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News Species Spotlight: Brook floater

MassWildlife's Species Spotlight for March is the brook floater! Learn about brook floaters in Massachusetts, how MassWildlife biologists are working to protect this endangered species, and what you can do to help.
  • Division of Fisheries and Wildlife
  • MassWildlife's Natural Heritage & Endangered Species Program

Media Contact for Species Spotlight: Brook floater

Marion Larson, MassWildlife

Brook floater

The year 2020 marks the 30th anniversary of the Massachusetts Endangered Species Act (MESA)! To celebrate, MassWildlife will be highlighting one rare species each month as a Species Spotlight. Through the implementation of MESA, MassWildlife’s Natural Heritage and Endangered Species Program conserves and protects the most vulnerable animals and plants of Massachusetts and the habitats upon which they depend. Stay up to date on how MassWildlife is celebrating this important milestone by visiting


Common name: Brook floater
Scientific name: Alasmidonta varicosa
Size: Three inches in length
Range: Atlantic States and Provinces from New Brunswick, Canada south to Georgia
MA conservation status: Endangered
Federal conservation status: Not listed (listing not warranted in 2019)

Fun facts

  • Brook floater may live 15 or more years, which is pretty old for an invertebrate. Some of our other freshwater mussels in Massachusetts can live over 70 years!
  • Freshwater mussels can have very interesting names. Brook floater are sometimes called “swollen wedgemussel”.  Funny names of other freshwater mussels from other parts of the country include: “pocketbook”, “spectacle case”, “monkey face”, “sheepsnose”, “wartyback” and “orangefoot pimpleback”. 
  • Freshwater mussels are important to clean water and fish habitat. As filter feeders, they eat algae and bacteria in the water and clean our streams and ponds. They also provide structure the stream bottom or lakebed, improving habitat for other invertebrates and fish.
  • Freshwater mussels have a unique life cycle. Mussel larvae (babies) undergo a metamorphosis as parasites on fish hosts. The fish are not hurt during the metamorphosis. 
  • Some mussel species are “host specialists” and only use one to a few types of fish host, others are “generalists” and use many different fish species as hosts. Brook floater use a handful of fishes as hosts, including brook trout, minnows, and some sunfish.
  • Brook floater prefer medium sized streams with clear, cool, flowing water, and a streambed mixture of sand, cobble and boulders.

Threats and conservation

  • More than 70% of freshwater mussels in North America are considered needing conservation efforts.
  • Brook floaters are sensitive to stream fragmentation caused by dams as well as habitat degradation from pollution and development.
  • Only four populations of brook floater remain in the Commonwealth.
  • Brook floaters are listed as threatened or endangered by every state in which they occur. They are listed as endangered in Massachusetts. 
  • Since 2016, MassWildlife has been partnering with the US Fish & Wildlife Service and the University of Massachusetts, Amherst to research conservation needs of brook floater in Massachusetts. This research has resulted in a better understanding of host fishes and habitat used and identification of culture techniques for potential future reintroductions. Click here for more information on the Brook Floater Working Group. 

How you can help

  • MassWildlife's Natural Heritage and Endangered Species Program (NHESP) is responsible for the conservation and protection of over 400 rare animals and plants, including the bald eagle. NHESP's work is primarily funded through grants and donations from supportive citizens. Donate to NHESP today at 
  • Report sightings of rare species. If you have information on the location of a rare species or vernal pool and would like to help NHESP keep its database current, submit your observations through the Vernal Pool and Rare Species (VPRS) Information System. 

Media Contact for Species Spotlight: Brook floater

Division of Fisheries and Wildlife 

MassWildlife is responsible for the conservation of freshwater fish and wildlife in the Commonwealth, including endangered plants and animals. MassWildlife restores, protects, and manages land for wildlife to thrive and for people to enjoy.

MassWildlife's Natural Heritage & Endangered Species Program 

The Natural Heritage & Endangered Species Program is responsible for the conservation and protection of hundreds of species that are not hunted, fished, trapped, or commercially harvested in the state, as well as the protection of the natural communities that make up their habitats.