'Rock snot' invades Delaware

TUSTEN — It varies from ugly to uglier.

But the Didymo alga, otherwise known as "rock snot," is more than just an eyesore.

The recent discovery of blooms of the invasive species along a 100-mile stretch of the Delaware River has set in motion a vigorous outreach campaign.

Alarmed scientists and river advocates are mobilizing to prevent boaters and anglers from spreading a nuisance they worry could threaten the natural balance of the river, its tributaries and other waterways in the area.

"In this part of the river, this is the first time it's been found in this abundance," said Erik Silldorff, an aquatic biologist with the Delaware River Basin Commission. "The risk is that you can disrupt the entire ecology of the system."

The mucous-like Didymo thrives in cold water and is easily spread via fishing equipment and shoe soles. It clings to rocks and river bottoms, overrunning the natural habitats for the native algae and insects that feed fish.

It was Silldorff who discovered large blooms of rock snot April 18 in a 40-mile area bounded by the Lackawaxen River and the Dingmans Ferry Bridge, located at river-mile 239.

Scientists from the National Park Service and Pennsylvania's Department of Environmental Protection found blooms as far north as river-mile 330, in the area of the Delaware's East and West branches.

Summer warming limits growth downstream, Silldorff said. But the discovery of high concentrations of rock snot below Callicoon is sparking fears of greater transmission to the watershed's colder waters, especially those nurturing trout and other fish.

"The risk is much greater on a river like the East Branch or the Neversink, where Didymo could bloom year-round and cause major problems," Silldorff said.

The National Park Service has been posting information about the dangers of rock snot at access points along the river.

It has also been contacting fishing guides, and plans to spread the word among canoe and kayak businesses," said Don Hamilton, a natural-resource specialist and biologist with the Park Service.

"There are protocols for people to clean their waders and wading shoes," Hamilton said.

A grant is also funding research by the Park Service into the biology of Didymo, Hamilton said. Scientists are particularly concerned about rock snot's spread into areas where it has previously been nonexistent.

"It's being seen in areas where it didn't seem to be noticed," Hamilton said. "And it's persisting for a very long time."

lsparks@th-record.com