DEEP: DEP Reports Didymo Discovered in the West Branch Farmington River

March 29, 2011
DEP Reports Didymo Discovered in the West Branch Farmington River
First Confirmation of this Invasive Species in Connecticut

The Connecticut Department of Environmental Protection (DEP) today announced that the highly invasive freshwater alga, Didymosphenia geminata, known as "didymo", has been discovered in the West Branch Farmington River, a very popular trout stream in northwestern Connecticut.

 One of the numerous clumps of didymo
 found in the West Branch Farmington River.

The presence of didymo was first confirmed in the northeastern United States in 2007, and has since spread to other popular trout streams in a number of northeastern states (New Hampshire, Vermont, New York, Pennsylvania, Maryland, West Virginia and Virginia). This is the first report of didymo in Connecticut.

DEP first learned of the possible presence of didymo in the West Branch Farmington River from several anglers on March 18th. One of these anglers also provided an initial sample to DEP. Following initial review by DEP staff, samples were sent to the Vermont Department of Environmental Conservation where biologists have direct experience identifying didymo. Late last Friday, Vermont officials confirmed that the sample was indeed didymo.

"This find is very troubling," said DEP Deputy Commissioner Susan Frechette. "Extensive blooms of this organism can harm the river ecosystem and decrease its recreational and economic value. In an effort to confirm identification, staff from DEP’s Bureau of Water Protection and Land Reuse surveyed a number of sites in the river and a major tributary along a seven mile stretch of the West Branch Farmington River in Hartland and Barkhamsted. Unfortunately numerous clumps of didymo were found at all the surveyed sites in the river downstream of the Riverton Bridge. Once didymo has spread, there’s no practical way to remove it from a river."

Didymo is most frequently found in cold, relatively shallow streams and rivers having a rocky bottom, characteristics that are also typical of good trout habitat. During blooms, didymo can form thick mats of material that feel like wet wool and are typically gray, white and/or brown, but never green in color. These mats form on the bottoms of rivers and streams and can potentially smother aquatic plants, aquatic insects and mollusks, impact fish habitat, and alter aquatic food chains. Dense mats of didymo can also reduce the recreational and aesthetic value of the affected river. Since didymo also prefers areas open to sunlight, it is not anticipated that this species will become problematic in smaller headwater streams as long as they have well shaded riparian and naturally forested riparian areas.

Humans are the primary vector responsible for the recent spread of didymo. Anglers, kayakers and canoeists, boaters and jet skiers can all unknowingly spread didymo. The microscopic cells can cling to fishing gear, waders (felt soles can be especially problematic), boots and boats, and remain viable for months under even slightly moist conditions. To prevent the spread of didymo to additional waters, DEP asks that anglers, especially those who also fish the Farmington River or streams outside Connecticut, and other users practice CHECK, CLEAN, DRY procedures.

  • CHECK: Before leaving a river, stream or lake, remove all obvious clumps of algae and plant material from fishing gear, waders, clothing & footwear, canoes & kayaks, and anything else that has been in the water and look for hidden clumps. Leave them at the site. If you find any later, clean your gear and dispose of all material in the trash.
  • CLEAN: Soak/spray & scrub boats and all other "hard" items for at least one minute in either very hot (140°F) water, a 2% bleach solution, or a 5% dishwashing detergent solution. Absorbent materials such as clothes and felt soles on waders should be soaked for at least 40 minutes in very hot water (140°F), or 30 minutes in hot water (115°F) with 5% dishwashing detergent. Freezing thoroughly will also kill didymo.
  • 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.

The above procedures will also be effective against other unwanted organisms.

Didymo is just one of a number of aquatic invasive species that have either invaded the state or are threatening to do so. DEP will continue its work to combat the spread of invasive species, focusing on prevention, education and early detection. DEP is an active member of the Invasive Plants Council and supports both an Invasive Plant Program and an Aquatic Nuisance Species Program in collaboration with the University of Connecticut. When available, DEP has provided funding from a variety of sources to educate the public on the threats posed by invasive species and to combat specific invasive species including fanwort, water chestnut and hydrilla. In addition, the DEP has recently proposed new regulations to prohibit the possession or importation into the state of a number of invasive invertebrates.

Since its discovery in the northeast in 2007, DEP has taken additional precautions to prevent the introduction and/or spread of didymo (and other invasive species). DEP’s Inland Fisheries Division instituted an operational "Biosecurity" policy for its own field operations, including elimination of the use of felt-soled waders. Also, as part of its invasive species outreach efforts, informational fliers on didymo were distributed to many of the state’s bait & tackle shops and information about didymo has been prominently displayed in the CT Anglers Guide and on its website.

Individuals wishing to report possible sightings of didymo and other aquatic nuisance species can contact DEP’s Inland Fisheries Division at 860-424-3474. More information on didymo and other aquatic nuisance species can be found on the DEP website ( or in the CT Angler’s Guide ( An excellent source for detailed information on didymo is the Biosecurity New Zealand web site (