What is pond scum?

It's one of those things where you can't really define it, but “I know it when I see it.”

When a university's credit union is sold off to a corporation, and this corporation later sends a commercial solicitation which is designed to imitate the university's employee benefits mailings (though the credit union no longer has any connection to the university), well, I feel pretty sure that's pond scum.

I guess I'm looking for another bank here soon.