Researchers still don't know much about didymo or "rock snot," a microscopic algae that can bloom into thick, slimy mats on rivers.
But statewide monitoring has recently revealed the algae cells in the Au Sable River. The state is now calling on boaters and anglers to take precautions to reduce the spread of didymo.
Billy Keiper, an aquatic biologist with the Michigan Department of Environment, Great Lakes, and Energy, said the state isn't entirely sure what the long-term impacts of didymo are on aquatic ecosystems.
"Anytime you blanket a stream bed with something, you're going to have food web shifts," Keiper said. "Macroinvertebrates like insects, that fish feed on, could get crowded out. We just don't know exactly what to expect from the scale."
Kepier said it's a debate whether didymo is invasive in Michigan — the algae dates back centuries — but didymo blooms are a new phenomena and only appeared in Michigan within the last decade.
Understanding what's spurring blooms is a hot research topic, according to Keiper. Past blooms have occurred in cold, low-nutrient rivers like the Manistee and Boardman, and blooms are potentially linked to environmental changes.
"We're not sure whether it's a different strain of didymo we don't now about yet, or if it's linked to changes in water quality or shade or temperature," Keiper said. "It's got a lot of scientists scratching their heads right now."
While the science catches up, Keiper said the state is treating didymo like an invasive species. If allowed to go unchecked, he said there are concerns blooms could threaten trout fisheries like those on the "blue-ribbon" Au Sable.
"[During past blooms] a lot of the angling community was pretty concerned, and they saw some short-term changes (with) fish moving out of those areas," Keiper said. "... Right now, we're just trying to get folks aware, make sure they know it's in the system and keep their gear clean."
Boaters and anglers on the Au Sable are advised to "clean, drain and dry" their gear and boats before switching to new waterbodies to prevent the didymo from spreading.
For more information about how to reduce the spread of didymo and aquatic invasives like the New Zealand mudsnails, check out Trout Unlimited's decontamination guide.
