Didymo growth in the Batten Kill (NY section)		Didymo cell (400X magnification)

Background

Didymosphenia geminata, also known as ‘Didymo’ and ‘Rock Snot’ is a type of freshwater diatom or algae.  Individual cells can’t be seen without a microscope but they can produce a fibrous stalk that can develop into visible mats.  Though originally native to northern latitudes of Europe, Asia, and North America, it has undergone a recent large expansion in range and is now found in many western U.S. and Canadian rivers, some tailwater rivers in the south and, more recently, in Quebec and New Brunswick, as well as other locations around the world.  In addition to expanding its range, it’s also showing, in some locations, the potential to form nuisance blooms, during which it can form mats several inches thick that carpet a stream bottom.  Until 2006 it was unheard of in the northeastern U.S.  It was discovered during the summers of 2006 and 2007 in the Batten Kill (NY/VT), in 2007 in the Connecticut River (NH/VT), the White River (VT), and the Delaware River system (NY/PA), and in 2008 in the Gunpowder River (MD) and the Mad River (VT).

Click here to see the distribution of Didymosphenia geminata in Vermont (pdf, 212 KB)

Click here to see the North American distribution of Didymosphenia geminata (pdf, 115 KB)

Click on the following shortcuts or scroll down for more information about Didymo:

Things you should know about Didymo in Vermont

What does Didymo look and feel like?

How is Didymo a threat?

What impacts will Didymo have on our natural resources?

What is the Vermont Agency of Natural Resources doing about Didymo?

What precautions should river users take to avoid spreading Didymo?

How can I properly disinfect my recreational equipment?

What should I do if I think I’ve found Didymo?

Where can I find more information?

Things you should know about Didymo in Vermont:

• Didymo can have negative ecological, economic and aesthetic impacts in infested areas, but how it will affect Vermont waters is unknown.
• There are many examples of rivers where Didymo does do not form nuisance blooms or mats.  Surveys can locate viable cells but, for some reason, they do not undergo rapid growth and excess production of stalk material.  Scientists around the world are still attempting to determine what factors limit or support this bloom activity.
• Scientific studies conducted around the globe have yet to show conclusively that Didymo has significant impacts to trout fisheries.  However, it remains a priority of the Agency of Natural Resources to limit the alga’s spread throughout the region, as a precaution.
• Spread prevention is the only effective management tool.  There are no known methods of eradicating Didymo once established.
• Vermont ANR is cooperating with a number of federal, state and other entities to monitor and reduce the spread of Didymo in the Northeast.
• You can do your part to minimize the spread of Didymo by following best practices and disinfecting your gear when using Vermont waters (for specific suggestions see below).
• Disinfection and best practices not only help to reduce the spread of Didymo, but other invasive species and pathogens such as VHS (viral hemorrhagic septicemia) or whirling disease as well.  It’s simply good stewardship.
• Didymo can be present in a stream yet be invisible to the naked eye, particularly during the early stages of an infestation or following heavy flows.  This holds true for many other aquatic nuisance species as well as fish diseases.  River users should incorporate the suggested best practices (listed below), including proper gear disinfection before moving between ANY waterbodies, whether they are declared positive or not.

What does Didymo look and feel like?

• Light tan to brown in color
• Clumps feel like wet wool; never slimy or slippery
• Clumps resist being pulled apart, quite cohesive
• Expanding colonies may attach to plant stems, forming rope-like strands
• As stalks lengthen, they form ropy strands and may become white in color
• Dead strands may dry on rocks and look like tissue, fiberglass, or toilet paper

Click here for a guide to identifying Didymosphenia geminata. (pdf, 51 KB)

Click here for procedures to follow if you think you have found Didymo

Click here to download a Didymo sample submission form. (pdf, 23 KB)

Didymo clump on rock from the White River, Vermont (click on photo to enlarge, pdf, 143 KB)		Didymo on rock from Batten Kill		Didymo on rock from Connecticut River

How is Didymo a threat?

