Didymo (Didymosphenia geminata) aka 'Rock Snot' is spreading

It’s "snot funny" as rock snot is real and could be a potential aquatic invader in Michigan’s streams and lakes. Avoid spreading this aquatic hitchhiker by cleaning, draining and drying your watercraft and gear.

Photo courtesy of New Hampshire Department of Environmental Services
Photo courtesy of New Hampshire Department of Environmental Services

Characterized by the development of thick mat-like growths at the bottom of streams, Didymo (Didymosphenia geminata), or rock snot, can last for months. Didymo is an algae, declared as non-native invasive in New York and Pennsylvania, that sends tendrils into the water column in search of nutrients. Scientists at Dartmouth College in New Hampshire say it is native and occurs globally. Conditions for its growth are rare but increasing in the United States. Didymo is currently being monitored in Lake Superior.

Didymo threatens aquatic habitat by affecting the insect populations in trout and salmon streams and oligotrophic lakes. It is tan, brown or white, (not green); it does not feel slimy but has a texture somewhat like wet wool and is typically firmly attached and does not fall apart when rubbed with your fingers. The nickname “rock snot” is based purely on how it looks. Didymo, unlike other algae, prefers waters where phosphorous is low. Other “green” algae species thrive in phosphorous nutrient loaded waters.

It should be noted that the Didymo diatom or single-cell microscopic algae is not new. What is new is where the organism colonies are appearing. The New York Department of Environmental Conservation suggests that Didymo is spread by anglers, kayakers, canoers, tubers, boaters and other people engaging in water-based recreation who do not thoroughly clean their boats and gear. The microscopic parts of this species of algae and other water organisms can cling to boat parts, boots, waders, lures, hooks and line. Water recreationists are encouraged to clean, drain and dry their watercraft and gear between uses to help reduce the spread of invasive species in Michigan’s inland lakes and streams.

If you or your lake association is interested in watercraft checkpoints education or in a volunteer training to educate boaters at local public launches contact Michigan State University Extension educator Beth Clawson at clawsonb@anr.msu.edu. For more information about Clean Boats Clean Waters aquatic invasive species program or other water quality concerns contact MSU Extension. Water quality educators are working across Michigan to provide natural resources water quality educational programming and assistance. You can contact an educator through MSU Extension’s “Find an Expert” search tool using the topic “water quality.”

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