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Didymo

Didymosphenia geminata

Didymo forms thick, dense mats at the bottom of freshwater streams. (Tim Daley/Pennsylvania Department of Environmental Protection)
Didymo forms thick, dense mats at the bottom of freshwater streams. (Tim Daley/Pennsylvania Department of Environmental Protection)

Didymo is a type of algae that forms dense mats at the bottom of freshwater streams. It is an invasive species.

Appearance:

  • White, yellow or light brown
  • Forms thick, heavy mats
  • Looks slimy, but actually has a rough texture similar to wet wool
  • Tough to pull apart or remove from rocks

Habitat:

  • Prefers clear, cold freshwater streams
  • Attaches to rocks, plants and other submerged surfaces by stalks that the algae cells secrete. The stalks weave together to form dense mats.
  • Populations appear to peak in winter

Range:

Reproduction and Life Cycle:

  • Reproduces asexually when cells divide
  • As the algae cells divide, the stalks divide as well, forming a mass of stalks
  • Thick mats of didymo can remain for up to two months after the cells die

Other Facts:

  • Also known as rock snot
  • Didymo is a type of single-celled algae called a diatom
  • Not known to pose a health risk to humans
  • Anglers can help prevent didymo from spreading by replacing felt-soled waders with rubber-soled ones. Also, always thoroughly scrub, wash and dry waders and other fishing equipment after use.
  • You can report didymo sightings by calling the Maryland Department of Natural Resources at (410) 260-8287.

Sources and Additional Information:


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