(802) 763-7733 info@whiteriverpartnership.org 4266 VT Rte. 14, South Royalton, VT 05068

Didymo Information


Felt-soled wading boots prohibited in Vermont waters as of April 1, 2011.

In an effort to curb the spread of aquatic invasive species in Vermont rivers, the Vermont legislature has enacted, and the Governor signed into law, a ban on use of felt-soled waders in Vermont waters effective April 1, 2011. Felt-soled waders have been strongly implicated in the spread of several invasive species including didymo, as well as New Zealand mudsnail and Myxobolus cerebralis, the parasite that causes whirling disease in trout.

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 Vermont?

As of summer 2010, didymo has been confirmed in the following Vermont river systems: Battenkill River, Gihon River, Mad River, Passumpsic River, and White River. Didymo has been confirmed as far upstream as Rochester on the main stem of the White River; all sites downstream have the potential to develop nuisance blooms.

For the latest known distribution of didymo in Vermont and beyond, check out the Vermont Water Quality Division website.

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 detailed information about decontaminating specific types of gear, visit this link.

Where can I get more information?

Visit the Vermont Water Quality Division website or the Vermont Fish and Wildlife Department website to get more information about didymo.

The WRP is working to raise awareness about didymo in the White River watershed by distributing an informational brochure to fishing license agents and by posting informational signs at public access sites.