STOCKBRIDGE, Vt. (AP) – With steep banks, deep pools and pebbly shores this scenic stretch of the White River has long been a haven for fishing, swimming and floating on inner tubes. But biologists fear that an invasive algae known as “rock snot” could drive away swimmers and fish.

“I think if it takes hold, if it forms these massive blooms, it will really change the face of White River as we know it,” said Mary Russ, executive director of the White River Partnership.

The aquatic algae didymo — Didymosphenia geminata – has infested rivers in New Zealand with gray floating growth but had never been seen in the Northeast before this summer when fishermen spotted it in the upper Connecticut and White rivers.

Northeast states are on alert. They’re warning anglers and boaters to scour their boats and clean their gear to prevent the algae’s spread.

“Please don’t take chances, disinfect your fishing gear,” said Scott Decker, program supervisor with the New Hampshire Fish and Game Department.

That’s the only weapon against didymo, which is thought to have been spread by fishermen whose gear is absorbent or other recreational users. The algae can spread into thick mats with long stalks and has been described as resembling a sewage spill and having a woolly texture.

It attaches to rocks in the river bottom, smothering habitat for insects, and in turn, removing a food source for fish.

“Once you remove them (insects) young fish don’t have anything to eat,” said David Deen, a state representative, fishing guide and river steward for the Connecticut River Watershed Council. “Growth is slowed at best and at worst they could starve to death.”

The algae has preferred high-altitude, low nutrient rivers but now it’s showing up in other places, raising questions about whether it’s mutated and what triggers it’s growth.

New Zealand, Poland, Canada and northwestern states have been battling didymo and now Arkansas and Tennessee have large populations.

Underhill fly fishing guide Lawton Weber, who first spotted the didymo on the Connecticut River in Bloomfield in June, said he knew it was spreading in the U.S. and that Vermont had the habitat for it.

“It took me two seconds to go, ‘that’s didymo,”‘ he said.

“It scares me because first of all it’s an aesthetic eyesore when it’s in full bloom mode and it’s impact on the trout population is going to be significant.”

The biggest concern is keeping it from spreading. But that’s the challenge, since a single cell, invisible on clothing or gear, could infest a waterway.

On a steamy July Sunday North Pomfret fishing guide Brad Yoder estimated 150 inner tubes glided down the White River. “You don’t necessarily have to see it on the clothing or whatever because it’s cellular,” he said of the algae.

Anglers and anyone else using the rivers are asked to remove all visible clumps from their gear, clothing, shoes and boats and to scrub boats and soak clothes, felt-soled waders and other items in hot water and soap for 30 minutes.

For now the algae is in its early stages, forming nubby brown growths on rocks. No one knows what it will do next.

“I think all of the Northeast is tuned in to see what the effects will be so they can start taking preventive measures,” Russ said.