It’s a sickly yellow-green, gooey and stretchy, gripping rocks tenaciously and killing fish. No, it’s not the Swamp Monster – it’s a disgusting single-celled algae called ‘rock snot’, and it’s taking over rivers and streams in New York.

Officially known as Didymosphenia geminata, this fast-spreading algae has long been a bane of fishermen, quickly crowding out fish even in pristine waters. Ironically, sport fishermen are part of the problem, inadvertently spreading the muck from one stream to another with the felt bottoms of their wading boots. In fact, Didymo can survive for an astounding 90 days on a felt sole when kept in a cool, damp place.

Its presence was first confirmed in New York two years ago, but it has now made its way to waterways that provide drinking water for much of the state’s population. Investigators have confirmed the spread of rock snot along 12 miles of the Esopus Creek, which The New York Times calls a ‘legendary’ fly fishing stream.

Though it’s considered native to North America, its evolution over the years into such an aggressively multiplying species has caused the Environmental Protection Agency to label it as invasive. There are no known ways to eradicate Didymo once it’s established, so the best line of offense, according to a New York state official, is to prevent its spread in the first place.

As it turns out, fishermen’s boots are a virtual superhighway for harmful species. In addition to Didymo, other invasive species that can be transported by fishermen include the whirling disease parasite. Fishermen are encouraged to submerge their waders in a solution of water and bleach to kill cells before they can spread.