency coordination.
This investment leveraged 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. During the 2025–2027 biennium the APC-WID program required a 50% cost share of non-federal funds, meaning the program matched every dollar the state invested in invasive freshwater mussel prevention and readiness, effectively doubling available funding.
Prevention is an investment in the future
As the risk of introduction and establishment grows, so does the importance of prevention. If established, invasive freshwater mussels are anticipated to have far-reaching impacts beyond the waterbody they are introduced.
Hydropower, municipal water systems, and irrigation all rely on water intake pipes that can be clogged by invasive mussels leading to reduced efficiency and higher management and mitigation costs likely passed on to ratepayers and consumers. Three-fourths of Washington’s agricultural output relies on irrigation, contributing $9.6 billion to the economy annually. Impacts on irrigation systems can affect yields and production costs, leading to rising prices and worsening food insecurity.
Navigation and port infrastructure fouled by invasive mussels is anticipated to impact shipping times and costs as mitigation and management costs rise. In the Columbia River Basin alone, $31.5 billion in commodities and products are at risk if invasive freshwater mussels become established. The Columbia River Basin is a key U.S. trade gateway leading the nation in wheat exports and coming in second as a pathway for exporting soy and corn. Rising shipping costs are likely to be passed on to consumers, potentially compounding the impacts of increased food insecurity.
Environmental impacts of freshwater invasive mussel establishment extend beyond the native species and people using the infested waterbody. Irreversible changes to critical habitat negatively impact native species populations and reduce available habitat for species like salmon. Outdoor recreation and fisheries contribute $20.5 billion to the state’s economy annually, economic activity significant to many local economies and Washington families. Decreasing salmon populations due to habitat loss can have broader implications on Southern Resident Killer whale population which rely on Chinook Salmon for food. Establishment also threatened billions of dollars invested in salmon recovery, fish passage, culvert replacement, and hatchery modernization.
Impacts from establishment also threaten human health. In addition to increases in food insecurity, invasive freshwater mussels have also been shown to lead to an increase in botulism causing bacteria, a serious neurotoxin, and increases in harmful cyanobacteria leading to harmful algal blooms.
Once established, eradication of invasive freshwater mussels can be nearly impossible, leading to long-term economic impacts. Increased management and mitigation costs, retrofits, and decreased efficiency are likely to lead to permanent cost increase for industries, communities, ratepayers, and taxpayers.
The impacts of establishment are anticipated to disproportionately impact vulnerable communities and populations who depend on healthy, functioning aquatic ecosystems and reliable water infrastructure. Rural communities, agricultural producers, irrigators, commercial and recreational fisheries, and communities throughout the Columbia River Basin, Puget Sound are particularly at risk.
Investing in prevention avoids long-term economic and environmental impacts. Watercraft inspection and decontamination stop the introduction of invasive freshwater mussels, early detection and monitoring identify potential introductions before establishment, and rapid response preparedness allows WDFW and partners to react quickly should mussels be detected. Prevention requires everyone’s participation, and investing in public outreach helps increase awareness of and compliance with preventative actions to stop the spread. Additionally, federal partnerships and funding expand WDFW and partner’s prevention and readiness capacity significantly.
Coordination and long-term leadership and planning
Successful prevention of the spread of invasive freshwater mussels and response readiness requires collaboration across jurisdictions within Washington state and the greater Pacific Northwest region. The 2025–2027 Legislative investment enabled WDFW to engage state, tribal, federal, regional, and local entities to develop rapid response plans and near-term action recommendations.
Should invasive freshwater mussels be detected in Washington state, WDFW and partners are prepared to act thanks to this rapid response planning. 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.
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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.
While golden mussels pose similar threats as quagga and zebra mussels and can be spread between waterbodies through many of the same pathways, they also present unique challenges. Golden mussels can tolerate higher salinity for short periods of time than other invasive freshwater mussels, allowing them to survive in ports where other freshwater mussels can’t. Additionally, golden mussels require significantly less calcium in waters, required to grow and develop shells, meaning they are able to survive and reproduce in waterbodies that aren’t conducive for quagga and zebra mussels.
