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Invasive Freshwater Plants and Algae

Rock Snot

  • Scientific Name

    Didymosphenia geminata - Visit ITIS for full scientific classification. 

  • Description


    • "Rock Snot" is a diatom (a type of single-celled algae).
    • This microscopic algae attaches to surfaces and grows in small clumps that become thick brown, tan, or whitish mats.
    • They create massive clumpy, or ropy fibrous strands.
    • Looks slimy, but feels like wet cotton or wool. 
  • Habitat
    • Attaches to plants, rocks and other surfaces in cool rivers and streams.
    • Prefers cold, clear waters with high flow, but there is concern that it's moving into warmer waters. 
  • Invasion Pathways and Distribution
    • This microscopic algae can be transported unknowingly on fishing gear, waders, wetsuits, clothing, truck tires, and even pet dogs. 
    • Has been reported to survive on objects out of the water in cool, dark, damp places for up to 40 days!
    • Recreational equipment is the most likely cause for spread.
    • See our Stop the Spread! page for instructional videos on how to decontaminate your field gear and the family dog!  
    • Native to northern Europe, and northern America.
    • Considered an "invasive native" due to it's expanding habitat range, and because of it's pesky impacts during high density nuisance blooms. 
  • Life History
    • Populations grow by vegetative cell division.
    • Uncertain for this species, but most diatoms also reproduce sexually.
    • During asexual cell division branching stalks are produced.
    • During a bloom (rapid growth) stalks form dense fibrous mats. 
  • Impacts
    • During a bloom, dense mats that cover stream beds are resistant to removal.
    • These dense mats may deplete the amount of dissolved oxygen and suitable habitats for certain invertebrate animals. 
    • May alter invertebrate species composition, favoring species that can feed on Rock Snot, while negatively impacting others. 
    • Can affect ecosystem function of the freshwater environments where the nuisance blooms occur.
    • The dense mats can foul infrastructure interfering with water flow. 
  • References and Useful Links

    For references by category and links to other useful AIS sites see our Learn More page.