Learn More About Rock Snot

What is Rock Snot?

Didymosphenia geminata, aka “rock snot” or “didymo” is an invasive stalk-producing alga found in the St. Marys River in Michigan. This is currently the only location that rock snot is found in Michigan.

Aside from being visually unappealing, it poses a threat to the ecosystem due to its long stalks that can smother the bottom of the river, potentially affecting the organisms that live there. Additionally, the dead stalks that drift along the surface often get caught on fishing line or boat motors.

Didymo blooms in cold, low-nutrient, and fast flowing waters and was found in the St. Marys in 2014. Outside of Michigan, it can be found in multiple locations including the Pacific Northwest and even New Zealand!

All of the brown stalks you see pictured are strands of rock snot. While it may look slimy, it actually has a texture similar to wet wool.

Current and Future Projects

A LSSU senior thesis project took place focusing on rock snot removal and the impacts it has on benthic macroinvertebrates, like crayfish and aquatic insects. This study was conducted in the Little Rapids of the St. Marys River in the summer of 2020.

Future research includes assessing rock snot’s impacts on salmonid spawning and habitat use.

What Can You Do to Stop the Spread?

  • Always clean your boats, waders, and other gear after entering the St. Marys and before entering a new body of water.
  • Learn more about this invasive and spread the word!

Brady Hess (Fisheries and Wildlife Management, left) and Molly Wozniak (Fisheries and Wildlife Management, right) are hard at work conducting research about the removal of rock snot and its impacts on benthic organisms.

Special thanks to Michigan Sea Grant’s Environmental Internship for providing the opportunity to create this page.