This invasive diatom, previously unknown in eastern North America, was discovered in Bloomfield, VT in June, 2007. The diatom, which may have come in on the soles of contaminated fishing waders, threatens the region's fine fisheries, especially the wild brook trout. Visit the states' new official web site to learn more.

Infestation Locations

Since its discovery in the designated "natural" segment of the Connecticut River in Bloomfield, Vt., and Maidstone, NH, didymo has since been found in the Connecticut River from Perry Stream in Pittsburg to the Old Wyoming Dam in Guildhall/Northumberland. It is also in the White River near Bethel, Vermont, the Batten Kill in southwestern Vermont, and at least two prime trout streams in the Adirondacks, including the East Branch of the Delaware River and the Batten Kill.


Anglers, kayakers, canoeists, boaters and jet skiers can all unknowingly spread didymo by transporting the cells on boats and other gear.

Eradication and Control

There are currently NO known methods for controlling or eradicating didymo once it infests a water body.


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.

How to clean non-absorbent items

o Detergent or salt: soak or spray all surfaces for at least one minute in a 5% solution (by volume) of dishwashing detergent or salt (7 ounces of detergent or salt added to water to make one gallon); or

o Bleach: soak or spray all surfaces for at least one minute in a 2% solution (by volume) of household bleach (3 ounces of bleach added to water to make one gallon); or

o Hot water: soak for at least one minute in very hot water kept above 140 °F (hotter than most tap water) or for at least 20 minutes or in hot water kept above 115 °F (uncomfortable to touch).

How to clean absorbent items

Absorbent items require longer soaking times. For example, felt-soled waders require:

o Hot water: soak for at least 40 minutes in hot water kept above 115 °F; or

o Hot water plus detergent: soak for 30 minutes in hot water kept above 115 °F containing 5% dishwashing detergent.

If cleaning is not practical

Dry - If cleaning is not practical, after the item is completely dry to the touch, wait an additional 48 hours before contact or use in any other waterway. Check thick absorbent items closely to assure that they are dry throughout.

Equipment and gear can also be placed in a freezer until all moisture is frozen solid.

NOTE: If cleaning, drying or freezing is not practical, restrict equipment to a single water body.