Quagga and zebra mussels

Download the quagga and zebra mussel rack card (PDF) for information offline. 

An imminent threat

Where introduced, freshwater quagga and zebra 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. Quagga and zebra mussels are not currently known to be established in Washington, but the risk that they will be introduced to our waters is significant.

Environmental risk

Invasive zebra mussels attached to a native mussel.
Photo by U.S. Fish and Wildlife Service
Invasive zebra mussels attached to a native species of mussel. 

If introduced and able to establish in Washington, quagga and zebra mussels are expected to take over habitats critical for native species like steelhead and salmon and threaten billions in investments in salmon recovery in the Columbia River Basin, freshwater ecosystems, and fish and wildlife resources. Habitat destruction and impacts to native species have broader impacts statewide with decreased salmon populations leading to less food for the endangered Southern Resident killer whale population, which relies on Chinook salmon. 

Economic risk

Zebra mussels clogging the inside of a pipe.
Photo by Craig Czarnecki, Michigan Sea Grant
Invasive zebra mussels clogging the inside of a pipe.

Establishment would also lead to major economic impacts and would likely harm human health. Management and mitigation costs will exceed $100 million each year to keep power and water infrastructure running, with similar impacts expected for other critical infrastructure systems like irrigated agriculture and wastewater systems.

Preventing quagga and zebra mussels from entering Washington’s waters is crucial. WDFW and partners are working to protect our waters, but prevention requires everyone’s help. If you recreate or work in Washington’s waters, you play a key role in preventing the spread of invasive mussels. 

Description and range

Description

Invasive mussel with clearly visible byssal threads in front of other invasive mussels.
Photo by WDFW
Invasive mussel with visible byssal threads. 

Quagga and zebra mussels are freshwater mussels usually measuring an inch or less, relatively small compared to native freshwater mussels which usually measure around 5 inches. Adult quagga mussels are slightly larger than zebra mussels. 

Unlike native freshwater mussels, quagga and zebra mussels have thread-like ropes called byssal threads on the hinge edge of their shell that allow them to attach to surfaces like rocks, plants, water intake pipes, watercraft, and even native freshwater mussels. These threads make it easy to accidently transport them from infested waterbodies to new ones and allows them to take over habitats effectively destroying them for native species, cover submerged surfaces, and clog pipes connected to critical infrastructure. 

While native marine mussels have byssal threads, invasive quagga and zebra mussels are only found in freshwater. If you spot a mussel in freshwater with byssal threads, report it as soon as possible. Don’t forget to take photos! 

Quagga mussels are light tan to almost white with narrow stripes across a fan-shaped, rounded shell. 

Zebra Mussels are mostly white to cream-colored with jagged brown or black stripes across the D-shaped shell.

Lifecycle

Quagga and zebra mussel larvae are microscopic and free-floating, using water currents to carry them to new areas to infest. As they age, the larvae gain the ability to swim and settle as juveniles wherever their byssal threads can attach. Both species mature in the first or second year and female mussels can produce millions of eggs per year. 

Free from natural predators in their native range, they can reproduce and take over habitats quickly once established. 

Invasive quagga and zebra mussel lifecycle with size comparison between native mussels and invasive mussels.
Lifecycle of invasive quagga and zebra mussels and a size comparison between native mussels and invasive mussels. 

Introduction to the U.S.

Freshwater quagga and zebra mussels, native to the Caspian Sea were first detected in the Great Lakes in the 1980s. Believed to have traveled to the U.S. in the ballast water of trans-oceanic ships, they have since spread to more than 30 states and parts of Canada. While not currently known to be established in Washington, they have been intercepted on watercraft at the state border, attached to imported aquarium moss balls, and in the Snake River in Idaho.

Prevention

Early detection monitoring

WDFW staff member benthic sampling with a ponar grab sampler.
Photo by WDFW
Benthic sampling with ponar grab sampler.

Identifying invasions early is critical to preventing quagga or zebra mussels from establishing populations. Each year, WDFW collects early detection monitoring samples at waterbodies across the state to monitor for invasive mussels.

Emergency planning

Should quagga or zebra mussels be detected in Washington, WDFW is prepared to respond rapidly to contain and limit the impacted area. 

In 2019, the state worked alongside state, federal, and tribal government partners on a first-of-its-kind invasive mussel rapid response mock exercise at Lake Roosevelt in Kettle Falls, WA. The exercise included deploying and testing a containment system, boat inspections, public notifications, a decontamination station, shoreline surveys by trained mussel-sniffing dogs, and in-water monitoring by skilled divers and scientists. 

Several people wearing white hazard suits on a dock.
Photo by Alan Hageman, National Park Service
Rapid response mock exercise at Lake Roosevelt. 

How to help

If you recreate or work on the water, you play a key role in preventing the spread of aquatic invasive species. Overland transport of invasive mussels on contaminated gear, watercraft, and aquatic equipment is preventable by practicing Clean, Drain, Dry and taking steps to decontaminate equipment used in infested waters. 

Clean, Drain, Dry

Man cleans visible plants from watercraft engine.
Photo by WDFW

The best way to prevent overland transportation of quagga and zebra mussels is to clean, drain, and dry your gear, watercraft, and equipment. 

If it’s been in the water, remember to Clean, Drain. Dry. 

Decontaminate

Invasive mussels are small, and larvae are microscopic meaning you’re not likely to see them hitching a ride on your gear, watercraft, or equipment. If you’ve been recreating or working in a waterbody known to be infested with quagga or zebra mussels, decontamination is necessary. You can check if a waterbody is known to be infested by visiting the U.S. Geological Survey map. 

If you suspect or know your gear or watercraft has been used in infested waters, contact WDFW's Aquatic Invasive Species hotline at 1-888-WDFW-AIS (1-888-933-9247). 

Watercraft inspections

Two people wearing yellow vests standing in front of a small building with a watercraft inspections sign.
Photo by WDFW

WDFW provides free watercraft inspections for motorized and non-motorized watercraft. Stopping is mandatory and important for preventing the introduction and spread of AIS (RCW 77.135.120). 

Inspectors look for AIS, including quagga and zebra mussels, hitching a ride on your watercraft and gather important information to protect Washington’s waters. If needed, staff will provide a free decontamination after the inspection.  

An invasive mussel detection dog may assist with the inspection of your watercraft. Mussel detection dogs are trained to identify only the presence of quagga and zebra mussels which can be difficult to locate visually. 

Speed up your inspection by remembering to Clean, Drain, and Dry your watercraft!

Proper disposal

Quagga and zebra mussels can contaminate aquarium plants, water, and decorations and due to their size and microscopic larvae may go undetected. Always dispose of domesticated plants, animals, and potentially contaminated items properly to avoid accidental introduction of AIS. 

Regulations

Quagga and zebra mussels are not known to be established in Washington and are a prohibited level 1 species that may not be possessed, imported, purchased, sold, propagated, transported, or released into state waters without department authorization, a permit, or as otherwise provided by rule (RCW 77.15.253).

Prevent transportation of AIS, including invasive mussels, by practicing Clean, Drain, Dry and stopping at all mandatory watercraft inspection stations. Transportation of AIS carries a fine of up to $5,000 and up to a year in jail (RCW 77.135.010). 

Out-of-state AIS prevention permit

Operators of watercraft not registered in Washington State, seaplanes, and commercial transporters of specified vessel types, must buy an Aquatic Invasive Species Prevention Permit. These permits are valid for one year and may be purchased for $24 online or from any of WDFW’s authorized license dealers.