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Invasive species of algae found in Boardman River near Traverse City

Didymo algae
Br3nda / Flickr
Didymo algae

An invasive species that threatens rivers and streams has been spotted in the Boardman River, near Traverse City.

It’s called “didymo,” but it also has an unappetizing nickname: Rock snot.

Didymo is a microscopic algae that, when it blooms, can carpet the bottoms of rivers, covering the food source for the tiny little insects that fish like to eat. Didymo prefers cold, pristine rivers and streams, exactly the places people like to go fishing.

Joanne Foreman is with the state’s invasive species program. She says it’s important that anglers use extreme caution when moving from one body of water to another.

“They are popular spots to be wading and angling that people might unknowingly carry those from one stream to another, as they visit different locations," Foreman said. “So we’re really pushing for folks that are visiting to take extra precautions to clean, drain and dry your gear".

The state’s confirmation of didymo in the Boardman River, in Blair Township, is the latest discovery of the harmful algae. It’s already been found in the Manistee and St. Mary’s rivers.

Right now there are no good ways to get rid of didymo (DID-uh-moh), so officials are focused on preventing its spread. Officials are asking people who spot didymo to report it to the state. You can learn how to do that at "".

Ed Ronco joined IPR as its news director in the summer of 2022, after eight years with KNKX Public Radio in Seattle/Tacoma, where he was the local host of All Things Considered.