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.
The Manistee River finding marks the first detection of didymo blooms in the Lower Peninsula. In 2015, extensive mats of didymo were found on the Michigan side of the St. Marys River near Sault Ste. Marie in the Upper Peninsula.
“Didymo can attach to fishing equipment, wading gear and other hard surfaces and be moved to new waterways,” said Bill Keiper, an aquatic biologist with EGLE’s Water Resources Division. “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.”
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.”
Day, who studied didymo in southeastern U.S. streams as a graduate student at Tennessee Technological University, discovered the algal blooms between the Three Mile Bend and Sharon Road Bridge landings on the Upper Manistee River while fishing with a friend Nov. 14. After
