Didymo is also known as rock snot. (Maryland Department of Natural Resources)
Didymo attaches to rocks, plants and other submerged surfaces. (Maryland Department of Natural Resources)
Didymo prefers clear, cold 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
Didymo can be white, yellow or light brown and looks slimy, but actually has a rough texture similar to wet wool. It forms thick, heavy mats and can be tough to pull apart or remove from rocks.
Reproduction and Life Cycle
Didymo 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.
Did You Know?
- Didymo is also known as rock snot. It is a type of single-celled algae called a diatom.
- It is 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 Species of Concern in Maryland: Didymo – Maryland Invasive Species Council
- Do you know about Didymo? – Pennsylvania Fish & Boat Commission
- Didymo Fact Sheet – West Virginia Department of Natural Resources
- Didymo – USDA National Invasive Species Information Center
Quick Facts
Species
Invasive
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Habitat
Prefers clear, cold freshwater streams. Attaches to rocks, plants and other submerged surfaces by stalks that the algae cells secrete. Stalks weave together to form dense mats. Populations appear to peak in winter.
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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.
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Status
Stable
