Protect Park Streams from Rock Snot

Didymo, brown, wool like algae, held in hand.
Didymo has been found in streams in 16 states, including Tennessee. Do not be responsible for spreading Didymo to park streams.

Sarah Spaulding, USGS


Didymo (Didymosphenia geminata) or "rock snot" is an invasive single-celled algae species that smothers stream and riverbeds with mats of algae up to 8 inches thick. Historically, the range of Didymo was in the northern edges of North America, Europe and Asia, and considered very rare. Today, scientists have found that Didymo is able to adapt to new conditions, such as warmer water, resulting in Didymo being discovered in the streams of 16 states, including Tennessee.

Didymo occurs at a higher frequency in a controlled and regulated environment, such as in cold-water tailwaters below dams. In fact, Didymo has been found in every tailwater in East Tennessee, including Watauga, South Holston and the Noris and Cherokee Dams on the Tennessee River. Didymo can also thrive in cool, clear water environments like the streams found in the park.

Didymo is spread accidentally on fishing equipment like waders, boots, and fishing line in addition to recreation equipment such as boats, life jackets and inner tubes. Do not be responsible for spreading Didymo to park streams! For more information on area waters that tested positive and negative for Didymo,click here.

Learn more about the recent research concerning the presence and absence of Didymo in the region as well as treatment techniques being tested against the "rock snot".

Man fly fishing in river in park
Fisherman can accidentally spread Didymo. Make sure you clean all your gear and equipment before visiting.

Steve Head

Didymo cells cling to gear and equipment and can be transferred to new uncontaminated streams. These microscopic cells can remain alive for several days in a moist environment. Only one cell is needed to invade park streams. Once a Didymo cells contaminates a stream, it attaches itself firmly to the streambed and develops a stalk. The end of the stalk produces adhesive pads, which forms a thick mat that smothers the streambed.

Identify Didymo by:
1.Color: brown, tan or white (not green); may have long white "tails"
2.Texture: feels like wool or cotton (not slimy)
3.Strength: has stalks firmly attached to rocks

Didymo mats can completely cover long stretches of streambed, blocking sunlight from reaching native plants and fish. Didymo threatens aquatic habitats and biodiversity of the stream, killing native plants and fish by limiting sunlight.

Do not assume a stream or river is free from the infestation of Didymo.

To Prevent the Spread of Didymo:

1.Before coming to the park, clean all gear and equipment by:
• REMOVING debris and strands of alga from your gear
• CLEANING all gear in 2.5-5.0% solution of household bleach and hot water for 10 minutes. Hard to remove debris should be scrubbed with a biodegradable detergent.
• DRYING all gear to touch, and then continue drying time for at least 48 more hours.
2.Use only clean, thoroughly dried gear and equipment
3.Report sightings of suspect algae to Great Smoky Mountains National Park staff


Last updated: January 7, 2020

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