DEEP: CT DEP Advises Anglers And Boaters To Take Precautions To Prevent Spread Of "Didymo" Into Connecticut Waters

July 13, 2007

CT DEP Advises Anglers And Boaters
To Take Precautions To Prevent Spread
Of "Didymo" Into Connecticut Waters

Highly invasive alga found in Vermont in the Connecticut and White Rivers

The Connecticut Department of Environmental Protection today is advising anglers and boaters to be on the lookout for the highly invasive freshwater alga Didymosphenia geminata, known as "Didymo" and to take precautions to prevents its spread into Connecticut waters. The call was prompted when the Vermont Agency of Natural Resources recently confirmed that the alga has been found in the northern reaches of the Connecticut River near Bloomfield, VT, and at several sites along the White River, a tributary of the Connecticut River in central Vermont. This is the first official report of Didymo in the northeastern United States.

During blooms, didymo can form thick mats of cottony material (typically gray, white and/or brown, but never green in color) on the bottoms of rivers and streams that can potentially smother aquatic plants, aquatic insects and mollusks, destroy fish habitat, and negatively affect existing food webs. Didymo is most frequently found in relatively shallow streams and rivers having a rocky substrate. Didymo is not expected to be problem in the lower Connecticut River or in lakes; however, it could have a large impact on fish and other aquatic organisms if introduced to the state’s smaller rivers.

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. This microscopic alga can cling to fishing gear, waders (felt soles can be especially problematic), boots and boats, and remain viable for several weeks under even slightly moist conditions. It is recommended that water recreationalists practice CHECK, CLEAN, DRY procedures.

  • 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 either 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.

Thought to be native to far northern regions of Europe, Asia and probably North America, the geographical and ecological range of this freshwater alga has been expanding in recent years. Didymo has been spreading to diverse areas including British Columbia in Canada, the western US (especially Montana, South Dakota, Idaho and Colorado), New Zealand, and then into the southeast US (Arkansas, Tennessee, North Carolina, Virginia and West Virginia). Didymo, a microscopic alga, has also begun developing massive blooms that can sometimes extend for several kilometers of river.

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

For more information on Didymo, visit the US EPA Region 8 website:

or the Biosecurity New Zealand website: