Emerging Pest Alert

First northeastern infestation of "didymo" in the United States

Scientific Name: Didymosphenia geminata

Describer: (Lyngb.) M. Schmidt

Common Name: didymo or rock snot

Title: First northeastern infestation of "didymo" in the United States


Significance: The Vermont Agency of Natural Resources confirmed that the aquatic nuisance algae known commonly as "didymo" or "rock snot" has invaded the northern areas of the Connecticut River, marking the first official report of Didymosphenia geminata in the northeastern United States. There have been increasing reports of the algae forming thick mats of cottony material on the bottoms of rivers and streams that can potentially smother aquatic plants and destroy fish habitat. 

Believed to be native to the far northern regions of Europe and Asia, didymo has been expanding its range and tolerance for warmer, more nutrient-rich water conditions during recent years in Europe and North America. In the past several years, didymo has expanded its range in the western United States and has infested rivers and streams in several southeastern states.

Issues of Concern: In 2004, didymo was discovered in New Zealand. Within 18 months it spread to 12 rivers on the South Island. New Zealand Biosecurity has instituted severe penalties for intentional spread of the algae, and is researching control and prevention methods. 

There are currently no known methods for controlling or eradicating didymo once it infests a water body. Preventing the spread of didymo is also difficult. Anglers, kayakers and canoeists, boaters and jet skiers can all unknowingly spread didymo as the algae easily clings to fishing gear, waders, boots, and boats. Didymo can remain viable for several weeks under even slightly moist conditions. Decontamination requires soaking clothing and equipment in hot water containing detergent, or a 2% bleach solution. Thoroughly drying clothing and equipment for a minimum of 48 hours can also be effective, but only if complete dryness is maintained.


Vermont Agency of Natural Resources - Press Release. July 06, 2007. Available online: http://www.anr.state.vt.us/site/cfm/PressRel/Detail.CFM?ID=1189  

Biosecurity New Zealand. Didymosphenia geminata. http://www.biosecurity.govt.nz/didymo