GRAND TRAVERSE COUNTY, Mich. – Didymo, a nuisance alga known as “rock snot” has been identified in a stretch of the Boardman River in Blair Township in Grand Traverse County.
This alga can make recreation unpleasant and is present in some Michigan waters. Blooms of didymo were found in 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.
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The investigation began when a photo of suspected didymo was posted on Aug. 17 to a Michigan Sportsman online forum and forwarded to EGLE and the Department of Natural Resources staff the next day.
On Aug. 22, samples were taken and the next day the samples were verified by the Great Lakes Environmental Center.
Let’s talk about Michigan’s invasive aquatic plants: How to identify them and the dangers they pose
How to identify rock snot
- Didymo is a microscopic alga (diatom) that produces stalks that form thick mats on hard surfaces like rocks in stream beds.
- Looks and feels like white or brown wet wool.
- Ranges from small, cotton ball-sized patches to thick blankets and long, rope-like strings that flow in currents.
- Although often referred to as “rock snot,” didymo is not slimy.
Where is it found?
It thrives in low-nutrient cold water rivers and streams. Didymo cells have been documented in the Great Lakes Basin and Michigan waters in low abundance. Nuisance blooms have been documented in Michigan in the Upper Manistee and St. Marys rivers.
Didymo mats can cover streambeds and reduce habitat for macroinvertebrates including mayfly and caddisfly nymphs, which are important food for fish.
“We don’t have a lot of historical samples to indicate whether didymo may be present but undetected in other Michigan waterways,” said LeSage. “It’s possible that environmental factors like changes in water chemistry or quality are causing it to ‘bloom’ or develop long stalks, making previously undetected alga cells now visible on hard surfaces in the streambed.”
Why is it a concern?
Didymo can be transported on boats, anchors and fishing gear such as waders, felt-soled boots and nets. It can create thick mats that can cover river and stream bottoms. It alter habitat and food resources for fish and make recreation unpleasant.
What’s being done?
There are no effective ways to eradicate didymo once it’s established in a river or stream.
To prevent the spread of didymo, people should take the following steps:
- 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 diluted bleach solution.
If you find didymo, you should report it online at MISIN.MSU.edu or as a downloadable smartphone app. The MISIN smartphone app will take a GPS location point if a report is made at the site; it also will allow you to upload photos with a report.