Didymo algal blooms in the Boardman River

The Michigan Department of Environment, Great Lakes, and Energy has confirmed the presence of didymo (Didymosphenia geminata), a troublesome algae also known as rock snot, in a section of the Boardman River in the township of Blair, Grand Traverse County.

Flowers of Didymo, a microscopic diatom (unicellular algae), were discovered on the Upper Manistee River in Kalkaska County in December 2021 and have been found in the St. Marys River in the Upper Peninsula since 2015.

Didymo stalks form coarse and fibrous mats resembling wet wool or cotton.

A photo of the suspected Didymo, posted to a Michigan Sportsman online forum on Aug. 17, was forwarded to EGLE and staff at the Department of Natural Resources the next day. EGLE Invasive Aquatic Species Program Coordinator Sarah LeSage visited Shumsky’s Canoe Launch and a bridge access on East River Road in Blair Township on August 22 to collect samples that were reviewed by the Great Lakes Environmental Center the next day.

Points on the Boardman River, including Shumsky’s launch, were surveyed in May as part of a Didymo survey of 12 rivers in northern Michigan following the Upper Manistee discovery. Didymo was not found on the Boardman or any other river at that time.

Not your typical algae

Unlike the harmful algal blooms that plague areas of the Great Lakes and some inland lakes due to warm temperatures and excess nutrients, didymo blooms form in cold, nutrient-poor streams that are generally considered pristine — the same streams prized for their sport fishing.

Didymo mats can cover riverbeds and reduce habitat for macroinvertebrates, including mayfly and caddisfly nymphs, which are important food for fish.

“We don’t have many historical samples to indicate whether Didymo is present but undiscovered in other Michigan waterways,” LeSage said. “It’s possible that environmental factors, such as changes in water chemistry or quality, cause it to ‘bloom’ or develop long stalks, making previously undetected algal cells now visible on hard surfaces in the river bed.”

What is being done

Since 2015, the Michigan Invasive Species Grant Program has supported researchers at Lake Superior State University’s Center for Freshwater Research and Education in a comprehensive study of the occurrence of Didymo in the St. Marys River and Upper Peninsula waters, the risk of spread, and why it annoying blooms are increasing – a phenomenon that can be observed worldwide.

For information on the ongoing efforts of Didymo and LSSU, see the June 9, 2022 NotMISpecies webinar, Didymo: What you need to know, presented by Dr. Ashley Morke.

During the year EGLE and DNR have increased their relationships with partners including outfitters and bait shops serving the Upper Manistee River. In turn, these partners have encouraged boaters, anglers and others to adopt practices that prevent the spread of didymo via boats, gear and waders.
New signs have been installed at access points along the Upper Manistee, reminding users to “Clean, Dump, Dry.” Similar public relations activities are being undertaken along the Boardman River.

Prevention is key

There are currently no effective methods to eradicate didymo once it has become established in a river or stream. To prevent the proliferation of didymo and other invasive aquatic species to new locations, it is vital for recreational users to thoroughly clean, drain and dry waders, gear and boats when exiting a waterway.

Clean by removing mud and dirt 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 diluted bleach solution.

Visit the Didymo page at Michigan.gov/Invasives for additional recommendations.

Identify and report Didymo

Despite its slimy nickname, Didymo has a coarse texture reminiscent of wet wool. It can appear as small, cotton ball-sized patches or thick blankets of rope-like threads that flow in currents.

If you observe Didymo in the water, make note of the location and report it via the Midwest Invasive Species Information Network, available online at MISIN.msu.edu or as a downloadable smartphone app. The MISIN smartphone app records a GPS fix point when reporting on site; You can also upload photos with a report.

For more information on Didymo and his identification, visit Michigan.gov/Invasives.

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

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