AUGUSTA, Maine (IFW News)– With the discovery of the aquatic nuisance algae known commonly as “didymo” or “rock snot” on the Vermont/New Hampshire Border in the Connecticut River, the Maine Department of Inland Fisheries and Wildlife and the Maine Department of Environmental Protection are alerting boaters, anglers, kayakers, canoeists and others to take action to prevent this new invasive threat to Maine’s waters.

The confirmed discovery in Bloomfield, Vermont is the first official report of Didymosphenia geminata in the Northeastern United States.

Didymo can form extensive ‘blooms’ on the bottoms of rocky river beds, essentially smothering aquatic life forms such as macroinvertebrates (aquatic insects), native algae, and other organisms. Additionally, the physical appearance of the bloom is aesthetically unpleasing, and can reduce the recreational values of a waterbody. Didymo uses stalks to attach to rocks and plants in a river system. The diatom creates these stalks, which can form masses 10-12 inches thick on the river bottom, and trail for lengths of 2-3 feet in the current.

“Didymo can be spread by transporting a single cell, it forms dense mats, which can kill aquatic insect life, essentially starving out fish populations in the area,” said John Boland, Director of Fisheries for IFW. “The ease with which it can be spread is a real concern for anyone who enjoys Maine’s waters. All of Maine’s rivers and streams are at risk.”

Both IFW and DEP are urging anglers and other water recreationists to use these   procedures for preventing the introduction and spread of didymo:  Check, Clean and Dry.

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  • Check: Before leaving a river or stream, remove all obvious clumps of algae and look for hidden clumps. Leave them at the affected site. If you find any later, do not wash them down drains; dispose all material in the trash.
  • Clean: Soak and scrub all items for at least one minute in hot (140 degrees F) water, a two percent solution of household bleach or a five percent solution of salt, antiseptic hand cleaner or dishwashing detergent.
  • Dry: If cleaning is not practical, after the item is completely dry to touch, wait an additional 48 hours before contact or use in any other waterway.

“These steps are more than suggestions,” said IFW’s John Boland. “They’re absolutely essential for preserving the quality of Maine rivers and streams.”

There are currently no known methods for controlling or eradicating didymo once it infests a water body.  “Preventing the spread of Didymo is our best defense,” said Tom Danielson, a biologist with the Maine Department of Environmental Protection. “We have tested algae at over two hundred locations on Maine rivers and streams, and it has not yet been detected in Maine’s waters.”

Didymo is generally found in colder, low nutrient, high clarity streams. However, recently there have been discoveries of Didymo in rivers and streams in warmer climates, as well as streams with more nutrients, streams with moderate clarities and even some tannic (tea colored) waters. Didymo is currently found in Europe (Scotland, Poland) and it is spreading throughout the northwestern region of the US. It is also in Quebec, British Columbia and New Zealand.

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, including Virginia, West Virginia, Tennessee and North Carolina. 

In 2004, didymo was discovered in New Zealand.  Within 18 months it had spread to 12 rivers on the South Island, forming nuisance blooms at several locations.  New Zealand officials have instituted severe penalties for intentional spread of the algae, and are intensively researching control and prevention methods. 

If you feel that you have discovered didymo, please contact the Maine Department of Environmental Protection at 1-800-452-1942 or email This e-mail address is being protected from spam bots, you need JavaScript enabled to view it .