Originally Posted by Quarter Acre
Here's a link to a Pond Scum Field guide that may help...

https://www.townofchapelhill.org/home/showdocument?id=28866

I think the above guide is a good point to jump from, but something like this may need to be put under a microscope to help truly identify.

Noel, thanks for posting that resource.

P.S. If I had written that guide, then I would definitely include the line "Pond Scum Expert" on my tombstone.