Identification of algae requires looking at it under a microscope.  This looks part of a large algae mat that was probably on the bottom of the lake and died.  Decomposition leads to the release of CO2 and other gasses that cause pieces of the algae mat to float and wash ashore.  This summer's heat in combination with above average rainfall and high water levels has led to more algae growth than usual in many lakes around Michigan.

 In short, it is probably nothing to worry about but identification to species is not possible with these photos - and since these algae cells are likely dead and decomposing it may not be possible to ID them even with a microscope.