The Yough has got "rock snot," a slimy, invasive alga that's even worse than it sounds because it can thickly coat and smother riverbeds, decimating native fish, freshwater mussels and aquatic insect populations.
And the slimy brown-green tendrils aren't much fun to swim in or boat through, either. That high yuck factor could eventually affect recreational pursuits on the Youghiogheny River, a heavily used white-water flow in Fayette County.
The alga, also commonly known as didymo, was discovered last month on large boulders in Ohiopyle State Park by Erik Silldorff, an aquatic biologist with the Delaware River Basin Commission.
Mr. Silldorff, a didymo expert who has done extensive work with the alga in the Delaware River, was on a family vacation when he stopped by the park for a swim and noticed what for him was a familiar-looking aquatic plant. He took a sample, and the finding was confirmed by the Academy of Natural Sciences at Drexel University in Philadelphia on June 1.
"We are very concerned," said John Arway, Pennsylvania Fish & Boat Commission executive director. "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.
The alga prefers big rocky river bottoms and, once introduced into a water body, is impossible to eradicate in an ecologically safe way. It can form mats of vegetation from 3 to 8 inches thick, significantly altering the physical and biological conditions of a river or stream.
Native to cooler regions of Europe, Asia and North America, didymosphenia geminata was originally found in cold, nutrient-poor rivers but has been discovered in an ever widening range of rivers, creeks and streams over the past few decades in 11 states, including New York and West Virginia.
Didymo has "hitchhiked" from waterway to waterway on fishing and boating equipment, and federal research is under way to determine if its spread has been facilitated by a mutant form of the alga.
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. It's scary. This will have a huge impact, and no one knows how to stop it."
Didymo was discovered in the upper Delaware River in 2007, and there was a bloom this year 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 downriver as Trenton, N.J.
The discovery of didymo in the Youghiogheny was the first in the western end of the state.
Didymo is not a public health hazard, and Bureau of State Parks director John Norbeck emphasized that it has not affected boating or fishing at Ohiopyle State Park.
"The Youghiogheny River at Ohiopyle State Park provides some of the best white-water boating and water-based recreation in the eastern United States," Mr. Norbeck said. "The discovery of didymo has no immediate impact to the visitor experience on or along the 'Yough.' Didymo is not considered a significant risk to human health."
State Park officers are working with the Fish & Boat Commission and the state Department of Environmental Protection to survey and monitor didymo growth in the river, and by next weekend will mount an aggressive and proactive informational campaign for boaters and fishermen.
"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," said Bob Morgan, a fish commission ecologist who studies aquatic invasive species.
He said didymo cells, invisible to the naked eye, 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.
"Containment is critical," Mr. Morgan said. "We urge anglers and boaters to clean your gear before leaving a water body and entering another one."
The Fish & Boat Commission recommends disinfecting boats, trailers, fishing gear and boots before entering any river or stream with a 5 percent solution of dishwashing detergent, or a 2 percent solution of bleach, or soaking surfaces for at least one minute with very hot water. Boaters and fishermen are also advised not to transport any live fish, bait or plants or water from one body of water to another.
Drying equipment before entering another water body will also kill didymo spores, but slightly moist didymo spores can survive for months out of the water.
Don Hopey: email@example.com or 412-263-1983. First Published June 12, 2012 4:00 AM