Didymo Algae Is Poised To Foul Southwest Pennsylvania's Trout Waters

By John Hayes / PittsburghPost-Gazette

OHIOPYLE, Pa. -- We were warned. For years biologists at universities, wildlife organizations and state agencies cautioned against the spread of "rock snot," the mucous-textured invasive algae that has disrupted watersheds throughout the American Northeast and Northwest.

The Youghiogheny River falls at Ohiopyle State Park,

Fayette County, is the point of impact where a dense,

gooey invasive algae has entered Western Pennsylvania.

In May an aquatic biologist with the Delaware River Basin Commission, on a family vacation to Ohiopyle, accidentally discovered didymo on rocks just below the historic falls on the Youghiogheny River in Fayette County. This month Philadelphia's Drexel University confirmed the first established didymo bloom in Western Pennsylvania.

"There was plenty of didymo on the rocks, so I had no trouble finding material to collect, and my sample was filled with nice, healthy, living didymo," wrote biologist Erik L. Silldorff, in his report to Drexel. "In terms of a risk of spread, I would say the Youghiogheny is now a potential launching pad, especially with the combined traffic of whitewater enthusiasts and trout anglers."

Didymo's regional arrival on the Youghiogheny was no surprise to some, but it is ironic. In 2008 the state Department of Conservation and Natural Resources designated the 132-mile waterway River of the Year.

Didymosphenia geminata algae is not harmful to humans. It is native to cold, fast-flowing rivers and streams with rocky bottoms -- typically trout waters -- in Northern Europe and Canada. In climates farther south, didymo grows out of control, spreading rapidly in a slippery brown-gray mat with long, grayish-white strands.

The algae can grow into dense blooms that fill the cavities between rocks, blocking sunlight and disrupting ecological processes resulting in a decline in plant and animal life. Macro-invertebrates, the primary food for trout, are generally affected first. As the algae carpets the waterway, the biomass is altered, impacting bait fish and game fish. The algae slips off rocks and permeates the water, making a gooey, unsatisfying mess for recreational anglers and boaters.

Didymo can grow from a single invisible cell. It spreads easily, carried on equipment used by boaters, anglers and industrial vehicles, as well on the legs of migrating waterfowl. The U.S. Department of Agriculture's National Invasive Species Information Center (www.invasivespeciesinfo.gov) reports that by 2004 didymo had spread to rivers of the Western United States. It was discovered east of the Mississippi River in Tennessee in 2005.

Maryland Department of Natural Resources confirmed didymo at Baltimore County's Gunpowder Falls in 2008, in Allegany County's lower Savage River in 2009 (about 65 miles from Ohiopyle), and on Frederick County's Big Hunting Creek weeks ago.

"The ecological impacts of didymo are still uncertain in Maryland waters," said DNR's Ron Klauda, a member of the agency's invasive species team, in a written statement, "but heavy blooms definitely cause problems for trout anglers."

In Pennsylvania during the last two months, Fish and Boat officials documented didymo blooms in the Delaware River as far south as Bucks County, and in Dyberry Creek in Wayne County, as well as in the Youghiogheny River.

The Ohiopyle bloom is located in the pool below the falls, a spot that is difficult for wading anglers to access but a popular launching point for kayakers."That area gets very little fishing pressure," said Dale Kotowski, a fly-fishing guide for Wilderness Voyageurs, an Ohiopyle outfitter since 1964. "I can't imagine the thousands of paddlers who come to that area, so it doesn't surprise me that's where didymo showed up first." Experts predict serious consequences for Western Pennsylvania trout anglers.

"It is almost impossible to predict the scope and extent of the spread of species invasions like this one," said John Arway, executive director of the state Fish and Boat Commission. "Humans aren't the only vectors [of its expansion] and the reality is that it will spread, but hopefully we can slow it down and it won't dominate our rivers."

It's too soon to tell how the presence of didymo will impact Youghiogheny trout stocking and native trout reproduction in the region. The waters downstream from Ohiopyle are clearly in jeopardy. Considering didymo's documented propensity to spread quickly, all of the popular trout waters of the Laurel Highlands are also at risk, including Meadow Run, the Casselman River and Laurel Hill, Dunbar, Dunlap, Jones Mill, Indian and Blue Hole creeks.

"I've fished on didymo from the White River in Arkansas to the Gunpowder in the Baltimore area," said Kotowski. "The Savage is absolutely covered with it -- rock snot from shore to shore. Every rock below the dam is covered, which makes walking virtually impossible. It's hard to fish anything subsurface -- the line, fly, everything picks up hunks of this stuff. On the Savage, that's happened in the span of a couple of years."

Dry fly fishing on stretches of the Savage was more productive, Kotowski said. The hatches had yet to be impacted by the constrictive algae. The falls area at Ohiopyle fished fine in late April, he said, and to date didymo has not been detected upstream on the 10-mile Middle Yough from Confluence to Ohiopyle.

While the spread of didymo probably can't be stopped, boaters and anglers may be able to slow its rate of expansion.

Maryland bans felt wading soles, which are believed to easily transport didymo cells among watersheds. The state's DNR places wader washing stations at popular fishing locations. Anglers are urged to clean mud and other debris from their boots, then step into pails of saltwater and brush toe to knee for about 60 seconds.

Felt soles remain legal in Pennsylvania. Fish and Boat officials have said the agency is reluctant to ban a product proven to improve water safety while more troubling modes of didymo transportation -- boats and industrial machinery -- remain unregulated from an invasive species perspective. The state does not provide wader washing stations.

For now, education remains the main tool in combating the spread of didymo. "We just need to be cautious as users of the river," said Arway, "and make sure we clean our gear so that we aren't responsible for spreading it around the watershed."

In a written statement, John Norbeck, DCNR director of state parks, said the discovery of didymo at Ohioppyle will not immediately impact park visitors. "The park encourages all boaters, fishermen and visitors to be vigilant and avoid spreading didymo into other rivers and streams by properly washing all gear, equipment and watercraft," he said.

The Mountain Watershed Association, a regional nonprofit conservation group, recommends disinfecting all fishing and boating gear used throughout the region in a solution of 10 percent household bleach and 90 percent water, or a strong salt solution, for at least 10 minutes. Extra care should be taken to soak porous materials such as nets, ropes, cloth items, water shoes and felt-soled waders and wading shoes.