They can also spread via contaminated ballast water from trans-oceanic ships or those traveling to Washington from infested areas like California. In 2025, 1,097 vessels discharged 14 metric tons of ballast water, averaging 12,762 metric tons (3.37 million gallons) per vessel. By comparison, a wakeboard boat’s ballast tank may retain an average of around 8 gallons of water. Additionally, hull-fouling, adult golden mussels capable of breeding attaching to the underside of ships, could also pose a threat for ships traveling from California. Preliminary federal research simulating oceanic conditions indicated that golden mussels on the hulls of oceangoing vessels were likely to survive the voyage from the San Juaquin delta in California to Columbia and Snake River System freshwater ports.
Prevention is a collective effort
Decades of prevention efforts throughout the state and nationally in the U.S. and Canada have slowed the westward spread of invasive freshwater mussels, but successful prevention requires everyone’s participation. Even though overland transport on contaminated aquatic equipment, gear, motorized and non-motorized watercraft is preventable, spread due to human activity remains a major pathway.
Anyone who works or recreates on or in the water can help stop the spread by practicing Clean, Drain, Dry but research shows improved public outreach and education around preventative actions is needed. The Legislature’s 2025–2027 investment enabled WDFW to develop and implement a statewide, strategic communications and outreach program to raise awareness, engage the public, and foster behavioral change in support of prevention efforts.
Watercraft inspection and decontamination
Practicing Clean, Drain, Dry is important to preventing the accidental transportation of invasive freshwater mussels, but with microscopic larvae and adults measuring less than an inch, hitchhiking mussels can be easy to miss. Stopping at mandatory watercraft inspection and decontamination stations is key to preventing their introduction.
Inspectors are trained to look for hidden AIS and provide free decontaminations to any watercraft at risk of transporting AIS including invasive freshwater mussels. At some stations, an invasive freshwater mussel detection dog assists with inspections to find mussels that are difficult to locate visually.
Thanks to the Legislature’s 2025–2027 investment, watercraft inspection and decontamination operational capacity increased in 2024. In fiscal year 2025 (July 1, 2025, to June 30, 2026), inspectors performed 10,795 more inspections, a 19% increase, than the previous year and performed 1,524 more decontaminations, a 64% increase. Inspectors also intercepted 1,446 more watercraft contaminated with AIS, an increase of 60%, before they could launch Washington’s waters. In both fiscal years 17 watercraft contaminated with quagga and/or zebra mussels were intercepted (Table 1). Golden mussels have not been detected or intercepted in Washington state.
We will feature a closer look watercraft inspectors’ work throughout the state in a blog on Wednesday.
Monitoring and preparing for rapid response and containment
Invasive freshwater mussels are nearly impossible to eradicate once established. Early detection is critical to prevent establishment and spread beyond the initial introduction area. As a result of a 2025–2027 Legislative investment, WDFW was able to collect more samples at waterbodies statewide using a variety of methods than in previous years. Monitoring teams detected no invasive mussels statewide.
During this period, staff collected 9,241 samples and surveys statewide, a 48% increase over the previous state fiscal year. Monitoring teams also took 2,035 water quality measurements, a 26% increase over the previous year (Table 2).
Due to the establishment of quagga mussels in Idaho, early detection efforts were increased in Washington’s Snake and Middle Columbia Rivers to identify potential downstream introductions. In total, WDFW monitored 222 waterbodies statewide at 428 sites — including 6,232 samples.
Take a closer look at WDFW’s monitoring teams and early detection in our Friday blog.
Infrastructure risks
Threads from invasive freshwater mussels are a major concern for all raw water infrastructures, including WDFW’s dozens of fish hatcheries. To better understand hatchery vulnerability, WDFW with assistance from the U.S. Geological Survey developed and piloted a fish hatchery vulnerability assessment. In the future, WDFW plans to work with other raw water industries at risk such as managers at non-WDFW fish hatcheries, utilities, and irrigators to share procedures and assist with increasing overall raw water vulnerability assessments.
Prevention protects Washington’s waters and Washingtonians
By investing in prevention and readiness efforts in the 2025–2027 biennium, the Legislature enabled WDFW and partners to strengthen and expand efforts to protect our freshwater resources, economy, public health, energy reliability, agriculture and food security, outdoor recreation and tourism, fish and wildlife resources, and shipping.
We still have time to protect Washington’s waters and Washingtonians from the threats posed by invasive freshwater mussels. While WDFW and partners work to protect our waters statewide, anyone who recreates or works on the water can help stop the spread of AIS. Visit our website to learn more about how you can help Protect Our Waters.
