BY JOHN RICHARDSON

MaineToday Media, Inc.

As anglers return to the state's streams and rivers this spring in search of prized trout, Maine officials will be watching for something else: a fast-spreading algae called "rock snot" that's fouling some of the world's pristine trout streams.

Rock snot, also commonly called didymo, is an invasive species that appears to hitch rides from one river to another on boots or waders worn by fishermen.

Once introduced to a new stream that has clean, fast-moving water, didymo can spread quickly and coat the rocky bottom with thick, gooey brown mats of algae.

There is no known way to get rid of it, and experts say it can disrupt river food webs and threaten valuable recreational fisheries.

Didymo may have originated in Scotland but has spread around the globe. It is a costly problem in New Zealand, where transporting it may be punishable by a fine and jail time, and is a major nuisance in western U.S. states and in Atlantic Canada.

It was first discovered in New England last summer when it invaded a stretch of the Connecticut River between northern New Hampshire and northern Vermont. Officials fear that Maine could be next.

"The thing about Didymo is it follows people and ends up in pristine fishing areas," said Paul Gregory, an invasive species specialist with the Maine Department of Environmental Protection. "It's the fishermen who are seeking out pristine trout waters. ... They're likely to be coming to Maine as well."

Although fly-fishing rivers have been the hardest hit, fishermen aren't the only possible modes of transportation. Boats, kayaks and canoes also can spread the algae if not cleaned properly, according to experts.

Maine officials began warning fishermen and boaters last fall by posting "Stop Rock Snot" signs next to some rivers urging fishermen and boaters to thoroughly clean and dry equipment between uses.

And they plan to increase monitoring and educational efforts again as the fishing season that begins April 1 heats up this spring.

Maine's DEP is concerned enough about the risk of spreading didymo that employees who wade through streams this summer as part of biological monitoring programs will use boots that don't have felt soles.

Felt soles are better for grabbing underwater rocks and preventing slips and falls. But they also are more difficult to clean and dry. Moist surfaces can keep the algae alive for up to two weeks.

Gregory said DEP staff will be more diligent in cleaning boots and will use rubber-soled waders whenever it won't be too dangerous. "If anybody's a good candidates for spreading it, it's us," he said.

Some fishermen also are taking the threat seriously.

"There's a lot more interest now in boots that don't have felt soles," said Jim Bernstein, manager at Eldredge Brothers Fly Shop in Cape Neddick and a fly fisherman. Anglers are coming in to buy studded boots that provide stability but are easier to keep clean, he said.

"For a lot of people who are really conscious about it, you make a mixture of water and bleach in a spray bottle and spray down your gear when you're done. The problem with that is you don't want to have bleach residue on your boots either," Bernstein said.

Officials in Maine and New Hampshire recommend soaking boots in hot tap water and soap or detergent for 30 minutes and thoroughly drying them before the next use.

Much is unknown about didymo, including what damage -- ecologically or economically -- it might do and how to get rid of it once it appears.

"It's ecological impacts are unclear," Brautigam said. "But I would expect because it's so aggressive and so dominating, it probably does have impacts ...on the suitability for fish habitat and on dissolved oxygen. It's basically another critter that's occupying limited space and resources that could be supporting natural flora and fauna."

State officials fear Didymo could become the river equivalent of milfoil, an invasive plant that is fouling lakes around the sate and can be spread on boat hulls and motors.

It is one of many invasive plants or animals that could reach Maine at any time and cause problems, according to Brautigam.

The spiny water flea, for example, has spread to the Great Lakes could have a big, if less visible, impact on aquatic communities here, he said.

"We could throw up signs every other week on something new," he said. "It's one of those things that everybody nowadays has to be thinking about, because we're so mobile."

Didymo's first casualty is usually the pristine appearance of a trout stream.

"Aesthetically, the problem is obvious. It changes the actual appearance of our streams. Tourist dollars are in the mix. It could be a significant hit," said Amy Smagula, invasive species specialist for the N.H. Department of Environmental Services.

Smagula said she's afraid the algae is already more widespread than people realize in the Northeast. "I think the more we look, the more we'll find it. I think we've got ample habitat for it."

Fishermen seem to be most concerned about the long-term effect on trout populations, according to Bernstein.

"It's pretty tough to stop the fishermen, but if it's killing off the food for the trout, then there's no trout and no reason to fish," he said. "From what I hear, it just takes a lot of the oxygen out of the water and it smothers the bottom. ... No one wants to be responsible for doing that."

Unfortunately, he said, it may be just a matter of time.

Bernstein is one of a small number of fly fishermen who fish year-round in a limited number of coastal rivers that stay open. For most angler, however, the season starts next week.

"It only takes one person," Bernstein said. "April first, there will be guys out all over the place. It's tradition."