OSCODA COUNTY- Didymo cells have been found in algae samples taken from submerged rocks and debris at two boating access sites on the Au Sable River north of Luzerne in Oscoda County, Michigan.
Sampling conducted by Michigan Trout Unlimited in late April found several didymo cells at the Parmalee Canoe Launch off North Red Oak Road and one cell just downstream at the Whirlpool access off West Cherry Creek Road. No evidence of didymo was found in samples taken upstream at the McMasters Bridge Road access, further downstream or in a number of tributaries sampled to date.
Didymo, also known as “rock snot,” is a microscopic diatom (single-celled alga) that thrives in cold, low-nutrient streams generally considered pristine. Under the right conditions, cells can form extensive stalks, or blooms, creating dense mats that cover the stream bed and reduce habitat for macroinvertebrates including mayfly, caddisfly and stonefly nymphs, which are crucial food sources for fish.
Though no blooms have been observed at either of the two Au Sable River access sites, Michigan Trout Unlimited is joining the Michigan departments of Natural Resources and Environment, Great Lakes, and Energy to urge anglers and all stream users to properly clean waders, boats and equipment between every site visit.
Didymo is believed to be native to at least parts of the Great Lakes basin; however, its exact native range is unknown. Blooms are recent phenomena first observed in Michigan waters in 2015 in the St. Marys River and then in the Manistee and Boardman rivers in 2021 and 2022, respectively. Scientists are still researching the causes of blooms.
Didymo blooms appear to be sporadic and do not persist throughout the entire year or every fishing season. This provides some relief, but vigilance and decontamination efforts remain important to reduce harmful effects on streams.
Though there is no known treatment for didymo, efforts to understand its extent and behavior in Michigan waters are ongoing.
To prevent didymo and other damaging species from hitchhiking on your waders, watercraft and gear, pack a scrub brush, towels and a chemical disinfectant for use when you exit the water.
Always clean, drain and dry your waders, boots, boats and other gear between trips or before moving to a new body of water. Using different gear for each stream can reduce the potential for spread.
Take extra precaution in areas with known or suspected didymo or invasive species. In addition to removing debris and mud, the State of Michigan recommends using a chemical disinfectant to achieve maximum decontamination for didymo and invasives like New Zealand mudsnail.
Disinfectants with documented effectiveness for these species include:
- Products such as Formula 409 Antibacterial All-Purpose Cleaner: Apply to waders and gear and allow to soak for at least five minutes.
- Bleach: Apply a solution equivalent to 1 ounce of bleach per 1 gallon of water (at least a 2% bleach solution) and let stand for 20 minutes.
- Virkon Aquatic: Apply a solution of 20 grams per liter of water and let stand for 20 minutes (see manufacturer’s label for additional guidance).
- Any chemical disinfectants should be applied to waders and gear on land, at a reasonable distance from the water, to avoid accidentally getting the disinfectants into surface waters.
Public reporting plays an important role in early detection of invasive and nuisance species. Anyone encountering suspected didymo in new locations is asked to photograph and report the find.
To report didymo, use the Eyes in the Field online reporting system. Be sure to include up to three photos to aid in verification.
For more information on decontamination or aquatic invasive species, visit Michigan.gov/Invasives.
