Rock snot threatens Michigan’s aquatic ecosystems

Michigan rivers continue to face an ecological threat known as didymo (Didymosphenia geminata), colloquially called “rock snot.”

Didymo differs from normal algae because it is brown and, unlike green algae, thrives in clean, cold water. It often covers stream beds and rocks with dense mats, destroying the natural habitat.

By covering riverbeds, Didymo displaces important food sources for fish such as trout, including stoneflies and larvae. This disturbance threatens to disrupt entire aquatic food chains and impacts fish populations and recreational activities that depend on healthy aquatic ecosystems, such as fishing.

Photo courtesy of Michigan Department of Environment, Great Lakes, and Energy.

Unlike the toxic blue-green algae in Lake Erie, Didymo poses no threat to human health.

Since its first discovery in Michigan’s St. Mary’s River in 2015, Didymo has been found in several other rivers, including the Manistee River and the Boardman River. Most recently, Didymo cells were detected in the Au Sable River.

Michigan’s economy is heavily dependent on tourism and recreational activities such as trout fishing. If the Didymo virus continues to spread, these sectors could be affected.

Efforts to eradicate Didymo have so far been unsuccessful, so the focus is now on prevention. Joanne Foreman, the invasive species communications coordinator for the Ministry of Natural Resources, suggests disinfecting equipment that comes into contact with Didymo.

“…because they’re single cells, they’re hard to see, but you could accidentally carry them from one stream to another, especially if you’re fishing multiple streams in one day,” Foreman explains. “So we found that something as simple as Formula 409 sprayed on your gear and waders can actually kill those didymo cells to make sure you don’t carry them from one place to another.”

Foreman also recommends visiting the Michigan Department of Natural Resources website, where she finds detailed decontamination guidelines and more information on protecting waterways.

By implementing proactive measures such as cleaning equipment, communities can help contain the spread of Didymo and ensure the longevity of their valued Lake Michigan rivers.