Anthony Depalma, The New York Times 15 Jun 09;
SHANDAKEN, N.Y. — The Esopus Creek, a legendary Catskill Mountain fly fishing stream that is an integral part of New York City’s vast upstate drinking water system, is one of the latest bodies of water to be infected with Didymosphenia geminata, a fast-spreading single-cell algae that is better known to fishermen and biologists around the world as rock snot.
Although officials had been on the lookout for spreading Didymo, as it is also called, since it was first confirmed in New York two years ago, they had not found it in the Esopus when they canvassed the area last fall. A fly fisherman told state biologists a few weeks ago that he thought he had seen the telltale gray tendrils of Didymo clinging to rocks on the bed of the Esopus here, about 120 miles northwest of Manhattan.
Investigators later confirmed that Didymo had spread along 12 miles of the Esopus from Shandaken to the Ashokan Reservoir. Biologists believe it is being transported by sport fishermen.
Didymo has a natural tendency to grow upstream in fast-moving rivers and creeks, but it can spread by clinging to fishing equipment, especially the felt-bottom waders that fly fishermen use to keep from slipping on river bottoms.
Didymo is considered native to parts of North America, where it was found in higher elevations with cold, nutrient-poor waters. But in the last 20 years, the single-celled diatom seems to have morphed into a more aggressive invasive species, spreading from British Columbia across the continent to New York.
Unlike other algae, which float on the surface, Didymo clings to rocks on the bottom of rivers, streams and lakes. At times it grows furiously in blooms that can cover a river bottom from bank to bank, smothering the stone flies, worms and other organisms that trout and other sport fish live on.
Didymo is not considered harmful to human health, but it can grow in mats so thick that they clog water intakes. And it is not called rock snot for nothing. It grows in long gooey tan, gray and brown masses that resemble wet toilet tissue or sludge. Despite its repulsive appearance, it is not slimy to the touch. Rather, it feels like wet cotton and does not break apart easily.
Didymo caught biologists’ attention in 2004 when it was discovered on South Island in New Zealand. There was no previous record of it in the Southern Hemisphere. But since being found there, it has spread to more than 120 rivers and streams on South Island. Blooms there have severely reduced fish populations and turned wild streams into sludge pits.
Scientists believe that a fisherman from North America who packed his damp waders in a bag might have flown to a remote stream in New Zealand with the tenacious Didymo piggybacking on his boots. Once back in water, it made itself at home.
In an effort to keep it from spreading to the North Island, Fish and Game New Zealand has banned the use of felt-sole waders and made it a crime punishable by up to five years in prison for anyone to knowingly transport Didymo from one stream to another.
In the United States, the Environmental Protection Agency considers rock snot an invasive species, as do several states, although none have gone so far as to ban felt-soled waders. However, manufacturers have developed rubber-sole alternatives that have become increasingly popular with fly fishermen.
Sarah A. Spaulding, an ecologist with the United States Geological Survey in Boulder, Colo., who has studied Didymo extensively, said that among the traits of the microorganism is its ability to survive outside water for a day or more, making it easy for anglers to transport it as they move from river to river.
Even more worrisome, when kept in a cool, damp place — like the trunk of a car — Didymo can survive for 90 days in a felt sole, Dr. Spaulding said.
Didymo presents other mysteries. Its destructive blooms are not set off by excess nutrients in the water — often from human byproducts — the way other algae booms are. Didymo can bloom in waters that are nearly pristine.
Dr. Spaulding said that not enough was known about Didymo to say whether its recent geographic spread and more aggressive behavior were caused by environmental changes or genetic mutations, or were simply part of a natural cycle that had never been observed.
Biologists theorize that free-flowing streams are less habitable for Didymo than controlled waters connected to reservoirs because they are regularly scoured clean by raging floodwaters.
Didymo has been found in the waters of the Tennessee Valley Authority and in California. Michael J. Flaherty, regional fisheries director of the New York State Department of Environmental Conservation, said Didymo had been found on the east and west branches of the Delaware River, the location of two huge reservoirs in the New York City water system. The Esopus Creek also receives water from a New York City reservoir. And Mr. Flaherty said he was worried that Didymo could spread to two of the most famous fly fishing streams in the country, the Beaverkill and the Willowemoc, which are close to the Delaware’s tributaries.
Leslie J. Surprenant, the New York State invasive species management coordinator, said there were no known ways to eradicate Didymo once it was established. The best that can be hoped for, she said, is to slow its spread by informing fishermen and others who use the infected streams.
Local fishing clubs have said the state has not been aggressive enough about posting warning signs at popular fishing access areas and distributing information about rock snot.
On its Web site, New York encourages fishermen to submerge waders in a solution of water and bleach to kill cells before they can spread.
Ms. Surprenant said Didymo was just one invasive species that could be transported by fishermen. Others include the whirling disease parasite, which affects certain species of fish. She said Didymo’s cringe-inducing common name — rock snot — had been helpful because it made fishermen take notice. In a sense, it has become a signature species — one ecologist called it a poster child for what could go wrong in a stream — and by focusing on changing anglers’ behavior to prevent Didymo from spreading, the state can slow the spread of other invasive species.
The message is starting to get out, at least to some groups. Alfred Marchetti, a retired chemist who was out fishing with friends on the Esopus recently, did not know the name Didymo but said he knew all about how dangerous rock snot could be. He and his friends were on a “five rivers in five days” fishing trip in the Catskills, and they said they were dunking their waders in a washtub filled with water and bleach as soon as they got back to camp.
The Federation of Fly Fishers, a national organization, discourages the use of bleach because it could contaminate streams and because its use may give anglers a false sense of confidence that a quick dip can kill all Didymo cells. Instead, the group urges fishermen to “check, clean and dry,” inspecting gear for signs of Didymo, cleaning boots and lines before leaving infected streams, and allowing everything to dry thoroughly before fishing another spot.
