Those out in the Manistee River may continue to notice a brown gunk clinging to rocks or trees under the surface.
Didymo, most commonly referred to as rock snot is a kind of algae that continues to spread in the upper Manistee River. The appearance of rock snot was first reported last fall, but it still continues to be a problem. Although it is usually microscopic, strands can grow up to six inches thick. Rock snot is not harmful, but it makes swimming and boating difficult and traps sediment that feeds trout.
Didymo is native to northern regions of Europe, Asia and North America in places like Lake Superior and parts of Canada, according to Michigan’s Invasive Species Program. Although cells have been documented in the Great Lakes Basin and Michigan waters in low abundance, their nuisance blooms are a recent issue and first appeared in St. Marys River in 2015.
According to Michigan State ANR, researchers are still working to figure out what triggers didymo’s nuisance blooms. Scientists believe this could be because of changing environmental conditions, or it could be didymo spreading to new waterways on fishing gear, which is the common way nuisance species spread. Didymo can survive for 40 days in cool, dark, dam conditions such as on angling equipment, neoprene and felt-soled waders and boots, Michigan State ANR says.
“Right now, didymo is a big puzzle with a lot of people working to address it. We need to find out why it’s showing up where it is and more importantly, how best to decontaminate gear to prevent it from spreading,” said Ann Miller, an aquatic biologist and avid Manistee River fly fisher. “Right now, many local fishing guides are doing their best to avoid the stretch of the Manistee where didymo is blooming but fishing is their livelihood.”
Three things can be done to prevent the spread:
- Cleaning up mud, debris and plant material from boats
- Draining wells and bait buckets
- Decontaminating and drying gear for at least five days before going to another body of water
Other things to keep in mind if you are fishing in water with a known rock snot population is to plan time to decontaminate between trips, avoid going to multiple rives in a single day and designating specific gear to use only in infested water.
For more information on preventing the spread of aquatic invasive species on boating and fishing equipment, .
To report a sighing of the rock snot, . You will have to make an account before you can report your observation though.
You can also report rock snot by emailing the location and photos to EGLE-WRD-AIP@Michigan.gov.
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