• In some conditions, Didymo can produce large amounts of stalk material with no nutritional value for insects.
• Stalk material breaks down very slowly, persists for a long time after the diatom dies and can create vast mats that can blanket the streambed.
• Mats may cause negative ecological, hydrologic, or aesthetic impacts.
• Mats may create significant biological impacts to stream ecosystem function, with the ability to alter the foodweb.
• Didymo has expanded its geographic range; a trait of invasive species.
• Negative economic impacts to tourism, fisheries, hydropower, and other uses are possible.
• Didymo cells can be easily spread on fishing gear, clothing, and other recreational, scientific or construction equipment that contacts the water.
• If we’re moving Didymo around, we may also be moving around other invasive species or fish diseases we can’t see.

"Worst case" Didymo scenario - New Zealand (photos courtesy of Biosecurity New Zealand) Click on right photo to enlarge (pdf, 63 KB)

What impacts will Didymo have on our natural resources?

• Didymo can alter aquatic insect and native algae populations.
• Extensive mats can reduce or exclude mayflies, caddisflies, and stoneflies: important trout food.  Chironomids (midges) and worms – less-preferred trout food – are likely to become more abundant in their place.
• Changes in aquatic insect communities could potentially impact fisheries but studies of Didymo’s impact on fisheries are inconclusive so far.
• Persistent stalk/mat material could reduce the availability of spawning habitat.
• There are ongoing studies on fish impacts in the U.S., Canada, and Europe.

What is the Vermont Agency of Natural Resources doing about Didymo?

• ANR is keeping current on national and international research pertaining to the biology and management of Didymo.
• ANR provides information to the public about how to reduce the spread of Didymo and other aquatic invasive species.
• ANR field staff have developed Best Management Practices and disinfection procedures for field activities to minimize the spread of both aquatic invasive species and pathogens in Vermont waters.
• ANR is evaluating and adjusting its hatchery stocking activities to address the threat of inadvertent spread of aquatic invasive species and fish and wildlife pathogens, including VHS.
• ANR and its partners have developed a poster (left) for placing at river access areas and in public locations to inform the public about Didymo spread prevention. (Click on image at right to obtain poster full size, pdf, 300 KB)

What precautions should everyone take to avoid spreading Didymo?

As recreational or professional users of Vermont’s aquatic resources, we all have the potential to spread aquatic invasive species and fish and wildlife pathogens from stream to stream and watershed to watershed.  Responsible stewards of our state waters take precautions to minimize the spread of these threats.

Follow these ‘Best Practices’ and Disinfection Procedures to minimize the spread of aquatic invasive species and fish and wildlife pathogens.  This approach is modeled after New Zealand’s widely-used ‘Check, Clean, Dry’ strategy.  While designed to address the spread of Didymo, these practices will help to minimize the spread of other aquatic invasive species and fish and wildlife pathogens as well.  

BEST PRACTICES for minimizing the spread of Didymo, other aquatic invasive species, and fish and wildlife pathogens while using Vermont’s waters:

• All Users - Disinfect your gear and boat before traveling between different bodies of water or watersheds (see below).
• All Users - If you move around to fish, boat, play or work, construct and use a simple, portable disinfection kit.
• All Users - When possible, fish, boat, play or work in a single waterbody in a single day, rather than traveling between multiple watersheds without appropriate precautions.
• All Users - Visually inspect your boat, gear and equipment before entering and leaving the water.  Remove all plants, plant fragments, animals, mud or other debris and discard in the trash. 
• Anglers - When practical, fish in a downstream direction.  This doesn’t mean you can’t wade upstream a bit to fish that nice run upstream – think on a watershed scale.  By fishing at the mouth of a large river in the morning, then going to the headwaters in the afternoon without disinfecting your gear, you’ve potentially spread Didymo upstream to the whole stream, which may not have been previously infected.  Most algae and aquatic invasives/pathogens can’t swim upstream.
• Anglers - Consider the use of easily disinfected wading gear.  For example, rubber-soled wading boots with cleats are easier to disinfect quickly than felt-soled boots.
• Anglers, Guides, Outfitters - Designate waders/boots/canoes/tubes for different watersheds or have multiple sets available for same-day travel, when needed.
• Canoeists, Kayakers, Boaters, Tubers - Remove drain plug and drain any water prior to leaving boat loading/unloading area.  Don’t move water between waterbodies.

