Check out the Maryland State YouTube Channel Follow us  on Twitter Folllow us on Facebook Email Us DNR Home

Didymo Infests Third Maryland Trout Stream

DNR urges anglers to help stop its spread

Annapolis, Md. (May 7, 2012) — Maryland Department of Natural Resources’ (DNR) biologists confirmed the presence of didymo, an invasive algae known to anglers as rock snot or boulder boogers, in Big Hunting Creek in Frederick County.

“We observed the heaviest growth of didymo at the Joe Brooks Memorial, with lighter growth areas downstream to just below the canyon,” said John Mullican, DNR’s Regional Fisheries Manager for the County. “We didn’t see any didymo growth above or below Frank Bentz Pond or upstream from the Joe Brooks Memorial, and no didymo in Little Hunting Creek.”

Maryland biologists first confirmed didymo in Gunpowder Falls in Baltimore County in early 2008. In 2009, it turned up in the lower Savage River Allegany County. Although didymo presence was suspected in Big Hunting Creek in 2011, it was not confirmed until this spring.

Didymo prefers the cold, fast-flowing waters and rocky substrates found in good trout streams. Once it takes hold, didymo can bloom and cover the entire stream bottom from bank to bank with a brownish-gray mat that grows long, grayish-white strands, resembling dreadlocks.

“The ecological impacts of didymo are still uncertain in Maryland waters,” said Ron Klauda, a member of DNR’s invasive species team who’s been surveying didymo abundance and distribution in the Gunpowder for nearly four years, “but heavy blooms definitely cause problems for trout anglers.”

For a video by citizen Jason du Pont chronicling didymo on the Gunpowder, visit

DNR urges all anglers to do their part in helping to stop the spread of didymo to other trout waters. Anglers should remove mud and debris from their boots before entering and soon after leaving streams and use wader wash stations to clean their boots in saltwater (from the soles to the knee) before heading off to another body of water. If a wader wash station isn’t available or the wash pan of salt water is empty, anglers should disinfect their boots at home. Letting boots and gear dry thoroughly for at least 5 days between fishing trip will also kill didymo cells. DNR also reminds anglers that felt-soled boots were banned in all Maryland waters effective March 22, 2011, to protect and preserve wildlife and their habitats. DNR appreciates the public’s help in controlling didymo and other invasive species.

   May 7, 2012

Contact: Josh Davidsburg
410-260-8002 office I 410-507-7526 cell

The Maryland Department of Natural Resources is the state agency responsible for providing natural and living resource-related services to citizens and visitors. DNR manages nearly one-half million acres of public lands and 17,000 miles of waterways, along with Maryland's forests, fisheries and wildlife for maximum environmental, economic and quality of life benefits. A national leader in land conservation, DNR-managed parks and natural, historic and cultural resources attract 11 million visitors annually. DNR is the lead agency in Maryland's effort to restore the Chesapeake Bay, the state's number one environmental priority. DNR is the lead agency in Maryland's effort to restore the Chesapeake Bay, the state's number one environmental priority. Learn more at