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Didymo

Didymosphenia geminata

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:

• Found in Maryland’s Gunpowder Falls between Prettyboy and Loch Raven reservoirs in Baltimore County in 2008
• Discovered in the Savage River below Savage River Reservoir in 2009
• Native to Scotland and extreme northern Europe and Asia

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:

• Invasive Algae Found In Maryland – Maryland Department of Natural Resources
• Ask an Expert: What is Didymo? – Maryland Department of Natural Resources
• Invasive Species of Concern in Maryland: Didymo – Maryland Invasive Species Council