Golden mussels prohibited in Washington after Oregon interception
Recent interception confirms an active pathway for northward spread and an imminent threat to Washington.
In early April, Oregon Department of Fish and Wildlife (ODFW) confirmed the interception of a watercraft fouled with golden mussels (Limnoperna fortunei) at the Ashland Boat Inspection Station on Interstate 5 Northbound. The vessel was traveling from California’s Sacramento-San Joaquin Delta where the invasive mussels were first discovered in North America in 2024.
Since 2024, golden mussels have spread south of the Sacramento-San Joaquin Delta, but the Oregon interception confirms an active pathway north for golden mussels through movement of contaminated recreational boating and aquatic equipment. No longer a distant threat, the risk that golden mussels could be introduced to our waters is significant.
Where introduced, these invasive freshwater mussels destroy native habitats and threaten fish and wildlife species. They can clog water intake pipes impacting critical infrastructure necessary for hydroelectric power systems, irrigated agriculture, drinking water, and sewage costing utilities, companies, and taxpayers millions of dollars in mitigation and management costs.
To protect our waters, the Washington Department of Fish and Wildlife (WDFW) has enacted emergency rule making to classify the invasive freshwater mussel as a Prohibited Level 1 invasive species statewide. This designation makes it illegal to possess, introduce on or into a water body or property, or traffic (transported, bought, or sold) without authorization.
What are golden mussels?
Native to Southeast Asia, golden mussels have spread to other areas of Eastern Asia and parts of South America, likely attached to the hull (bottom or sides) of transoceanic ships or in the contaminated ballast water used to stabilize vessels when empty. Though a freshwater species, golden mussels can survive short periods in saltwater, or brackish water — a mixture of saltwater and freshwater — allowing them to survive in areas of estuaries that are regularly flushed with freshwater, or short distance transoceanic voyages.
Like their name suggests, golden mussels have a golden to yellowish-brown shells with a purple mother-of-pearl layer on the inside of the shell. Their larval stage is microscopic, and adults usually measure 3/4 to 1 1/4 inches long but can grow up to 2 inches — smaller than most native mussels found in Washington’s lakes and rivers.
The native Mytilus trossulus, known by many common names including foolish, blue, or bay mussel, a small species of native mussel common on marine docks and piers, could be mistaken for the invasive species. Typically black, foolish mussels can be golden or brown and are often found in areas with other marine species like common blue mussels, anemones, crabs, and barnacles.
Invasive golden mussels are typically found in areas with lower salinity, such as brackish waters, river mouths, and estuaries, and are not expected in the marine areas where foolish mussels are found along with our other native saltwater mussel species: blue mussels and California mussels.
Risk to Washington
Like invasive freshwater quagga and zebra mussels, another Prohibited Level 1 species, golden mussels have byssal threads — rope-like threads that allow them to attach to surfaces like rocks, water intake pipes, watercraft, and even native mussels. No freshwater mussels native to Washington have byssal threads.
Free from predators and conditions that limit their growth in their native range, they can quickly form dense carpets, taking over habitats critical for native species leading to irreversible habitat changes and loss. Habitat loss and impacts on native species have broader impacts statewide as declining populations can disrupt ecosystems and food webs for fisheries, wildlife, and people.
Due to their ability to attach to surfaces with their byssal threads, golden mussels can damage critical infrastructure by clogging water intakes and pipes used by utilities, navigational locks, irrigation systems, and hydropower dams putting billions of dollars in industry and trade at risk. Invasive golden mussels in Brazil were estimated to be responsible for more than $120 million in annual damages to the electricity sector in 2018.
Next steps
The emergency rule prohibiting golden mussels became effective immediately and will remain in effect for 120 days. During this time, WDFW will initiate permanent rulemaking, including a public comment period and opportunities for stakeholder engagement.
This process ensures that long-term protections reflect both the latest science and input from Washington communities, tribal nations, water users, and industry partners.
Washington’s readiness: monitoring and rapid response
Washington has spent more than a decade preparing for invasive mussels — and that preparation is now being put to the test.
WDFW maintains a statewide early detection and monitoring program designed to find invasive mussels before they can be widely established. This includes:
· Sampling for microscopic larvae in the water column
· Sampling for genetic materials using environmental DNA (eDNA) technology
· Deploying sediment samplers in risk-risk waterbodies
· Monitoring priority lakes, rivers, and reservoirs statewide
If golden mussels are detected, Washington is prepared to activate a rapid response framework to contain and, where possible, eradicate the infestation. These efforts are coordinated with co-managers, tribes, and partners both statewide, regionally, and nationally to ensure a unified and successful response.
Learn more about sampling methods on our YouTube channel.
Prevention is our best defense
Preventing introduction is far more effective — and far less costly — than managing an established population of golden mussels. Once invasive mussels take hold, eradication is often not possible.
This is why Washington state law requires all watercraft and aquatic conveyances like fish tankers or construction equipment to stop at mandatory watercraft inspection stations. These inspections are critical to protecting fisheries, infrastructure, and recreational opportunities across the state. Stopping at check stations is mandatory and key to protecting our waters (RCW 77.135.120).
WDFW provides free watercraft inspections and decontamination for motorized and non-motorized watercraft. Inspectors look for AIS hitching a ride on watercraft and gather important information to assess risk and determine if aquatic invasive species, such as golden mussels, are present. If needed, staff will provide a decontamination after the inspection free of charge.
You can help
While WDFW works to intercept invasive mussels at Washington’s borders, anyone who works or recreates on the water can help prevent the spread of invasive species like golden mussels.
Any time you go out on the water, remember to Clean, Drain, and Dry all your gear and watercraft — both motorized and non-motorized. Each time you leave a waterbody:
- Clean off plants, animals, and mud.
- Drain all water from your equipment.
- Dry everything thoroughly before entering a new waterbody.
If it’s been in the water, it could be contaminated with AIS. Practicing Clean, Drain, Dry every time helps stop the accidental spread of invasive species. It’s illegal to transport AIS from one waterbody to another in Washington, but remembering to Clean, Drain, Dry ensures you won’t be at risk of receiving fines up to $5,000 or a year in jail (RCW 77.135.220). With your help, Washington can keep invasive mussels out of our waters.
If you find something suspicious, report your potential AIS sighting to the Washington Invasive Species Council on their website or app. Reports are distributed to WDFW and other partners to respond. If you have questions, call the AIS hotline at 1–888-WDFW-AIS.
We still have time to prevent golden mussels from establishing in our waters, but time is running out. The recent Oregon interception shows how quickly this threat is moving but it also demonstrates that prevention works.
With your help, watercraft inspections, and coordinated actions, we can avoid the ecological and economic impacts threatened by invasive golden mussels. Protecting our waters depends on us.
