Thank you for your question. I am sorry for the delay. It appears to be algae, a problem occuring in many waterways. Here is an article about it: http://www.miseagrant.umich.edu/explore/coastal-communities/harmful-algal-blooms-in-the-great-lakes/ You might like to contact your county Extension office directly for more assistance: https://www.canr.msu.edu/roscommon/index Good luck!

The algae appears to be a filamentous algae. Filamentous algae are a normal occurrence in lakes in Michigan and provide a valuable food source for a variety of lake organisms. If they grow to nuisance levels, that may be a sign of an over abundance of the nutrients nitrogen and phosphorus in the water. Here is a factsheet from Penn State on filamentous algae https://extension.psu.edu/filamentous-algae.