Photo-Chesapeake Bay Program

Where are they from?

From cool waters across the Eurasia continent, it is also native to North America. However, this algae has been found to tolerate new water chemistry, this has made it more aggressive, leading to introduction in Pennsylvania waterways.

Why is it so harmful?

Didymo, also know as Rock Snot, is easily transmissible to other streams as it can live on boots, fishing gear, and boats for up to 40 days without water. During large blooms didymo create enormous amounts of stalky material that forms mats on the river or stream bed. These can completely cover the stream bottom and choke out native plant and algae species as well as reduce food availability for fish and macro-organisms. The look of didymo is quite unappealing, which if tourism spots are affected, can lead to decreased economic value of these areas.

How can I identify this?

Young blooms of this algae look like pimples or raised areas on river rocks. During nuisance blooms or large blooming events, they form long, thick mats that are gray or brown in color. Didymo has the texture of wet wool, and is not slimy like other algae.

Where can I learn more?

Pennsylvania Sea Grant-- https://seagrant.psu.edu/file/413/download?token=BU23K-U3

DCNR--http://elibrary.dcnr.pa.gov/PDFProvider.ashx?action=PDFStream&docID=1738741&chksum=&revision=0&docName=Didymo&nativeExt=pdf&PromptToSave=False&Size=156685&ViewerMode=2&overlay=0