ELIZABETHTOWN -- Didymo, an invasive species also known as rock snot,' has been found in the Mad River, a waterway that runs through the heart of Vermont.

A freshwater diatom, or microscopic alga, didymo erupts in noxious "blooms" covering rocky river beds with brown, clumpy growths that feel like wet wool, according to the Vermont Agency of Natural Resources. It is described as looking similar to a sewage spill with wet toilet paper streaming in the waterway.

According to a press statement, Vermont water-quality scientists confirmed the presence of didymo in the Mad River, the first time the invasive freshwater alga has been found within the Lake Champlain Basin.

Vermont scientist Dr. Leslie Matthews said a citizen spotted the didymo and provided a sample for testing.

Matthews said her investigation found didymo has spread in the Mad River in an area between Riverwatch Lane and just upstream of the bridge leading into Warren Village.

"Didymo is extensively coating the rocks with 75 to 100 percent coverage and up to 1 to 2 centimeters in thickness," Matthews said. "I have not yet investigated other sections of the river but would expect that additional areas of bloom are likely present in the river."

River conservationists are very concerned about the potential for spreading rock snot.

"The discovery of didymo in the Mad River is great cause for concern," said Caitrin Noel, watershed coordinator for Friends of the Mad River. "We are working hard to learn all we can about the extent of this, how to address it and will continue to study this in the future."

In a phone interview Friday, Noel said the Friends of Mad River board of directors just had a meeting and discussed the didymo.

"We're not sure yet how far it goes," she said. "We haven't had time to map the watershed. The general feeling is we're concerned about it, but we want to stay optimistic."

The organization has done a lot of outreach about didymo, she said.

"But the White River is so close to here, if you think about it, it's inevitable."

Didymo has specific habitat requirements, and needs shallow, fast-moving water with a rocky bottom to survive.

"It's not going to be able to live in every place in the Mad River," Noel said.

It dies back in the winter, but returns in the spring.