OLYMPIA – Washington Department of Fish and Wildlife (WDFW) has undertaken emergency rule making to classify golden mussels (Limnoperna fortunei) 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.
On April 9, 2026, Oregon Department of Fish and Wildlife (ODFW) confirmed the interception of a watercraft fouled with golden mussels at the Ashland Boat Inspection Station. First detected in North America in California's Sacramento-San Joaquin Delta in 2024, this interception confirms an active pathway for invasive mussels to spread northward through movement of contaminated recreational boating and aquatic equipment.
Risk to Washington
While not currently known to be established in Washington, federal and state risk assessments, including a 2025 ecological risk screening summary by the U.S. Fish and Wildlife Service and the United States Geological Survey Nonindigenous Aquatic Species resource system, identify golden mussels as a high-risk invasive species. WDFW's risk assessment similarly identified severe risks to native species, water-dependent industries, and cultural resources.
Golden mussels pose similar threats to the environment, economy, and health as invasive quagga and zebra mussels, which are also Prohibited Level 1 species in Washington. Golden mussels can tolerate a wider range of water temperatures and salinity, including brackish waters and estuaries. As prolific filter feeders, they alter food webs and impact water quality. Due to their ability to attach to surfaces via rope-like threads on the hinge side of their shell called byssal threads and rapidly reproduce, they can irreversibly change habitats critical for native fish and wildlife species, including threatened and endangered species.
The ability to attach to surfaces also enables these invasive mussels to cause significant biofouling to infrastructure by clogging intake pipes critical for hydropower systems, irrigated agriculture, drinking water, and sewage. In Brazil, invasive golden mussel establishment led to an estimated $120 million in impacts to the electricity sector. Like potential impacts from quagga and zebra mussels, hydropower and water infrastructure management and mitigation costs could exceed more than $100 million annually if they become established in Washington.
Prevention and protecting our waters
If a vessel has been in the water, it could be contaminated by aquatic invasive species (AIS) like golden mussels.
Though largely preventable, overland movement of recreational watercraft and aquatic equipment are major pathways of AIS introduction and spread. Practicing clean, drain, dry; stopping for mandatory watercraft inspection as required by state law; and performing decontamination, have proven successful at stopping the spread of AIS but require participation from everyone who works or recreates in the water.
In Oregon, stopping at ODFW's Ashland Boat Inspection Station allowed staff to decontaminate the golden mussel-fouled vessel and properly dispose of all attached invasive mussels preventing them from accidentally being introduced into Oregon.
In Washington, watercraft inspectors are off to a record start in 2026, inspecting 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.
In 2025, WDFW staff inspected more than 61,000 watercraft — a new record high number of inspections for the state, decontaminated 3,328 boats suspected of or at high-risk of carrying AIS, and intercepted 21 quagga and/or zebra mussel-fouled watercraft. To date, there have been no interceptions of golden mussel-fouled watercraft in Washington.
Invasive freshwater mussels are not known to be established in Washington so 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.
Reporting aquatic invasive species
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.
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.
WDFW's Aquatic Invasive Species (AIS) Division works to prevent the introduction of AIS and stop or slow their spread, protecting Washington's waters, fish, wildlife, and habitat.
The Washington Department of Fish and Wildlife works to preserve, protect, and perpetuate fish, wildlife and ecosystems while providing sustainable fish and wildlife recreational and commercial opportunities.
Request this information in an alternative format or language at wdfw.wa.gov/accessibility/requests-accommodation, 833-885-1012, TTY (711), or CivilRightsTeam@dfw.wa.gov.