By Erin Kelley

Lawton Weber was looking forward to a day on the Upper Connecticut River with a friend this June, but less than 100 feet from where they launched their boat the two men drifted over something disturbing; a big clot of rock snot.

Didymo, or Didymosphenia geminata, is an invasive freshwater algae that looks, acording to Weber, like “cardboard-colored toilet paper.” It clings to rocks and blooms in sunny, dry weather and calm, clear water. Weber noticed small to medium-size patches covering all rocks in the area.


According to the New Hampshire Department of Environmental Services, when Didymo reaches full bloom it can form a four-inch thick carpet that covers all rock surfaces in a riverbed. This can smother aquatic plants and destroy fish habitat. Worse, there are currently no known methods for controlling or eradicating didymo once it infests a water body.

Weber is familiar with the algae from visits to New Zealand, where it has infested lakes and rivers after being transported on clothing and water-absorbent gear.

“It’s alarming,” said Weber, a fishing guide. “Once it’s in the river, it’s in the river for good.”

The algae has infested the Connecticut and White Rivers, and concern is growing that it will damage other New England fisheries. Today the New York State Department of Environmental Conservation released the news that it has been found in the lower Batten Kill.

Click here to learn more about rock snot, including how to prevent its spread.