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'Rock Snot' threatens Michigan's aquatic ecosystems

Didymo mat covering rocks in Michigan river.
Didymo mat covering rocks in Michigan river.

Michigan rivers continue to face an ecological threat known as didymo (Didymosphenia geminata), commonly referred to as "rock snot."

Didymo differs from typical algae because it is brown and, unlike green algae, thrives in clean, cold water. It often blankets stream beds and rocks with dense mats, disrupting natural habitats.

By covering streambeds, didymo displaces crucial food sources for fish such as trout, including stoneflies and larvae. This disturbance threatens to disrupt entire aquatic food chains, impacting fish populations and recreational activities dependent on healthy water ecosystems, such as fishing.

Didymo covers vegetation in an area of the Boardman River.
Photo courtesy of Michigan Department of Environment, Great Lakes, and Energy.
Didymo covers vegetation in an area of the Boardman River.

Unlike blue-green algae in Lake Erie, which is toxic, didymo poses no threat to human health.

Since its initial discovery in Michigan's St. Mary's River in 2015, didymo has been found in several other rivers, including the Manistee and Boardman Rivers. Most recently, didymo cells have been detected in the Au Sable River.

Michigan's economy heavily relies on tourism and recreational activities such as trout fishing, which could suffer if didymo continues to spread.

Efforts to eradicate didymo have been unsuccessful, prompting a focus on prevention. Joanne Foreman, the Invasive Species Communications Coordinator with the Department of Natural Resources, suggests disinfecting gear that comes into contact with didymo.

"...because you're talking about single cells, it's pretty hard to see them, but you could accidentally be carrying them from one stream to another, especially if you visit multiple streams in a day to go fishing," Foreman explains. "So we found that something as simple as Formula 409 sprayed on your gear, and on your waders, can actually kill those didymo cells to ensure you're not transporting them from one place to another."

Foreman also encourages individuals to visit Michigan's Department of Natural Resources website for detailed decontamination guidelines and further information on protecting waterways.

By implementing proactive measures such as equipment cleaning, communities can contribute to mitigating the spread of didymo and ensuring the longevity of their cherished Michigan rivers.

Zena is a senior at the University of Michigan with aspirations of becoming a broadcast journalist. She is interning in the Michigan Public newsroom.
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