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Didymo (Invasive Freshwater Algae) in Virginia

Didymosphenia geminata, also known as “didymo,” is a single-celled algae that is firmly established in at least three rivers below dams in Virginia: the Smith River, the Jackson River, and the Pound River. Didymo is a non-toxic diatom that has the ability to colonize into long stalks and to cover entire river bottoms. Further, didymo has also gained an ignominious nickname, rock snot, because it can break off into large pieces and drape over streamside vegetation. Anglers have become frustrated with this import because it can entangle lines and hooks, ruining a day on the water.

Didymo’s native home is the Faroe Islands off of Scotland, and probably arrived in Virginia on the boots of a fisherman. It thrives in cold, clear, shallow water, just like the conditions found in our three major trout tailwaters. Didymo was “discovered” in each of these rivers during the summer of 2006 by anglers and biologists.

Efforts by the Department of Wildlife Resources and the Forest Service to monitor the amount and the distribution of this nuisance have begun. Other stakeholders, including Trout Unlimited and the Department of Conservation and Recreation, have begun an educational campaign in the Commonwealth to raise river-user awareness of didymo’s potential harm.

Posters (PDF), cards, fishing regulations, and websites are warning boaters and anglers to remove any algae fragments from their gear, to dry their gear completely, and to treat their gear with a dilute bleach solution to prevent the spread of this to other trout streams. Biologists world-wide are studying the short and long-term effects of didymo on freshwater fisheries, but it is still unknown how it will impact aquatic communities or if it can adapt to warmer environments. What we do know is that it is an aggravating nuisance, an economic detriment, and that it is here to stay.

Video: Didymo Alert – Jackson River, Lake Moomaw Tailwaters, Alleghany County, Virginia