Didymo Resources

What is Didymo?

Didymo is the common name for Didymosphenia geminata, an invasive freshwater diatom species (microscopic algae). 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. It is actually these stalks that are more problematic than the algae. The algae will eventually die off and decompose, while these stalks tend to persist for several months on the river bottom.

Where has Didymo been found in New England?

As of October 2007, Didymo has been confirmed in the Connecticut River near Bloomfield, VT; the White River downstream of the Stony Brook confluence in Stockbridge, VT; the Battenkill River in both Vermont and New York; and portions of the Delaware River in New York. Due to the nature of spread, biologists are concerned that any areas downstream of these four rivers could eventually show growing colonies of Didymo.

Don’t Spread Didymo

Although there is no known method of removing or killing the algae once it is in the river, WE CAN STOP IT FROM SPREADING! Simply CHECK, CLEAN, and DRY each time you use the White River.

CHECK: Before you leave the river, check gear for clumps of algae or sediment; leave it at the site.

CLEAN: Choose the treatment best suited to your gear and situation:

Non-absorbent items (such as boats): Scrub all surfaces for 2 minutes in a 2% bleach solution or a 5% solution of very hot water (120 degrees) and dishwashing detergent.

Absorbent items (such as felt-soled waders): Soak for at least 30 minutes in a 5% solution of very hot water (120 degrees) and dishwashing detergent. Alternately, freeze an item until solid to kill didymo.

DRY: Items must be completely dry to the touch, inside and out, then left to dry for another 48 hours. Slightly moist didymo can survive for months.

For more information about decontaminating different types of gear, visit this link.

Where can I get more information?

Visit the New Hampshire Exotic Species website to get more information about Didymo. This site includes a list of frequently asked questions, a Didymo identification table, a PDF file of the Didymo sign posted around the Connecticut and White River watersheds, a map of confirmed Didymo blooms, and a link to the EPA Didymo website.