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  • TBO Staff

Invasive Species Known As "Rock Snot" Making Moves

With the recent confirmation of the aquatic invasive alga didymo Didymosphenia geminata, also known as "rock snot," in Quemahoning Creek, Somerset County, the Pennsylvania Fish and Boat Commission (PFBC) and Department of Environmental Protection (PA DEP) are reminding anglers and boaters that cleaning their gear is the easiest, most effective means to prevent its spread to other waters.

Recently, state officials discovered didymo in Quemahoning Creek downstream of the Quemahoning Reservoir. Didymo does not present a public health hazard, but it can cause ecological damage by smothering other organisms which also live on the riverbed and support the food web for the resident fish community. It's been called "rock snot" because of its appearance. When squeezed dry, the alga, which is generally tan to beige in color, has the feel of moist cotton or wool.

“We may not be able to eliminate didymo from infected waterways, but there are things we can do to slow or prevent its spread to other waters,” said Heather Smiles, Chief of the PFBC’s Division of Environmental Services.

Didymo cells can easily be carried downstream and can be picked up by any items or equipment in contact with infected water including fishing tackle, waders, recreational equipment, boats, and trailers. It takes only one live didymo cell to start a new colony of the alga. We urge anglers and boaters to clean your gear before leaving a water body and entering another one.

Photo courtesy: Tim Daley, PA DEP

The PFBC recommends that anglers allow exposed equipment to completely dry before entering new waters. After equipment is dry to the touch, allow to dry another 48 hours. Thick and dense material such as life jackets or felt-soled wading gear will hold moisture longer, take longer to dry, and can be more difficult to clean.

Soaking equipment in hot water containing dishwashing detergent (2 cups of detergent for every 2.5 gallons of water) for 20 minutes or more also will kill didymo and some other AIS. If hot water is not available, a commercial hot-water car wash also makes a good location to wash boats, motors, and trailers. At the other end of the temperature range, freezing items solid for at least 24 hours is effective. If cleaning, drying, or freezing is not practical, please restrict the equipment's use to a single waterway.

“This section of Quemahoning Creek provides fishing opportunities for stocked trout as well as warm-water and cool-water fish. The PFBC annually stocks fingerling Brown Trout and Rainbow Trout in Quemahoning Creek downstream of the Quemahoning Reservoir,” said Gary Smith, Fisheries Biologist with the PFBC’s Fisheries Management Area 8.

Prior to detecting didymo in Quemahoning Creek, these blooms have been increasingly observed in Pennsylvania. Since 2007, didymo has been detected in the West Branch and main stem of the Delaware River, in Dyberry Creek in Wayne County, in the Youghiogheny River watershed in Fayette County, and in Pine Creek in Lycoming County.

For more details on how to stop the spread of didymo, visit

For more information on how to clean your gear, visit

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