How can I properly disinfect my recreational equipment?

DISINFECTION PROCEDURES – Disinfect prior to moving to another waterbody, watershed, or upstream site

There are a number of disinfection techniques that will kill most aquatic invasive species and fish and wildlife pathogens, including Didymo.  Solutions of bleach or dishwashing detergent products are suggested as they provide the best combination of availability, cost AND effectiveness against Didymo as well as other aquatic invasive species and fish and wildlife pathogens, such as whirling disease.  Choose the appropriate agent based on the actual items requiring disinfection (i.e. bleach solutions will destroy some items).  It is recommended that all disinfected equipment be rinsed on dry land, away from state waters.  It is preferable to drain used solutions into treated wastewater (e.g. pour down a sink drain).

Non-absorbent items (boats, canoes, rubber waders, ‘hard-sided’ objects)

• Dishwashing Detergent: soak and scrub for at least one minute in 5% solution (add 6.5oz of detergent with water to make one gallon).  ‘Green’ products are less effective and not recommended for disinfecting.
• Bleach: soak or spray all surfaces for at least one minute in 2% household bleach (2.5oz with water added to make one gallon).  Bleach solutions must be replaced daily to remain effective.
• Hot Water: soak for at least one minute in very hot water (above 140°F – hotter than most tap water) OR for at least 20 minutes in hot water kept above 120°F (hot tap water, uncomfortable to touch).
• Drying:  Drying will kill Didymo, but slightly moist environments will support some organisms for months.  This approach should only be used for gear that can be left in the sun for extended periods of time (i.e. a canoe that’s left in the yard for several days between uses).

Absorbent items require longer soaking times to allow thorough penetration into the materials.  Felt-soled waders, for example, are difficult and take time to properly disinfect. Other absorbent items include clothing, wetsuits, sandals with fabric straps, or anything else that takes time to dry out.  The thicker and denser a material, the longer it will require for adequate disinfection.  Err on the side of caution.  Bleach solutions are not recommended for absorbent materials. 

• Hot Water:  Soak items for at least 40 minutes in very hot water kept above 140°F (hotter than most tap water).
• Dishwashing Detergent and hot water: (‘Green’ products are less effective and not recommended for disinfecting):  soak for 30 minutes in a hot 5% detergent/water solution kept above 120°F.

A simple, portable DISINFECTION KIT might include:

• Large trash can and/or medium sized Rubbermaid-type bin for soaking wading boots
• Large stiff bristle brush for scrubbing
• Spray bottle(s) or herbicidal pump spray can(s)
• Graduated cylinder or measuring cup
• 5% detergent solution and/or 2% bleach Solution

What should I do if I think I’ve found Didymo?

• Refer to the ANR Didymo Identification Guide (pdf, 51 KB) to validate your suspicions.
• Collect a dime- to quarter-sized sample in a small container, zip-lock bag, or folded in a business card (a dry sample can be positively identified).
• If possible, obtain GPS coordinates or provide a clearly marked map indicating where the sample was collected, or provide a detailed description so that Agency personnel can return to the site for follow-up.
• Fill out a sample submission form (pdf, 23 KB).
• Mail sample, map if available, and sample submission form, to the address provided on the form.  ANR will confirm receipt of your sample by mail.

Where can I get more information on Didymo?

• EPA Region 8 web site on Didymosphenia geminata (you'll be leaving the VT ANR web site)
• NH/VT public web site on Didymo (you'll be leaving the VT ANR web site)
• Didymo - Cleaning Methods | MAF Biosecurity New Zealand (you'll be leaving the VT ANR web site)

Updated: May 2008