Dreaded Didymo - Or 'Rock Snot' - Found In Upper Manistee River

Press release from Michigan DNR:

Dec. 6, 2021

Contact: Bill Keiper, 517-342-4087 or Joanne Foreman, 517-284-5814 Agency: Natural Resources

Dec. 6, 2021

The Michigan departments of Environment, Great Lakes, and Energy and Natural Resources confirmed a report of didymo, a nuisance freshwater alga, in a stretch of the Upper Manistee River in Kalkaska County. Also known as rock snot despite its coarse, woolly texture, didymo can grow into thick mats that cover the river bottom.

Can't see the table below? Click here to view the original story.

"Didymo has potential to be a nasty nuisance species in Michigan's cold-water fisheries," said Samuel Day, a water quality biologist with the Little Traverse Bay Bands of Odawa Indians. "Unlike the harmful algal blooms that plague areas of the Great Lakes due to warm temperatures and excess nutrients, didymo blooms form in cold, low-nutrient streams that most folks would generally consider pristine and great habitat for trout. Didymo can become a problem when it blooms, covering streambeds and reducing habitat for macroinvertebrates, which are important food for fish."

Can't see the table below? Click here to view the original story.

The Manistee River detection suggests didymo's distribution in Michigan waters may be more widespread than previously expected. LSSU's ongoing efforts will help guide didymo research and management needs statewide.

Didymo, a microscopic diatom (single-celled alga), may be present but undetected in some waterways until changes in water quality cause it to "bloom" or develop long stalks, making it visible on hard surfaces in the streambed. Further understanding of changes that trigger blooms may also help combat the species' negative environmental impacts.

Currently, there are no effective methods to eradicate didymo once it is established in a river or stream. To prevent spreading didymo and other aquatic invasive species to new locations, it is critical for recreational users to thoroughly clean, drain and dry waders, equipment and boats upon leaving a waterway.

• Clean by removing mud and debris from all surfaces.
• Drain water from all bilges, wells and tanks.
• Dry equipment for at least five days or disinfect with hot water or a dilute bleach solution.

Can't see the table below? Click here to view the original story.

Find more information on didymo and how to identify it at Michigan.gov/Invasives.

Michigan's Invasive Species Program is cooperatively implemented by the Department of Environment, Great Lakes, and Energy, the Department of Natural Resources, and the Department of Agriculture and Rural Development.

/Note to editors: Accompanying photos are available below for download. Suggested captions and photo credit information follow:

Hook: Didymo from the Upper Manistee River caught on fishing gear. Photo courtesy of Samuel Day, LTBB.

Slide: A view of didymo cells and stalks through a microscope. Photo courtesy of Samuel Day, LTBB.

Manistee: Didymo growth on gravel in the Manistee River appears dark brown. Areas where thick growth sloughs off looks woolly and light tan, exposes clean substrate underneath. Photo courtesy of EGLE.

Strands: Didymo strands on substrate in the St. Marys River. Photo courtesy of EGLE.

Cell: A single didymo cell magnified. Photo courtesy of Julianne Heinlein, Great Lakes Environmental Center, Inc./

This press release was produced by the Michigan DNR. The views expressed here are the author’s own.