A nuisance freshwater alga that messes with Michigan’s cold-water fisheries has been detected in a stretch of the Upper Manistee River in Kalkaska County for the first time in the Lower Peninsula, the Michigan Department of Natural Resources announced Monday, Dec. 6.
This highly invasive species of freshwater algae is called didymo or "rock snot" despite its coarse, woolly texture.
Didymo is problematic when it grows into thick mats that cover the river bottom reducing the habitat for the tiny organisms that small fish feed on. Those small fish in turn provide food for Michigan's prized sports fish, such as trout, the Detroit Free Press reports.
It has plagued the river and stream bottoms in the Upper Peninsula since 2015 when extensive mats of didymo were found on the Michigan side of the St. Marys River near Sault Ste. Marie, according to a press release issued by the Michigan DNR.
Pictured are didymo strands on substrate in the St. Marys River.
Photo provided/EGLEThere are no effective ways to eradicate didymo once it establishes in a river or stream.
"Didymo has potential to be a nasty nuisance species in Michigan’s cold-water fisheries," Samuel Day, a water quality biologist with the Little Traverse Bay Bands of Odawa Indians, said in the release. "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 on Nov. 14.
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 provided/EGLEThe Manistee River detection suggests didymo’s distribution in Michigan waters may be more widespread than previously expected, according to the release.
"Didymo can attach to fishing equipment, wading gear and other hard surfaces and be moved to new waterways," Bill Keiper, an aquatic biologist with EGLE’s Water Resources Division, said in the release. "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."
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, according to the Michigan DNR.
- 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.
If you observe didymo in the water, either as small, cotton ball-sized patches or thick blankets with rope-like strings that flow in currents, take photos, note the location and report it by using the Midwest Invasive Species Information Network, available online at MISIN.MSU.edu or as a downloadable smartphone app.
"Over the next few months, we’ll work with partners to assure aquatic invasive species signs are posted at access sites and to spread the Clean, Drain, Dry message to the fishing community," Keiper said in the release. "We want to encourage local fly shops, fishing guides and conservation groups to help out by stressing the importance of decontaminating gear and equipment to protect these waters from didymo and other aquatic invasive species."
Find more information on didymo and how to identify it at Michigan.gov/Invasives.
