Didymo Resources

Didymosphenia geminata, commonly known as Didymo, is an invasive freshwater algae recently found in the Mad River.  In the Northeast, it is known to be present in the Battenkill, White and Connecticut Rivers, and it has also been identified within the past several years in the Western US and in New Zealand. 

Didymo, a.k.a. Rock Snot, can cause nuisance "blooms", covering rocky stream bottoms with dense mates of algae and potentially affecting trout habitat and food sources.  Didymo can also impact recreation as it can be very unappealing.


Can Didymo Affect My Health?

No.  Didymo has not been shown to impact the health of humans or pets.  We encourage you to enjoy the Mad River as you have in the past, and please also follow the steps below in order to prevent the spread of Didymo.

Where has Didymo been found in the Mad River?

The presence of Didymo has been confirmed by an Agency of Natural Resources expert near Riverwatch Lane and at Riverside Park in Warren.

Friends of the Mad River staff and volunteers have also spotted the algae at the following locations:

Once Didymo is present in a river, it can easily spread downstream, and it is likely to be found in any location downstream where there is suitable habitat.  Didymo grows in fast moving, shallow water where there is a rocky bottom and sufficient sunlight.

What Can I Do?

Didymo cannot be removed from a river once it is present.  You can work to prevent the spread of Didymo upstream, to tributaries, or other waterbodies.  Didymo can only spread upstream in a waterbody or to another waterbody if it is carried by humans or animals.  Didymo can "hitchhike" on you or your gear, so it is important to follow these steps when using the river.

Donít Spread Didymo!

CHECK, CLEAN, and DRY each time you use the Mad 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.

Where Can I Learn More?

The Vermont Department of Environmental Conservation Didymo Website

New, updated website about Didymo in VT 

Times Argus Article about the discovery of Didymo in the Mad River 

The Aquatics Nuisance Species Task Force

A national organization dedicated to the prevention and control of invasive nuisance aquatic species.

Protect Your Waters--Stop Aquatic Hitchhikers Campaign

The "Stop Aquatic Hitchhikers" Program is dedicated to the broad scope of aquatic invasive species.