(WWJ) – An invasive, nuisance freshwater alga known as didymo, or “rock snot,” has been found in Michigan.
The Michigan departments of Environment, Great Lakes and Energy and Natural Resources say didymo was found 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, the DNR says.
This marks the first detection of didymo blooms in the Lower Peninsula, though back in 2015, extensive rock snot mats were found on the Michigan side of the St. Mary’s River near Sault Ste. Marie in the Upper Peninsula.
Officials say anglers who have encountered didymo-infested streams in the western or eastern U.S. know that rock snot is more than just a nuisance.
“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.”
Bill Keiper, an aquatic biologist with EGLE’s Water Resources Division, says “with each new detection, it becomes more important for people who fish, wade or boat to clean boats and equipment, including waders, after each use.”
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, the DNR says.
The DNR says didymo 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, the DNR says, 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.
More information on didymo and how to identify it can be found on the DNR's website.
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