WEST TRENTON, NJ — A staff scientist at the Delaware River Basin Commission (DRBC) has found extensive mats of the aquatic alga Didymosphenia geminata (also known as didymo or “rock snot”), an invasive species, in the Delaware River.

Dr. Erik Silldorff, an aquatic biologist with the commission, discovered large didymo blooms in the Delaware River over a 40-mile stretch extending from the area near the confluence with the Lackawaxen River downstream to the vicinity of Dingmans Ferry Bridge.

Didymo covers rock surfaces in cold, moderate to fast flowing water. Since 2007, it has been found at low concentrations during the summer months from around Hancock, NY downstream to the area around Dingmans Ferry, PA, with high-density patches frequently observed in the cold-water zones of the East and West branches of the Delaware River, as well as in the colder zones of the upper main stem river.

The extent and intensity of the newly discovered blooms, however is considered alarming. In addition, scientists with the National Park Service and the Pennsylvania Department of Environmental Protection over this past week independently documented didymo blooms extending north of the area discovered by Silldorff to Callicoon, NY as well as from Long Eddy, NY upstream into the East and West branches of the Delaware River. The observed intensity of these patches was variable.

While didymo is not a public health hazard, there is great ecological concern with discovering the invasive alga to this extent and in these concentrations. Thick mats of didymo can crowd out or smother more biologically valuable algae growing on the riverbed, thereby significantly altering the physical and biological conditions within a stream.

Didymo can easily attach to fishing equipment, especially felt-soled boots, and other equipment or vessels exposed to the water. DRBC staff is coordinating with scientists from Pennsylvania, New York, New Jersey and the National Park Service to quickly alert the public and identify appropriate next steps. Visit www.drbc.net.