Tim Daley/ Pennsylvania Department of Environmental Protection
Didymo or rock snot is an invasive algae that has recently been discovered in the southwestern part of Pennsylvania. The algae was found in the Youghiogheny River (although this photo was not taken there).
By Don Hopey Pittsburgh Post-Gazette
The Yough has "rock snot," a slimy, invasive alga that's even worse than it sounds because it can thickly coat riverbeds and kill native fish, freshwater mussels and aquatic insects.
And the slimy green tendrils aren't much fun to swim in or boat through either, and that could affect recreational pursuits on the Youghiogheny River, a heavily used whitewater boating and fishing flow in Fayette County.
An aquatic biologist with the Delaware River Basin Commission, Erik Silldorff, found the alga, also commonly known as didymo, last month on large boulders in Ohiopyle State Park.
Mr. Silldorff, who has done extensive work with the alga in the Delaware, was on a family vacation when he stopped for a swim and noticed what for him was familiar looking alga. He took a sample and the finding was confirmed June 1 by the Academy of Natural Sciences.
"We are very concerned," Pennsylvania Fish and Boat Commission executive director John Arway said. "Didymo can blanket a riverbed and fill in spaces between rocks used by other species."
He said when didymo fills in all the nooks and crannies on a riverbed it disrupts the "aquatic food chain pyramid" displacing aquatic insects, crayfish and freshwater mussels that are food sources for many fish species.
Beverly Braverman, executive director of the Mountain Watershed Association, said the discovery of didymo is like a horror movie for the river.
"It's like 'The Blob,' where this creepy thing grew from a single cell and kept growing and growing," she said. "It's scary. This will have a huge impact and no one knows how to stop it."
Native to cooler regions of Europe, Asia and North America, didymosphenia geminata has been discovered in an ever widening range over the past few decades and is now found in 11 states, including New York and West Virginia.
Didymo was discovered in the upper Delaware River in 2007 and later in Dyberry Creek in Wayne County.
Earlier this month state and federal aquatic biologists for the first time found dense "blooms" of rock snot in the middle Delaware, past its confluence with the Lehigh River, as far south as Bucks County.
Didymo spores have also been found in the Delaware as far down river as Trenton, New Jersey.
"We may not be able to eliminate didymo from an infected waterway, but we can do our best to slow its spread and to prevent it from spreading to other waters," Bob Morgan, a fish commission ecologist who studies aquatic invasive species, said.
He said didymo cells can easily be carried downstream and picked up by any equipment contacting the infected water, including fishing tackle, waders, recreational equipment, and 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," Mr. Morgan said.