As if the Bay watershed didn't have enough algae.

Maryland recently became the latest state to discover a new, invasive algal species that scientists fear will threaten trout streams and other high-quality waterways throughout the region.

The nonnative species, Didymosphenia geminata-commonly called Didymo-was found by anglers on the Gunpowder Falls in Baltimore County this spring. Follow-up surveys by biologists from the Maryland Department of Natural Resources found numerous patches of the stringy, brown algae covering rocks and stream bottom between Prettyboy Reservoir and Loch Raven Reservoir.

Most patches in the Gunpowder only cover a few yards of stream bottom. But in other locations, Didymo is known to completely smother large areas of stream bottom, choking out organisms that thrive in the normally stone-strewn substrate which provides food for trout and other fish.

State officials have responded by posting signs at access points along the river asking anglers, boaters and other water users to take added precautions.

They are also planning to set up "disinfection stations" along the river-tanks of salt water solution-where water users can soak their boots and gear to kill the algae after it comes out of the water.

"To my knowledge, nobody has been able to eradicate it when it has shown up," said Ron Klauda, director of DNR's Monitoring and Non-Tidal Assessment Division. "So we'd like to at least keep it confined to that river system."

The invasive species is known to exist in one other location within the Bay watershed, the Jackson River, a tributary to the James, where it was discovered in 2006. It's also been found in two Virginia rivers outside the Bay watershed, the Smith and the Pound. State agencies and conservation groups have launched educational efforts to help contain its spread.

Didymo forms long "stalks" of algae that combine to form heavy mats which smother a stream bottom. The mats, which can be white, yellow or brown, can persist for several months after the algae die, disturbing habitat for a protracted period of time.

The appearance of the algae has given rise to the common nickname of "rock snot." In part of New England, a "stop rock snot" radio campaign urges anglers and boaters to help prevent the spread of Didymo.

Didymo is a diatom, a larger form of algae that has a silica cell wall. As a result, although the mats appear slimy, they actually have a gritty feel which some describe as being similar to wet wool.

Didymo is native to far northern regions of the Northern Hemisphere, including North America, Asia and Europe. It's unusual in that it thrives in cool-water, fast-flowing, low-nutrient streams-conditions typical of high-quality trout streams. Gunpowder Falls, which has a reproducing brown trout population, is considered perhaps the best trout stream in Central Maryland.

Its appearance in popular trout streams also provides an easy means of transport to other waterways. Didymo cells-which may survive for several days in moist conditions-can hitch a ride on gear, bait buckets or wading boots. It can also spread on kayaks and other boats.

Its range has gradually been expanding over the last two decades, probably because of accidental transport by anglers. In recent years, it has been reported in several New England rivers, the upper tributaries of the Delaware River, several western states and mountainous parts of the Tennessee River, among others.

The algae has even turned up in New Zealand, where it has become a major nuisance in some areas.

"It reproduces asexually," Klauda said. "So literally, one cell can start a new colony." And once established, cells easily transport downstream. "You can see it break off in clumps even as you're just watching it."

Gunpowder Falls is the only known location for Didymo in Maryland, although Klauda said that the DNR will soon begin surveys in nearby streams to see if the alga has spread. Because of the river's proximity to Pennsylvania, it's also possible that Didymo could readily cross the state line.

Scientists can't predict exactly what the presence of Didymo will mean for the Gunpowder. "We're not really certain if the impacts are going to be disastrous or not," Klauda said. "It certainly hampers fishing when you've got this stuff."

But the algae's rapid expanse in recent years, coupled with its ability to dominate habitats, has raised concern around the world that it will have a significant impact on the biology of streams by altering the food web-in New Zealand, the failure to clean equipment after fishing in Didymo-infested waters can trigger steep fines.

Some work already suggests the trout avoid areas dominated by Didymo. As a result, it also threatens areas where trout fishing is a major source of tourism.

"We're hoping," Klauda said, "people don't take it out of the Gunpowder."

Help Stop Rock Snot

  • Avoid moving from one stream to another without taking precautions to clean equipment that came into contact with the water. Remove any clumps of algae or sediment.
  • At home, disinfect equipment by soaking it in a 5 percent salt solution (1 pound salt per 5 gallons water) for several minutes, or scrub with dish detergent and rinse well.
  • If disinfection is not possible, let equipment dry completely for at least 48 hours.
  • Replace felt bottom boots and waders with boots made of non-porous materials that are easier to clean.
  • If possible, consider having two sets of equipment in order to move safely from one spot to another.
  • The Maryland Department of Natural Resources urges anyone who observes Didymo to contact Don Cosden at 410-260-8287 as soon as possible.

- Maryland Department of Natural Resources