What is Didymo?
Originally found in Scotland, northern Europe and Asia, Didymo is an invasive freshwater alga that can form massive blooms in rivers and streams and potentially disrupt an ecosystem. This species historically was found in fast-flowing, cold, clean waters but its ecological range has been increasing. It was first found in Maryland this spring in the Gunpowder Falls in Baltimore County.
Didymo form long stalks which combine into heavy, thick mats that can smother a stream bottom. Didymo mats, also called “rock snot,” look slimy, but feel like wet cotton or wool. They can be white, yellow or brown. The mats occur in late winter and early spring and can damage the habitat for an extended period of time by choking out bottom-dwellers and removing food organisms for game fish and other aquatic species.
There is no human health risk associated with Didymo, but anglers and outdoor enthusiasts can unwittingly spread it from one waterway to another through contaminated fishing gear and boats. A single cell can contaminate a new waterway.
The Department of Nature Resources (DNR) advises anglers and boaters to help prevent spread of the invasive species by scrubbing dirt and debris from anything that comes into contact with a waterway. Equipment can be easily disinfected with a five percent salt solution or by scrubbing well with dish detergent. If disinfection is not possible, let equipment dry completely for at least 48 hours. Anglers may want to consider having two sets of equipment in order to move safely from one spot to another.