Back in 2011 Didymo was first reported to the public on the Farmington River. Also known as ‘Rock Snot’, this invasive algae can be detrimental to a river’s ecosystem for several reasons. Extensive blooms can actually cover the river bottom for several miles and smoother native plants and insects, affecting the whole food chain. Didymo has a negative impact on recreation too. Because the food chain is changed, trout populations are affected. Lures can become entangled. Rocks become slippery to walk on, and the esthetic beauty of the river is lessened.



Humans are the main cause of the spread of didymo, which likes to attach itself to waders or the bottom of boats. How can you help stop the spread? This is from the PA Fish and Boat Commission website:


CHECK -- Before you leave a river, stream, or lake, check items and leave debris at site. If you find any later, treat and put in trash. Do not wash down drains.


CLEAN -- There are several ways to kill didymo. Choose the most practical treatment for your situation which will not adversely affect your gear.


Non-absorbent items


  • Detergent -- soak or spray all surfaces for at least one minute in 5% dishwashing detergent or (2 cups (16 oz.) or 500mls with water added to make 2.5 gal. or 10 liters); OR
  • Hot water -- soak for at least one minute in very hot water kept above 140° F (60° C) (hotter than most tap water) or for at least 20 minutes in hot water kept above 113° F (45° C) (uncomfortable to touch).


Absorbent items -- require longer soaking times to allow thorough saturation. For example, felt-soled waders require:


  • Hot water -- soak for at least 40 minutes in hot water kept above 113° F (45° C) ; OR
  • Hot water plus detergent -- soak for 30 minutes in hot water kept above 113° F (45° C) containing 5% dishwashing detergent; OR
  • Freezing any item until solid will also kill didymo.


DRY -- Drying will kill didymo, but slightly moist didymo can survive for months. To ensure didymo cells are dead by drying, the item must be completely dry to the touch, inside and out, then left dry for at least another 48 hours before use. If cleaning or drying is not practical, restrict equipment to a single waterway.

NOTE: The thicker and denser the material, the better it will be at holding moisture (and live cells), the slower it will be to dry out and the more difficult it will be to soak completely with cleaning solutions.


When cleaning equipment, we recommend that you


  • soak porous materials for longer than the specified times to ensure saturation with cleaning solution
  • choose a decontamination solution that will not adversely affect your equipment
  • follow manufacturer’s safety instructions when using products
  • dispose of cleaning waste well away from waterways


For Boats


  • Inspect every inch of your boat, trailer, and equipment – the hull, drive unit, trim plates, props, anchor, centerboards, paddles, wheels, hitch, chassis, etc. – and remove aquatic plants, animals, and mud from the boat, trailer and equipment before leaving any body of water;
  • Drain any and all water from your boat and equipment on land before leaving the area;
  • Do the following when away from direct drainage areas to lakes or rivers:
    -- Dump any leftover bait on land, especially if the live aquatic bait has been in contact with potentially infested waters.
    -- Disinfect live wells and bait wells, bilges, cooling systems, hulls, and decks with a 1:9 solution of household bleach and water allowing at least 10 minutes contact time. Rinse well to remove all residual chlorine. An easy recipe is a half-gallon of bleach into a 5 gallon bucket then fill with water (or a quart of bleach to a half bucket).
  • Rinse your boat after use, preferably with hot water. If hot water is not available use tap water and then allow at least five days to become completely dry before entering a new water body.
  • Do not transport any LIVE FISH, BAIT, OTHER CRITTERS, PLANTS, OR WATER from one body of water to another.

Here is some information from CT DEEP on Didymo that may be helpful: