With summer in full swing, it’s time to hit the water for some fun in the sun. Whether you’re swimming, fishing, or boating, aquatic activities have the potential to spread aquatic invasive species (AIS). This summer’s newest AIS of concern? The invasive freshwater golden mussel (Limnoperna fortunei).

In April this year, Oregon Department of Fish and Wildlife (ODFW)  confirmed the interception of a golden mussel-fouled watercraft at the Ashland Boat Inspection Station. First detected in North America in San Joaquin County, California in 2024, golden mussels have since been found throughout Upper San Francisco Bay/Sacramento River Delta system and waters connected to the California Aqueduct.

The recent Oregon interception confirms an active pathway for invasive mussels to spread northward through movement of contaminated recreational boating and aquatic equipment – a common route for the spread of AIS.

Native to southeast Asia, golden mussels have spread to other parts of Asian and South America, most likely on the hulls of shipping vessels or in released contaminated ballast water.

While not known to be established in Washington, federal and state risk assessments identify golden mussels as a high-risk invasive species. WDFW’s risk assessment identified severe risks to native species, water-dependent industries, and cultural resources.

An imminent threat to Washington

Golden mussels pose a threat to Washington’s environment, economy, health, and way of life similar to invasive freshwater quagga and zebra mussels (QZM). These prolific filter feeders reproduce rapidly and can alter food webs and impact water quality irreversibly, changing habitats critical for native fish and wildlife species, including threatened and endangered species.

Like QZM, golden mussels can attach to surfaces via rope-like threads, called byssal threads, on the hinge side of their shell, quickly taking over habitats and clogging water intake pipes, damaging critical infrastructure.  

Golden mussels can tolerate a wider range of water temperatures and salinity than other species of invasive freshwater mussels, allowing them to establish in areas where QZM could not survive. Though a freshwater species, golden mussels can survive short periods in saltwater and brackish water – a mixture of saltwater and freshwater. This allows them to survive in areas of estuaries regularly flushed with freshwater or over short-distance transoceanic voyages.

What’s being done

WDFW has undertaken an emergency rule to classify golden mussels as a Prohibited Level 1 invasive species statewide in response to the imminent threat of introduction and spread to Washington’s waters. As a Prohibited Level 1 species, live golden mussels may not be possessed or retained, introduced on or into a water body or property, or trafficked (transported, bought, or sold), without Department authorization, a permit, or as otherwise provided by rule.

Along Washington’s roadways, watercraft inspectors are on high alert. As of April 2026, inspectors have examined more than 5,800 watercraft (2,000 more than this time last year), performing 451 decontaminations, and intercepting four quagga and/or zebra mussel-fouled watercraft. To date, there have been no interceptions of golden mussel-fouled watercraft in Washington.

WDFW AIS prevention staff sample water bodies year-round for the presence of invasive freshwater mussels. With the additional risk posed by golden mussels, prevention staff have increased and expanded sampling efforts into more brackish waters where the species could establish. Identifying potential infestations early is critical to preventing establishment. In 2025, monitoring staff used a variety of sampling methods at more than 300 waterbodies statewide and are prepared should invasive mussels be detected.

Prevention is our best defense

The most effective tool for AIS management is prevention, but successful prevention requires everyone’s help. Protect our waters by practicing clean, drain, and dry practices every time you leave the water, stop for mandatory watercraft inspections, and decontaminate watercraft and equipment that could be contaminated with AIS.  

If your gear or watercraft has been used in waters suspected or known to have AIS, contact WDFW's Aquatic Invasive Species hotline at 1-888-WDFW-AIS (1-888-933-9247) or send an email to ais@dfw.wa.gov. 

If you find something suspicious, report potential AIS to the Washington Invasive Species Council on their reporting website or app. Don’t forget to include the location where the AIS was spotted (GPS coordinates are ideal) and one or more photos.

In addition to implementing prevention practices, we encourage the public to report detections of potential invasive freshwater mussels. The most distinct identifying feature of golden, quagga, and zebra mussels are their byssal threads that allow them to attach to surfaces like rocks, plants, water intake pipes, watercraft, and even native freshwater mussels. No native freshwater mussels have byssal threads

While native marine mussels have byssal threads, invasive quagga and zebra mussels are only found in freshwater. Although golden mussels can survive for a time in brackish water, they cannot survive in marine habitats. If you spot a mussel in freshwater with byssal threads, report your potential AIS sighting to the Washington Invasive Species Council as above. Be sure to include the location where the sighting occurred (GPS coordinates are ideal) and, if possible, one or more photos of the potential AIS.

Visit  WDFW’s golden mussel webpage for more species information. The Department’s Clean, Drain, Dry webpage has resources for helping prevent the accidental transportation of AIS and our watercraft inspection station webpage can help you find a station along your route.