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U.S. Fish & Wildlife Service
A pile of recently dead freshwater mussels collected by biologists from the Clinch River at Sycamore Island, Virginia.

Searching for Novel Pathogens in Freshwater Mussels

Updated September 1, 2026
A variety of recently dead freshwater mussels are easily seen from the shores of Wallen Bend on the Clinch River.

Unknown Cause of Mass Mortality Events in Mussels

Across the country, scenes of thousands of freshwater mussel shells scattered on the banks and bottoms of lakes and rivers haunts scientists. For the most part these mussel die-offs are unexplained and mysterious. Pollution and contaminants are a well known cause of mortalities but in the case of these die-offs there were no contaminants found. Unlike fish die-offs, mussel mass mortality events can be harder to find because the shells are often found under the surface of the water. Scientists are trying to better understand the scope of these events.

Two tanks side by side, one tank is filled with murky water and the other is clear with freshwater mussel resting on the bottom of the tank.

Why Does it matter?

Freshwater mussels are one of the most endangered species in the world. An estimated 70% of them are classified as being threatened or endangered. Mussels are incredible filterers of water and help keep water clean for humans, wildlife, fish, and anything else that needs clean water. They are known to filter out pharmaceuticals, personal care products, herbicides, flame retardants, E. coli, avian influenza, and reduce bacterial and nutrient loads. The ecosystems they are found in cannot afford to lose such an important organism. Identifying what is the cause of these mass mortalities is critical to the conservation of these species.

The Mussel Mortality Response Team

In partnership with other organizations, the Mussel Mortality Response Team is investigating pathogenic causes of these mortalities. The team is made up of the La Crosse Fish Health Center,Southwestern Virginia Ecological Services Field Office, UW–Madison, the U.S. Geological Survey Upper Midwest Environmental Sciences Center in La Crosse, and the U.S. Geological Survey National Wildlife Health Center in Madison. The team has been establishing a framework to study pathogens in mussels because, so little is known about it. So far, the team has identified over 600 novel viruses! We have studied mussel mortality events in Virginia, North Carolina, Wisconsin, Michigan, Ohio, Minnesota, Washington, and Oregon.

The team works on:

Publications

Explore more:
Hands hold up a small yellow mussel shell. The flesh of the recently deceased mussel sticks out from the shell. The person holding the mussel wears a striped blue shirt and overalls.

How can you help?

Please contact us with information on any historical or current freshwater mussel die-offs you’re aware. Feel free to reach out if you are conducting similar research and would like to collaborate.

Mussel Mortality Response Team Roles

Virology: Jordan Richard (USFWS) and Tony Goldberg (UW-Madison)

Bacteriology: Eric Leis (USFWS) and Sara Dziki (USFWS)

Assay Development: Isaac Standish (USFWS) 

Histology: Susan Knowles (USGS)

Malacologist: Diane Waller (USGS)